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Uyeda K. Short- and Long-Term Adaptation to Altered Levels of Glucose: Fifty Years of Scientific Adventure. Annu Rev Biochem 2021; 90:31-55. [PMID: 34153217 DOI: 10.1146/annurev-biochem-070820-125228] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
My graduate and postdoctoral training in metabolism and enzymology eventually led me to study the short- and long-term regulation of glucose and lipid metabolism. In the early phase of my career, my trainees and I identified, purified, and characterized a variety of phosphofructokinase enzymes from mammalian tissues. These studies led us to discover fructose 2,6-P2, the most potent activator of phosphofructokinase and glycolysis. The discovery of fructose 2,6-P2 led to the identification and characterization of the tissue-specific bifunctional enzyme 6-phosphofructo-2-kinase:fructose 2,6-bisphosphatase. We discovered a glucose signaling mechanism by which the liver maintains glucose homeostasis by regulating the activities of this bifunctional enzyme. With a rise in glucose, a signaling metabolite, xylulose 5-phosphate, triggers rapid activation of a specific protein phosphatase (PP2ABδC), which dephosphorylates the bifunctional enzyme, thereby increasing fructose 2,6-P2 levels and upregulating glycolysis. These endeavors paved the way for us to initiate the later phase of my career in which we discovered a new transcription factor termed the carbohydrate response element binding protein (ChREBP). Now ChREBP is recognized as the masterregulator controlling conversion of excess carbohydrates to storage of fat in the liver. ChREBP functions as a central metabolic coordinator that responds to nutrients independently of insulin. The ChREBP transcription factor facilitates metabolic adaptation to excess glucose, leading to obesity and its associated diseases.
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Affiliation(s)
- Kosaku Uyeda
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA;
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Kunz HH, Zamani-Nour S, Häusler RE, Ludewig K, Schroeder JI, Malinova I, Fettke J, Flügge UI, Gierth M. Loss of cytosolic phosphoglucose isomerase affects carbohydrate metabolism in leaves and is essential for fertility of Arabidopsis. PLANT PHYSIOLOGY 2014; 166:753-65. [PMID: 25104722 PMCID: PMC4213106 DOI: 10.1104/pp.114.241091] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2014] [Accepted: 08/04/2014] [Indexed: 05/18/2023]
Abstract
Carbohydrate metabolism in plants is tightly linked to photosynthesis and is essential for energy and carbon skeleton supply of the entire organism. Thus, the hexose phosphate pools of the cytosol and the chloroplast represent important metabolic resources that are maintained through action of phosphoglucose isomerase (PGI) and phosphoglucose mutase interconverting glucose 6-phosphate, fructose 6-phosphate, and glucose 1-phosphate. Here, we investigated the impact of disrupted cytosolic PGI (cPGI) function on plant viability and metabolism. Overexpressing an artificial microRNA targeted against cPGI (amiR-cpgi) resulted in adult plants with vegetative tissue essentially free of cPGI activity. These plants displayed diminished growth compared with the wild type and accumulated excess starch in chloroplasts but maintained low sucrose content in leaves at the end of the night. Moreover, amiR-cpgi plants exhibited increased nonphotochemical chlorophyll a quenching during photosynthesis. In contrast to amiR-cpgi plants, viable transfer DNA insertion mutants disrupted in cPGI function could only be identified as heterozygous individuals. However, homozygous transfer DNA insertion mutants could be isolated among plants ectopically expressing cPGI. Intriguingly, these plants were only fertile when expression was driven by the ubiquitin10 promoter but sterile when the seed-specific unknown seed protein promoter or the Cauliflower mosaic virus 35S promoter were employed. These data show that metabolism is apparently able to compensate for missing cPGI activity in adult amiR-cpgi plants and indicate an essential function for cPGI in plant reproduction. Moreover, our data suggest a feedback regulation in amiR-cpgi plants that fine-tunes cytosolic sucrose metabolism with plastidic starch turnover.
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Affiliation(s)
- Hans-Henning Kunz
- Department of Botany II, University of Cologne, 50674 Cologne, Germany (H.-H.K., S.Z.-N., R.E.H., K.L., U.-I.F., M.G.);Division of Biological Sciences, Cell and Developmental Biology Section, University of California, San Diego, La Jolla, California 92093 (J.I.S.); andInstitute of Biochemistry and Biology, University of Potsdam, 14476 Golm, Germany (I.M., J.F.)
| | - Shirin Zamani-Nour
- Department of Botany II, University of Cologne, 50674 Cologne, Germany (H.-H.K., S.Z.-N., R.E.H., K.L., U.-I.F., M.G.);Division of Biological Sciences, Cell and Developmental Biology Section, University of California, San Diego, La Jolla, California 92093 (J.I.S.); andInstitute of Biochemistry and Biology, University of Potsdam, 14476 Golm, Germany (I.M., J.F.)
| | - Rainer E Häusler
- Department of Botany II, University of Cologne, 50674 Cologne, Germany (H.-H.K., S.Z.-N., R.E.H., K.L., U.-I.F., M.G.);Division of Biological Sciences, Cell and Developmental Biology Section, University of California, San Diego, La Jolla, California 92093 (J.I.S.); andInstitute of Biochemistry and Biology, University of Potsdam, 14476 Golm, Germany (I.M., J.F.)
| | - Katja Ludewig
- Department of Botany II, University of Cologne, 50674 Cologne, Germany (H.-H.K., S.Z.-N., R.E.H., K.L., U.-I.F., M.G.);Division of Biological Sciences, Cell and Developmental Biology Section, University of California, San Diego, La Jolla, California 92093 (J.I.S.); andInstitute of Biochemistry and Biology, University of Potsdam, 14476 Golm, Germany (I.M., J.F.)
| | - Julian I Schroeder
- Department of Botany II, University of Cologne, 50674 Cologne, Germany (H.-H.K., S.Z.-N., R.E.H., K.L., U.-I.F., M.G.);Division of Biological Sciences, Cell and Developmental Biology Section, University of California, San Diego, La Jolla, California 92093 (J.I.S.); andInstitute of Biochemistry and Biology, University of Potsdam, 14476 Golm, Germany (I.M., J.F.)
| | - Irina Malinova
- Department of Botany II, University of Cologne, 50674 Cologne, Germany (H.-H.K., S.Z.-N., R.E.H., K.L., U.-I.F., M.G.);Division of Biological Sciences, Cell and Developmental Biology Section, University of California, San Diego, La Jolla, California 92093 (J.I.S.); andInstitute of Biochemistry and Biology, University of Potsdam, 14476 Golm, Germany (I.M., J.F.)
| | - Joerg Fettke
- Department of Botany II, University of Cologne, 50674 Cologne, Germany (H.-H.K., S.Z.-N., R.E.H., K.L., U.-I.F., M.G.);Division of Biological Sciences, Cell and Developmental Biology Section, University of California, San Diego, La Jolla, California 92093 (J.I.S.); andInstitute of Biochemistry and Biology, University of Potsdam, 14476 Golm, Germany (I.M., J.F.)
| | - Ulf-Ingo Flügge
- Department of Botany II, University of Cologne, 50674 Cologne, Germany (H.-H.K., S.Z.-N., R.E.H., K.L., U.-I.F., M.G.);Division of Biological Sciences, Cell and Developmental Biology Section, University of California, San Diego, La Jolla, California 92093 (J.I.S.); andInstitute of Biochemistry and Biology, University of Potsdam, 14476 Golm, Germany (I.M., J.F.)
| | - Markus Gierth
- Department of Botany II, University of Cologne, 50674 Cologne, Germany (H.-H.K., S.Z.-N., R.E.H., K.L., U.-I.F., M.G.);Division of Biological Sciences, Cell and Developmental Biology Section, University of California, San Diego, La Jolla, California 92093 (J.I.S.); andInstitute of Biochemistry and Biology, University of Potsdam, 14476 Golm, Germany (I.M., J.F.)
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Wang C, Wang CY, Zhao XQ, Chen RF, Lan P, Shen RF. Proteomic analysis of a high aluminum tolerant yeast Rhodotorula taiwanensis RS1 in response to aluminum stress. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2013; 1834:1969-75. [DOI: 10.1016/j.bbapap.2013.06.014] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/07/2013] [Revised: 06/17/2013] [Accepted: 06/20/2013] [Indexed: 11/25/2022]
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Wu MX, Smyth DA, Black CC. Regulation of pea seed pyrophosphate-dependent phosphofructokinase: Evidence for interconversion of two molecular forms as a glycolytic regulatory mechanism. Proc Natl Acad Sci U S A 2010; 81:5051-5. [PMID: 16593500 PMCID: PMC391635 DOI: 10.1073/pnas.81.16.5051] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Two molecular forms of pyrophosphate-dependent phosphofructokinase (PP(i)-PFK; pyrophosphate:D-fructose-6-phosphate 1-phosphotransferase; EC 2.7.1.90) have been found whose activity depends upon association and dissociation characteristics regulated by fructose 2,6-bisphosphate (Fru-2,6-P(2)). PP(i)-PFK was purified 200-fold from cotyledons of germinating pea seeds and found to exist in two interconvertible molecular forms. The two forms of PP(i)-PFK have sedimentation coefficients of 6.3 and 12.7 S during ultracentrifugation in sucrose density gradients and also differ both in sensitivity to the activator Fru-2,6-P(2) and in affinity for the substrate fructose 6-phosphate. The major component of enzyme activity is in the large form (12.7 S), but the small, less-active, form (6.3 S) predominates when the enzyme preparation is extracted and stored in buffer without Fru-2,6-P(2) and glycerol. Urea (1 M) or pyrophosphate (20 mM) treatment results in at least a 50% loss of activity in the glycolytic direction, whereas these treatments had much less influence on the gluconeogenic direction activity. Concomitant with the loss of glycolytic activity the enzyme dissociates into the small form. Fru-2,6-P(2) stabilizes the large form of the enzyme against the dissociating effects of pyrophosphate and prevents the inactivation in the glycolytic direction during either urea or pyrophosphate treatment. The small molecular form of the enzyme is converted into the large form in the presence of Fru-2,6-P(2). We propose that glycolytic and gluconeogenic hexose metabolism in plants includes a regulatory mechanism induced by Fru-2,6-P(2) that involves the interconversion of two molecular forms of PP(i)-PFK.
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Affiliation(s)
- M X Wu
- Biochemistry Department, University of Georgia, Athens, GA 30602
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Gibson DM, Shine WE. Uridine diphosphate glucose breakdown is mediated by a unique enzyme activated by fructose 2,6-bisphosphate in Solanum tuberosum. Proc Natl Acad Sci U S A 2010; 80:2491-4. [PMID: 16593304 PMCID: PMC393851 DOI: 10.1073/pnas.80.9.2491] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In the presence of inorganic phosphate, uridine 5'-diphosphate glucose (UDPG) is specifically hydrolyzed to glucose 1-phosphate and UDP by a unique enzyme, UDPG phosphorylase. The activity of the enzyme was maximally stimulated by fructose 2,6-bisphosphate, a regulatory metabolite recently discovered in both plants and animals, and by 2-phosphoglyceric acid. At 1 muM, fructose 2,6-bisphosphate stimulated UDPG phosphorolysis 10-fold, whereas 2-phosphoglyceric acid was required at higher concentrations (100 muM) to produce a similar effect. Fructose 2,6-bisphosphate appears to increase the affinity of the enzyme for inorganic phosphate, with a change in K(m) from 1.6 mM to 0.3 mM. The results suggest that fructose 2,6-bisphosphate participates in the regulation of other pathways of carbohydrate metabolism in addition to playing its recognized role in glycolysis and gluconeogenesis.
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Affiliation(s)
- D M Gibson
- Frito-Lay Research, 900 N, Loop 12, Irving, Texas 75061
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Lim H, Cho MH, Jeon JS, Bhoo SH, Kwon YK, Hahn TR. Altered expression of pyrophosphate: fructose-6-phosphate 1-phosphotransferase affects the growth of transgenic Arabidopsis plants. Mol Cells 2009; 27:641-9. [PMID: 19533038 DOI: 10.1007/s10059-009-0085-0] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2008] [Revised: 04/15/2009] [Accepted: 04/20/2009] [Indexed: 11/30/2022] Open
Abstract
Pyrophosphate: fructose-6-phosphate 1-phosphotransferase (PFP) catalyzes the reversible interconversion of fructose-6-phosphate and fructose-1,6-bisphosphate, a key step in the regulation of the metabolic flux toward glycolysis or gluconeogenesis. To examine the role of PFP in plant growth, we have generated transgenic Arabidopsis plants that either overexpress or repress Arabidopsis PFP sub-unit genes. The overexpressing lines displayed increased PFP activity and slightly faster growth relative to wild type plants, although their photosynthetic activities and the levels of metabolites appeared not to have significantly changed. In contrast, the RNAi lines showed significantly retarded growth in parallel with the reduced PFP activity. Analysis of photosynthetic activity revealed that the growth retardation phenotype of the RNAi lines was accompanied by the reduced rates of CO(2) assimilation. Microarray analysis of our transgenic plants further revealed that the altered expression of AtPFPbeta affects the expression of several genes involved in diverse physiological processes. Our current data thus suggest that PFP is important in carbohydrate metabolism and other cellular processes.
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Affiliation(s)
- Hyemin Lim
- Plant Metabolism Research Center and Graduate School of Biotechnology, Kyung Hee University, Yongin 446-701, Korea
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Winkler C, Delvos B, Martin W, Henze K. Purification, microsequencing and cloning of spinach ATP-dependent phosphofructokinase link sequence and function for the plant enzyme. FEBS J 2006; 274:429-38. [PMID: 17229148 DOI: 10.1111/j.1742-4658.2006.05590.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Despite its importance in plant metabolism, no sequences of higher plant ATP-dependent phosphofructokinase (EC 2.7.1.11) are annotated in the databases. We have purified the enzyme from spinach leaves 309-fold to electrophoretic homogeneity. The purified enzyme was a homotetramer of approximately 52 kDa subunits with a specific activity of 600 mU x mg(-1) and a Km value for ATP of 81 microm. The purified enzyme was not activated by phosphate, but slightly inhibited instead, suggesting that it was the chloroplast isoform. The inclusion of adenosine 5'-(beta,gamma-imido)triphosphate was conducive to enzyme activity during the purification protocol. The sequences of eight tryptic peptides from the final protein preparation, which did not utilize pyrophosphate as a phosphoryl donor, were determined and an exactly corresponding cDNA was cloned. The sequence of enzymatically active spinach ATP-dependent phosphofructokinase suggests that a large family of genomics-derived higher plant sequences currently annotated in the databases as putative pyrophosphate-dependent phosphofructokinases according to sequence similarity is misannotated with respect to the cosubstrate.
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Van Schaftingen E. Fructose 2,6-bisphosphate. ADVANCES IN ENZYMOLOGY AND RELATED AREAS OF MOLECULAR BIOLOGY 2006; 59:315-95. [PMID: 3028056 DOI: 10.1002/9780470123058.ch7] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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Cséke C, Buchanan BB. An enzyme synthesizing fructose 2,6-bisphosphate occurs in leaves and is regulated by metabolite effectors. FEBS Lett 2001. [DOI: 10.1016/0014-5793(83)80226-9] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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Kruger NJ, Kombrink E, Beevers H. Pyrophosphate: fructose 6-phosphate phosphotransferase in germinating castor bean seedlings. FEBS Lett 2001. [DOI: 10.1016/0014-5793(83)80654-1] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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Balogh Á, Wong JH, Wötzel C, Soll J, Cséke C, Buchanan BB. Metabolite-mediated catalyst conversion of PFK and PFP: a mechanism of enyme regulation in green plants. FEBS Lett 2001. [DOI: 10.1016/0014-5793(84)80335-x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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A novel pyrophosphate fructose-6-phosphate 1-phosphotransferase from carrot roots Relation to PFK from the same source. FEBS Lett 2001. [DOI: 10.1016/0014-5793(88)80521-0] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Direct evidence that pyrophosphate: Fructose-6-phosphate phosphotransferase can act as a glycolytic enzyme in plants. FEBS Lett 2001. [DOI: 10.1016/0014-5793(89)81042-7] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Moriyama M, Nishisako M, Ueda J, Kannan Y, Ohta M, Sugano T. Changes in fructose-induced production of glucose in the rat liver following partial hepatectomy. Arch Biochem Biophys 1999; 371:53-62. [PMID: 10525289 DOI: 10.1006/abbi.1999.1422] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The fructose-induced production of glucose in the liver after partial hepatectomy (PH) was evaluated by using the liver-perfusion system. There was no significant difference in plasma glucose level between hepatectomized (HX) and sham-operated (SO) rats at 24 h after surgery, and, thereafter, almost similar levels were obtained in both groups. However, the level of serum free fatty acids (FFA) was significantly higher in HX rats than that in SO rats at 24 and 48 h after surgery. When both groups of rats were given fructose by gavage, the increment of plasma glucose was significantly larger in HX rats than in SO rats. Lactate infusion failed to increase the rate of glucose production in perfused livers of both HX and SO rats and there was no significant difference in the activity of hepatic phosphoenolpyruvate carboxykinase. By contrast, fructose infusion elicited a large increase in glucose production in the perfused livers of HX rats at 24 and 48 h after PH. The increase was closely associated with not the change in fructose 2,6-bisphosphate levels but the increment of the intracellular levels of citrate. Treatment of octanoate or oleate, which supplies acetyl-CoA via fatty acid oxidation, mimicked the fructose-induced increase in glucose production in SO rats with a concomitant increase in hepatic levels of citrate. These results suggest that the oxidation of FFA may play an important role in glucose production induced by fructose administration during the early phase of liver regeneration.
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Affiliation(s)
- M Moriyama
- College of Agriculture, Osaka Prefecture University, Sakai, Osaka, 599-8531, Japan.
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Abstract
Fructose-2,6-bisphosphate is an important intracellular biofactor in the control of carbohydrate metabolic fluxes in eukaryotes. It is generated from ATP and fructose-6-phosphate by 6-phosphofructo-2-kinase and degraded to fructose-6-phosphate and phosphate ion by fructose-2,6-bisphosphatase. In most organisms these enzymatic activities are contained in a single polypeptide. The reciprocal modulation of the kinase and bisphosphatase activities by post-translational modifications places the level of the biofactor under the control of extra-cellular signals. In general, these signals are generated in response to changing nutritional states, therefore, fructose-2,6-bisphosphate plays a role in the adaptation of organisms, and the tissues within them, to changes in environmental and metabolic states. Although the specific mechanism of fructose-2,6-bisphosphate action varies between species and between tissues, most involve the allosteric activation of 6-phosphofructo-1-kinase and inhibition of fructose-1,6-bisphosphatase. These highly conserved enzymes regulate the fructose-6-phosphate/fructose-1,6-bisphosphate cycle, and thereby, determine the carbon flux. It is by reciprocal modulation of these activities that fructose-2,6-bisphosphate plays a fundamental role in eukaryotic carbohydrate metabolism.
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Affiliation(s)
- D A Okar
- University of Minnesota, Medical School, Department of Biochemistry, Molecular Biology, and Biophysics, Minneapolis 55455, USA
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Botha AM, Botha FC. Induction of Pyrophosphate-Dependent Phosphofructokinase in Watermelon (Citrullus lanatus) Cotyledons Coincides with Insufficient Cytosolic D-Fructose-1,6-Bisphosphate 1-Phosphohydrolase to Sustain Gluconeogenesis. PLANT PHYSIOLOGY 1993; 101:1385-1390. [PMID: 12231792 PMCID: PMC160664 DOI: 10.1104/pp.101.4.1385] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
During germination of Citrullus lanatus, pyrophosphate-dependent phosphofructokinase (PFP) activity is induced. The peak of PFP activity coincides with the maximum gluconeogenic flux and high fructose-2,6-bisphosphate (Fru-2,6-P2) concentrations. Determination of cytosolic fructose-1,6 bisphosphatase (FBPase) activity in crude extracts is unreliable because of the high PFP activity. The FBPase activity, after correction for the contaminating PFP, is only one-third of the PFP activity. Purified cytosolic FBPase is inhibited by Fru-2,6-P2. The low cytosolic FBPase activity and high Fru-2,6-P2 most probably result in inadequate in vivo activity to catalyze the observed gluconeogenic flux. The total PFP activity is sufficient to catalyze the required carbon flux.
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Affiliation(s)
- A. M. Botha
- Department of Botany and Genetics, University of the Orange Free State, Bloemfontein 9300, South Africa
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CHO YONGKWEON. REACTION MECHANISM OF PYROPHOSPHATE-DEPENDENT PHOSPHOFRUCTOKINASE FROM PINEAPPLE LEAVES. J Food Biochem 1993. [DOI: 10.1111/j.1745-4514.1993.tb00862.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Champigny ML, Foyer C. Nitrate activation of cytosolic protein kinases diverts photosynthetic carbon from sucrose to amino Acid biosynthesis: basis for a new concept. PLANT PHYSIOLOGY 1992; 100:7-12. [PMID: 16653003 PMCID: PMC1075509 DOI: 10.1104/pp.100.1.7] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
The regulation of carbon partitioning between carbohydrates (principally sucrose) and amino acids has been only poorly characterized in higher plants. The hypothesis that the pathway of sucrose and amino acid biosynthesis compete for carbon skeletons and energy is widely accepted. In this review, we suggest a mechanism involving the regulation of cytosolic protein kinases whereby the flow of carbon is regulated at the level of partitioning between the pathways of carbohydrate and nitrogen metabolism via the covalent modulation of component enzymes. The addition of nitrate to wheat seedlings (Triticum aestivum) grown in the absence of exogenous nitrogen has a dramatic, if transient, impact on sucrose formation and on the activities of sucrose phosphate synthase (which is inactivated) and phosphoenolpyruvate carboxylase (which is activated). The activities of these two enzymes are modulated by protein phosphorylation in response to the addition of nitrate, but they respond in an inverse fashion. Sucrose phosphate synthase in inactivated and phosphoenolpyruvate carboxylase is activated. Nitrate functions as a signal metabolite activating the cytosolic protein kinase, thereby modulating the activities of at least two of the key enzymes in assimilate partitioning and redirecting the flow of carbon away from sucrose biosynthesis toward amino acid synthesis.
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Affiliation(s)
- M L Champigny
- Photosynthèse et Métabolisme (Unité de Recherche Associée Centre National de la Recherche Scientifique D 1128), Bâtiment 430, Université Paris-Sud, F-91405 Orsay cedex, France
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Hite DR, Bodson MJ, Outlaw WH. Enzymic potential for fructose 6-phosphate phosphorylation by guard cells and by palisade cells in leaves of the broad bean Vicia faba L. THE HISTOCHEMICAL JOURNAL 1992; 24:368-74. [PMID: 1321800 DOI: 10.1007/bf01046169] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Guard cells and palisade cells were dissected from freeze-dried leaflets of the broad bean, Vicia faba L. Individual cell samples (6-12 ng) were assayed for ATP-dependent and pyrophosphate-dependent phosphofructokinases. The assay indicator, NADH loss, was monitored in real time in oil droplets with a computer-driven microfluorometer. On a protein basis, both activities were 10-fold higher in guard cells than in palisade cells, indicating (i) elevated carbon metabolism in guard cells to meet demands for energy and carbon skeletons required during stomatal opening, and (ii) parallel glycolytic pathways in guard cells, one responsive to the potent regulatory metabolite fructose 2,6-bisphosphate and the other not. Future work will be devoted to clarifying the roles of the cytosolic and chloroplastic compartments in guard cells.
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Affiliation(s)
- D R Hite
- Department of Biological Science, Florida State University, Tallahassee 32306-3050
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Claassen PA, Budde MA, de Ruyter HJ, van Calker MH, van Es A. Potential Role of Pyrophosphate:Fructose 6-Phosphate Phosphotransferase in Carbohydrate Metabolism of Cold Stored Tubers of Solanum tuberosum cv Bintje. PLANT PHYSIOLOGY 1991; 95:1243-9. [PMID: 16668118 PMCID: PMC1077679 DOI: 10.1104/pp.95.4.1243] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
To gain a better understanding of the mechanism of cold induced sweetening, sugar accumulation in potato, Solanum tuberosum cv Bintje, was compared to the maximum activity of inorganic pyrophosphate (PPi):fructose 6-phosphate 1-phosphotransferase (EC 2.7.1.90) and the concentration of two regulatory metabolites. Mature tubers accumulated reducing sugars and sucrose at an almost linear rate of 13.4 and 5.2 micromole per day per gram dry weight at 2 degrees C and 4.5 and 1.3 micromole per day per gram dry weight, respectively, at 4 degrees C. During storage at 8 degrees C sugar accumulation was nil. Sugar accumulation was preceded by a lag phase of about 4 days. The accumulation of reducing sugars persisted for at least 4 weeks, whereas sucrose accumulation declined after 2 weeks of storage. The ratio of glucose:fructose changed concomitantly with sugar increase from 65:35 to equimolarity. The maximum activity of PPi:fructose 6-phosphate 1-phosphotransferase was 2.51 and 2.25 units per gram dry weight during storage at 2 and 8 degrees C, respectively. The temperature coefficient of this enzyme from potatoes kept at 2 or 8 degrees C was 2.12 and 2.48, respectively. The endogenous concentration of fructose 2,6-biphosphate increased from 0.15 to 1 nanomole per gram dry weight during storage at 2 and 4 degrees C but remained the same throughout storage at 8 degrees C. After exposure to 2 degrees C an initial increase in the concentration of PPi was observed from 4.0 to 5.6 nanomoles per gram dry weight. Pyrophosphate concentration did not change during storage at 4 degrees C but decreased slightly at 8 degrees C. All observed changes became annulled after transfer of cold stored tubers to 18 degrees C. These data strongly indicate that PPi:fructose 6-phosphate 1-phosphotransferase can be fully operational in cold stored potato tubers and the lack of increase in PPi concentration supports the functioning of this enzyme during sugar accumulation.
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Affiliation(s)
- P A Claassen
- ATO Agrotechnological Research Institute, Haagsteeg 6, 6700 AA Wageningen, The Netherlands
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Wong JH, Kiss F, Wu MX, Buchanan BB. Pyrophosphate Fructose-6-P 1-Phosphotransferase from Tomato Fruit : Evidence for Change during Ripening. PLANT PHYSIOLOGY 1990; 94:499-506. [PMID: 16667740 PMCID: PMC1077260 DOI: 10.1104/pp.94.2.499] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Three forms of pyrophosphate fructose-6-phosphate 1-phosphotransferase (PFP) were purified from both green and red tomato (Lycopersicon esculentum) fruit: (a) a classical form (designated Q(2)) containing alpha- (66 kilodalton) and beta- (60 kilodalton) subunits; (b) a form (Q(1)) containing a beta-doublet subunit; and (c) a form (Q(0)) that appeared to contain a beta-singlet subunit. Several lines of evidence suggested that the different forms occur under physiological conditions. Q(2) was purified to apparent electrophoretic homogeneity; Q(1) and Q(0) were highly purified, but not to homogeneity. The distribution of the PFP forms from red (versus green) tomato was: Q(2), 29% (90%); Q(1), 47% (6%); and Q(0), 24% (4%). The major difference distinguishing the red from the green tomato enzymes was the fructose-2,6-bisphosphate (Fru-2,6-P(2))-induced change in K(m) for fructose-6-phosphate (Fru-6-P), the ;green forms' showing markedly enhanced affinity on activation (K(m) decrease of 7-9-fold) and the ;red forms' showing either little change (Q(0), Q(1)) or a relatively small (2.5-fold) affinity increase (Q(2)). The results extend our earlier findings with carrot root to another tissue and indicate that forms of PFP showing low or no affinity increase for Fru 6-P on activation by Fru-2,6-P(2) (here Q(1) and Q(0)) are associated with sugar storage, whereas the classical form (Q(2)), which shows a pronounced affinity increase, is more important for starch storage.
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Affiliation(s)
- J H Wong
- Department of Plant Biology, Genetics and Plant Biology Building, University of California, Berkeley, California 94720
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24
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Cheng HF, Tao M. Differential proteolysis of the subunits of pyrophosphate-dependent 6-phosphofructo-1-phosphotransferase. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(19)39957-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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25
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26
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Hatzfeld WD, Stitt M. A study of the rate of recycling of triose phosphates in heterotrophic Chenopodium rubrum cells, potato tubers, and maize endosperm. PLANTA 1990; 180:198-204. [PMID: 24201945 DOI: 10.1007/bf00193996] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 07/17/1989] [Indexed: 06/02/2023]
Abstract
We have investigated whether starch accumulation in heterotrophic cell-suspension cultures of Chenopodium rubrum L., developing potato (Solarium tuberosum L.) tubers or maize (Zea mays L.) endosperm involves import of triose phosphates or of hexose units into the plastid, and whether there is a rapid recycling of triose phosphates back to hexose phosphates in the cytosol of these tissues, (i) Cell suspensions, potato tubers or intact maize kernels were supplied with [1-(14)C] glucose or [6-(14)C]glucose. The glucosyl residues from starch were isolated and degraded by an enzymic procedure to determine how much radioactivity had been redistributed into the opposite half of the glucose molecule. Randomisation was incomplete, affecting only 18%-38% of the molecules in Chenopodium, 16%-26% of the molecules in potato, or 30% of the molecules in maize. It is concluded that the major route for starch synthesis involves import of hexose units, (ii) The glucosyl and fructosyl moieties of sucrose were isolated and degraded to determine the extent of recycling in the cytosol. There was significant randomisation, lying between 30%-40% in Chenopodium, 20%-26% in potato, and 8%-12% in maize. It is concluded that there is considerable recycling of triose phosphates in the cytosol. (iii). Sucrose from cells supplied with [1-(14)C]glucose was more randomised than sucrose from cells supplied with [6-(14)C]glucose. This is explained in terms of the oxidative pentose-phosphate pathway (iv). Equations are used to estimate the rate of recycling from triose phosphates to hexose phosphates in the cytosol. The estimated rate of recycling is considerably larger than the net glycolytic flux or the activity of the oxidative pentose-phosphate cycle.
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Affiliation(s)
- W D Hatzfeld
- Lehrstuhl für Pflanzenphysiologie, Universität Bayreuth, D-8580, Bayreuth, Germany
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27
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Beaudry RM, Severson RF, Black CC, Kays SJ. Banana ripening: implications of changes in glycolytic intermediate concentrations, glycolytic and gluconeogenic carbon flux, and fructose 2,6-bisphosphate concentration. PLANT PHYSIOLOGY 1989; 91:1436-44. [PMID: 16667198 PMCID: PMC1062203 DOI: 10.1104/pp.91.4.1436] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
In ripening banana (Musa sp. [AAA group, Cavendish subgroup] cv Valery) fruit, the concentration of glycolytic intermediates increased in response to the rapid conversion of starch to sugars and CO(2). Glucose 6-phosphate (G-6-P), fructose 6-phosphate (Fru 6-P), and pyruvate (Pyr) levels changed in synchrony, increasing to a maximum one day past the peak in ethylene synthesis and declining rapidly thereafter. Fructose 1,6-bisphosphate (Fru 1,6-P(2)) and phosphoenolpyruvate (PEP) levels underwent changes dissimilar to those of G 6-P, Fru 6-P, and Pyr, indicating that carbon was regulated at the PEP/Pyr and Fru 6-P/Fru 1,6-P(2) interconversion sites. During the climacteric respiratory rise, gluconeogenic carbon flux increased 50- to 100-fold while glycolytic carbon flux increased only 4- to 5-fold. After the climacteric peak in CO(2) production, gluconeogenic carbon flux dropped dramatically while glycolytic carbon flux remained elevated. The steady-state fructose 2,6-bisphosphate (Fru 2,6-P(2)) concentration decreased to (1/2) that of preclimacteric fruit during the period coinciding with the rapid increase in gluconeogenesis. Fru 2,6-P(2) concentration increased thereafter as glycolytic carbon flux increased relative to gluconeogenic carbon flux. It appears likely that the initial increase in respiration in ripening banana fruit is due to the rapid influx of carbon into the cytosol as starch is degraded. As starch reserves are depleted and the levels of intermediates decline, the continued enhancement of respiration may, in part, be maintained by an increased steady-state Fru 2,6-P(2) concentration acting to promote glycolytic carbon flux at the step responsible for the interconversion of Fru 6-P and Fru 1,6-P(2).
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Affiliation(s)
- R M Beaudry
- Department of Horticulture, University of Georgia, Athens, Georgia 30602
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Mahajan R, Singh R. Properties of Pyrophosphate:Fructose-6-Phosphate Phosphotransferase from Endosperm of Developing Wheat (Triticum aestivum L.) Grains. PLANT PHYSIOLOGY 1989; 91:421-6. [PMID: 16667036 PMCID: PMC1062009 DOI: 10.1104/pp.91.1.421] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Pyrophosphate:fructose-6-phosphate phosphotransferase (PFP, EC 2.7.1.90) from endosperm of developing wheat (Triticum aestivum L.) grains was purified to apparent homogeneity with about 52% recovery using ammonium sulfate fractionation, ion exchange chromatography on DEAE-cellulose and gel filtration through Sepharose-CL-6B. The purified enzyme, having a molecular weight of about 170,000, was a dimer with subunit molecular weights of 90,000 and 80,000, respectively. The enzyme exhibited maximum activity at pH 7.5 and was highly specific for pyrophosphate (PPi). None of the nucleoside mono-, di- or triphosphate could replace PPi as a source of energy and inorganic phosphate (Pi). Similarly, the enzyme was highly specific for fructose-6-phosphate. It had a requirement for Mg(2+) and exhibited hyperbolic kinetics with all substrates including Mg(2+). K(m) values as determined by Lineweaver-Burk plots were 322, 31, 139, and 129 micromolar, respectively, for fructose-6-phosphate, PPi, fructose-1,6-bisphosphate and Pi. Kinetic constants were determined in the presence of fructose-2,6-bisphosphate, which stimulated activity about 20-fold and increased the affinity of the enzyme for its substrates. Initial velocity studies indicated kinetic mechanism to be sequential. At saturating concentrations of fructose-2,6-bisphosphate (1 micromolar), Pi strongly inhibited PFP; the inhibition being mixed with respect to both fructose-6-phosphate and PPi, with K(i) values of 0.78 and 1.2 millimolar, respectively. The inhibition pattern further confirmed the mechanism to be sequential with random binding of the substrates. Probable role of PFP in endosperm of developing wheat grains (sink tissues) is discussed.
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Affiliation(s)
- R Mahajan
- Department of Chemistry and Biochemistry, Haryana Agricultural University, Hisar-125 004, India
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Häusler RE, Holtum JA, Latzko E. Cytosolic phosphofructokinase from spinach leaves : I. Purification, characteristics, and regulation. PLANT PHYSIOLOGY 1989; 90:1498-505. [PMID: 16666957 PMCID: PMC1061917 DOI: 10.1104/pp.90.4.1498] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Cytosolic ATP-dependent phosphofructokinase (PFK) from spinach leaves (Spinacia oleracea L.) was enriched 2600-fold by (NH(4))(2)SO(4) fractionation, DEAE anion exchange chromatography, Blue Sepharose CL-6B, and ATP agarose type 3-affinity chromatography. The final preparation had a specific activity of 417 nkat per milligram protein and exhibited four bands between 50 and 70 kilodaltons following denaturing electrophoresis. Only one band of ATP- and fructose 6-phosphate (F-6-P)-dependent, Pistimulated activity was detected following isoelectric focusing PAGE and nondenaturing discontinuous PAGE of the final preparation. Crude extracts contained, in addition to the band observed in the final preparation, a second band that was inhibited by Pi. The latter band is presumably chloroplastic PFK. PFK was stimulated by the anions Pi(2-), Cl(-), SO(4) (2-), NO(3) (-), HAsO(4) (2-), and HCO(3) (-) but was not affected by NH(4) (+). Pi and Mg(2+) changed the response of PFK toward pH and affected the saturation kinetics of F-6-P. In general, activity was highest when Pi was high and (or) Mg(2+) was low. Phosphoenolpyruvate (PEP), 2-PGA, and PPi, but not 3-PGA, inhibited PFK. Although the inhibition by PEP and 2-PGA was reduced or relieved by Pi, the inhibition by PPi was not affected by Pi. F-2, 6-P(2) had no effect upon the activity of PFK. It is proposed that, in the cytosol of spinach leaves, PFK is likely to be more active during the dark, when cytosolic Pi levels are high, than in the light.
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Affiliation(s)
- R E Häusler
- Botanisches Institut der Westfälischen Wilhelms-Universität, Schlossgarten 3, D-4400 Münster, Federal Republic of Germany
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Kiss F, Johnson TC, Klecan AL, Vincze G, Buchanan BB, Balogh A. Identification of two forms of PFK and a fructose-2,6-bisphosphate independent form of PFP in a green alga. PHOTOSYNTHESIS RESEARCH 1989; 21:123-128. [PMID: 24424531 DOI: 10.1007/bf00033366] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/06/1988] [Accepted: 10/17/1988] [Indexed: 06/03/2023]
Abstract
Cell-free preparations from the green alga, Chlorella pyrenoidosa, contained two forms of phosphofructokinase (PFK), designated PFK I and PFK II. This represents the first evidence for a second form of PFK in green algae. A pyrophosphate D-fructose-6-phosphate, 1-phosphotransferase (PFP) activity, that was unaffected by the regulatory metabolite, fructose-2,6-bisphosphate, co-purified with PFK II through several steps. The data suggest that Chlorella pyrenoidosa resembles higher plants in containing two forms of PFK, but differs in containing an atypical form of PFP.
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Affiliation(s)
- F Kiss
- Department of Biology and Chemistry, György Bessenyei College, Nyiregyháza, Hungary
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31
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Servaites JC, Fondy BR, Li B, Geiger DR. Sources of Carbon for Export from Spinach Leaves throughout the Day. PLANT PHYSIOLOGY 1989; 90:1168-74. [PMID: 16666868 PMCID: PMC1061860 DOI: 10.1104/pp.90.3.1168] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Rates of net carbon exchange, export, starch, and sucrose synthesis were measured in leaves of spinach (Spinacia oleracea L.) throughout a 14-hour period of sinusoidal light to determine the sources of carbon contributing to export. Net carbon exchange rate closely followed light level, but export remained relatively constant throughout the day. In the morning when photosynthesis was low, starch degradation provided most of the carbon for export, while accumulated sucrose was exported during the evening. At high photosynthesis rate, the regulatory metabolite fructose 2,6-bisphosphate was low, allowing more of the newly fixed carbon to flow to sucrose through cytosolic fructose bisphosphatase. When the rate of sucrose synthesis exceeded the rate of export from the leaf, sucrose accumulated and soon thereafter sucrose synthesis declined. A decreasing sucrose synthesis rate resulted in additional carbon moving to the synthesis of starch, which was maintained throughout the remainder of the day. The declining sucrose synthesis rate coincided with decreasing activity of sucrose phosphate synthase present in gel-filtered leaf extracts. A rise in the leaf levels of uridine diphosphoglucose and fructose 6-phosphate throughout the day was consistent with this declining activity.
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Affiliation(s)
- J C Servaites
- Department of Biology, University of Dayton, Dayton, Ohio 45469
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Phelps DC, McDonald RE. Changes in Fructose 2,6-Bisphosphate Levels in Green Pepper (Capsicum annuum L.) Fruit in Response to Temperature. PLANT PHYSIOLOGY 1989; 90:458-62. [PMID: 16666793 PMCID: PMC1061746 DOI: 10.1104/pp.90.2.458] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
The regulatory metabolite, fructose 2,6-bisphosphate (Fru 2,6-P(2)) was found in green pepper (Capsicum annuum L.). The Fru 2,6-P(2) level was found to: (a) rise rapidly in response to heat; (b) drop rapidly, followed by recovery, in response to cold storage of fruit and, (c) oscillate during cold storage of fruit. The possible existence of a relationship between chilling injury and Fru 2,6-P(2) is considered.
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Affiliation(s)
- D C Phelps
- U.S. Department of Agriculture, Agricultural Research Service, Orlando, Florida 32803
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Carnal NW, Black CC. Soluble Sugars as the Carbohydrate Reserve for CAM in Pineapple Leaves : Implications for the Role of Pyrophosphate:6-Phosphofructokinase in Glycolysis. PLANT PHYSIOLOGY 1989; 90:91-100. [PMID: 16666775 PMCID: PMC1061682 DOI: 10.1104/pp.90.1.91] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Neutral ethanol-soluble sugar pools serve as carbohydrate reserves for Crassulacean acid metabolism (CAM) in pineapple (Ananas comosus (L.) Merr.) leaves. Levels of neutral soluble sugars and glucans fluctuated reciprocally with concentrations of malic acid. Hexose loss from neutral soluble-sugar pools was sufficient to account for malic acid accumulation with about 95% of the required hexose accounted for by turnover of fructose and glucose pools. Hexose loss from starch or starch plus lower molecular weight glucan pools was insufficient to account for nocturnal accumulation of malic acid. The apparent maximum catalytic capacity of pyrophosphate:6-phosphofructokinase (PPi-PFK) at 15 degrees C was about 16 times higher than the mean maximum rate of glycolysis that occurred to support malic acid accumulation in pineapple leaves at night and 12 times higher than the mean maximum rate of hexose turnover from all carbohydrate pools. The apparent maximum catalytic capacity of ATP-PFK at 15 degrees C was about 70% of the activity required to account for the mean maximal rate of hexose turnover from all carbohydrate pools if turnover were completely via glycolysis, and marginally sufficient to account for mean maximal rates of acidification. Therefore, at low night temperatures conducive to CAM and under subsaturating substrate concentrations, PPi-PFK activity, but not ATP-PFK activity, would be sufficient to support the rate of glycolytic carbohydrate processing required for acid accumulation. These data for pineapple establish that there are at least two types of CAM plants with respect to the nature of the carbohydrate reserve utilized to support nighttime CO(2) accumulation. The data further indicate that the glycolytic carbohydrate processing that supports acidification proceeds in different subcellular compartments in plants utilizing different carbohydrate reserves.
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Affiliation(s)
- N W Carnal
- Department of Biology, San Francisco State University, San Francisco, California 94132
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Smeekens S, Macdonald FD, Buchanan BB. Studies on the entry of fructose-2,6-bisphosphate into chloroplasts. PLANT PHYSIOLOGY 1989; 89:1270-4. [PMID: 16666695 PMCID: PMC1056007 DOI: 10.1104/pp.89.4.1270] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
The regulatory metabolite fructose-2,6-bisphosphate (Fru-2,6-P(2)) has an important function in controlling the intermediary carbon metabolism of leaves. Fru-2,6-P(2) controls two cytosolic enzymes involved in the interconversion of fructose-6-phosphate and fructose-1,6-bisphosphate (fructose-1,6-bisphosphatase and pyrophosphate, fructose-6-phosphate 1-phosphotransferase) and thereby controls the partitioning of photosynthate between sucrose and starch. It has been demonstrated that Fru-2,6-P(2) is present mainly in the cytosol. Here we present evidence that Fru-2,6-P(2) can be taken up by isolated intact chloroplasts but at a very slow rate (about 0.01 micromoles per milligram of chlorophyll per hour). This uptake is time and concentration dependent and is inhibited by PPi. When provided a physiological concentration of Fru-2,6-P(2) (10 micromolar), chloroplasts accumulated up to 0.6 micromolar Fru-2,6-P(2) in the stroma. Elevated plastid Fru-2,6-P(2) levels had no effect on overall photosynthetic rates of isolated chloroplasts. The results indicate that, while Fru-2,6-P(2) enters isolated chloroplasts at a sluggish rate, caution should be exercised in ascribing physiological importance to effects of Fru-2,6-P(2) on chloroplast enzymes.
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Affiliation(s)
- S Smeekens
- Division of Molecular Plant Biology, University of California, Hilgard Hall, Berkeley California 94720
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35
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Stitt M. Product inhibition of potato tuber pyrophosphate:fructose-6-phosphate phosphotransferase by phosphate and pyrophosphate. PLANT PHYSIOLOGY 1989; 89:628-33. [PMID: 16666593 PMCID: PMC1055892 DOI: 10.1104/pp.89.2.628] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
The product inhibition of potato (Solanum tuberosum) tuber pyrophosphate:fructose-6-phosphate phosphotransferase by inorganic pyrophosphate and inorganic phosphate has been studied. The binding of substrates for the forward (glycolytic) and the reverse (gluconeogenic) reaction is random order, and occurs with only weak competition between the substrate pair fructose-6-phosphate and pyrophosphate, and between the substrate pair fructose-1,6-bisphosphate and phosphate. Pyrophosphate is a powerful inhibitor of the reverse reaction, acting competitively to fructose-1,6-biphosphate and noncompetitively to phosphate. At the concentrations needed for catalysis of the reverse reaction, phosphate inhibits the forward reaction in a largely noncompetitive mode with respect to both fructose-6-phosphate and pyrophosphate. At higher concentrations, phosphate inhibits both the forward and the reverse reaction by decreasing the affinity for fructose-2,6-bisphosphate and thus, for the other three substrates. These results allow a model to be proposed, which describes the interactions between the substrates at the catalytic site. They also suggest the enzyme may be regulated in vivo by changes of the relation between metabolites and phosphate and could act as a means of controlling the cytosolic pyrophosphate concentration.
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Affiliation(s)
- M Stitt
- Lehrstuhl für Pflanzenphysiologie, Universität Bayreuth, 8580 Bayreuth, Federal Republic of Germany
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Servaites JC, Geiger DR, Tucci MA, Fondy BR. Leaf Carbon Metabolism and Metabolite Levels during a Period of Sinusoidal Light. PLANT PHYSIOLOGY 1989; 89:403-8. [PMID: 16666556 PMCID: PMC1055854 DOI: 10.1104/pp.89.2.403] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Photosynthesis rate, internal CO(2) concentration, starch, sucrose, and metabolite levels were measured in leaves of sugar beet (Beta vulgaris L.) during a 14-h period of sinusoidal light, which simulated a natural light period. Photosynthesis rate closely followed increasing and decreasing light level. Chloroplast metabolite levels changed in a manner indicating differential activation of enzymes at different light levels. Starch levels declined during the first and last 2 hours of the photoperiod, but increased when photosynthesis rate was greater than 50% of maximal. Sucrose and sucrose phosphate synthase levels were constant during the photoperiod, which is consistent with a relatively steady rate of sucrose synthesis during the day as observed previously (BR Fondy et al. [1989] Plant Physiol 89: 396-402). When starch was being degraded, glucose 1-phosphate level was high and there was a large amount of glucose 6-phosphate above that in equilibrium with fructose 6-phosphate, while fructose 6-phosphate and triose-phosphate levels were very low. Likewise, the regulatory metabolite, fructose, 2,6-bisphosphate was high, indicating that little carbon could move to sucrose from starch by the triose-phosphate pathway. These data cast doubt upon the feasibility of significant carbon flow through the triose-phosphate pathway during starch degradation and support the need for an additional pathway for mobilizing starch carbon to sucrose.
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Affiliation(s)
- J C Servaites
- Department of Biology, University of Dayton, Dayton, Ohio 45469
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Corbineau F, Carmignac DF, Gahan PB, Maple AJ. Glycolytic activity in embryos of Pisum sativum and of non-dormant or dormant seeds of Avena sativa L. expressed through activities of PFK and PPi-PFK. HISTOCHEMISTRY 1989; 90:359-64. [PMID: 2541117 DOI: 10.1007/bf00508313] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
A quantitative cytochemical assay for PPi-PFK activity in the presence of Fru-2,6-P2 is described along with its application to determine levels of activity in embryos of Pisum sativum and Avena sativa. The activity of ATP-PFK has also been studied in parallel as have PFK activities during the switch from dormant to non-dormant embryos in Avena sativa. PPi-PFK activity has been demonstrated in all tissues of Pisum sativum embryos and of Avena sativa embryos including the scutellum and the aleurone layers. The PPi-PFK activity was greater than that of ATP-PFK in both dormant and non-dormant seeds though with only marginally more activity in the dormant as opposed to the non-dormant state.
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Affiliation(s)
- F Corbineau
- Laboratoire de Physiologie des Organes Végétaux après Récolte, C.N.R.S., Meudon, France
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Soulie JM, Riviere M, Ricard J. Enzymes as biosensors. 2. Hysteretic response of chloroplastic fructose-1,6-bisphosphatase to fructose 2,6-bisphosphate. EUROPEAN JOURNAL OF BIOCHEMISTRY 1988; 176:111-7. [PMID: 2843363 DOI: 10.1111/j.1432-1033.1988.tb14257.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Oxidized chloroplastic fructose-bisphosphatase is almost totally inactive at pH 7.5, that is under pH conditions that prevail in the chloroplast stroma. When preincubated for different time periods with fructose 2,6-bisphosphate and assayed in the absence of this ligand, it displays an activity which is directly related to the duration of the preincubation phase. This implies that fructose 2,6-bisphosphate induces enzyme conformers that appear in sequence and may be competent for catalytic activity. Upon desorption of fructose 2,6-bisphosphate the enzyme may retain its active conformation for a time period whose duration depends on magnesium concentration. It thus appears that reduction of the enzyme is not an obligatory prerequisite for its activity. Fructose 2,6-bisphosphate behaves as a competitive inhibitor of the reduced, active enzyme, with respect to the real substrate. When assayed with the oxidized enzyme, however, it behaves as an activator. Moreover the apparent steady-state rate that may be measured experimentally depends on both fructose 2,6-bisphosphate concentration and the direction of a concentration change. The reaction velocity experimentally measured is thus a meta-steady-state rate and depends on the initial conditions of the system. The fructose-bisphosphatase system thus displays, with respect to fructose 2,6-bisphosphate, a hysteresis loop and may then sense whether the concentration of that ligand is increased or decreased. A model has been proposed which allows one to explain these results. This model is based on the view that the substrate and fructose 2,6-bisphosphate compete for the same site of the enzyme and that this latter ligand stabilizes a conformation competent for enzyme activity. After the ligand has been chased away, the enzyme retains the active conformation for a while and slowly relapses to the initial inactive conformation. The time-scale of this slow relaxation overlaps that of the steady state of product appearance and this generates meta-steady-state kinetics, which is dependent on the initial state and therefore on the history of the system.
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Affiliation(s)
- J M Soulie
- Centre de Biochimie et de Biologie Moléculaire du CNRS, Marseille, France
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Steingraber M, Outlaw WH, Hampp R. Subcellular compartmentation of fructose 2,6-bisphosphate in oat mesophyll cells. PLANTA 1988; 175:204-208. [PMID: 24221713 DOI: 10.1007/bf00392428] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/25/1987] [Accepted: 02/10/1988] [Indexed: 06/02/2023]
Abstract
Evacuolated mesophyll protoplasts from oat (Avena sativa L.) were fractionated by a membrane-filtration technique. This method of rapid quenching of metabolic reactions permitted estimation of the in-vivo pools of fructose 2,6-bisphosphate (Fru2,6bisP) in the cytosol, chloroplasts and mitochondria. Vacuolar Fru2,6bisP was calculated as the difference between control protoplasts and evacuolated ones. The results indicate that Fru2,6bisP is exclusively cytosol-located in oat mesophyll protoplasts. Assuming a cytosolic volume of about 2 pl per evacuolated protoplast, the cytosolic concentration there was 11 μM if protoplasts were in darkness. Illumination of either control or evacuolated protoplasts resulted in a significant decrease in the Fru2,6bisP content within 5 min.
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Affiliation(s)
- M Steingraber
- Institut für Biologie I der Universität Tübingen, Auf der Morgenstelle 1, D-7400, Tübingen, Federal Republic of Germany
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Kerbel EL, Kader AA, Romani RJ. Effects of Elevated CO(2) Concentrations on Glycolysis in Intact ;Bartlett' Pear Fruit. PLANT PHYSIOLOGY 1988; 86:1205-9. [PMID: 16666055 PMCID: PMC1054652 DOI: 10.1104/pp.86.4.1205] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Mature intact ;Bartlett' pear fruit (Pyrus communis L.) were stored under a continuous flow of air or air + 10% CO(2) for 4 days at 20 degrees C. Fruit kept under elevated CO(2) concentrations exhibited reduced respiration (O(2) consumption) and ethylene evolution rates, and remained firmer and greener than fruit stored in air. Protein content, fructose 1,6-bisphosphate levels, and ATP:phosphofructokinase and PPi:phosphofructokinase activities declined, while levels of fructose 6-phosphate and fructose 2,6-bisphosphate increased in fruit exposed to air + 10% CO(2). These results are discussed in light of a possible inhibitory effect of CO(2) at the site of action of both phosphofructokinases in the glycolytic pathway, which could account, at least in part, for the observed reduction in respiration.
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Affiliation(s)
- E L Kerbel
- Department of Pomology, University of California, Davis California 95616
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41
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Mullen JA, Koller HR. Trends in carbohydrate depletion, respiratory carbon loss, and assimilate export from soybean leaves at night. PLANT PHYSIOLOGY 1988; 86:517-21. [PMID: 16665939 PMCID: PMC1054516 DOI: 10.1104/pp.86.2.517] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
To evaluate assimilate export from soybean (Glycine max [L.] Merrill) leaves at night, rates of respiratory CO(2) loss, specific leaf weight loss, starch mobilization, and changes in sucrose concentration were measured during a 10-hour dark period in leaves of pod-bearing ;Amsoy 71' and ;Wells II' plants in a controlled environment. Lateral leaflets were removed at various times between 2200 hours (beginning dark period) and 0800 hours (ending dark period) for dry weight determination and carbohydrate analyses. Respiratory CO(2) loss was measured throughout the 10-hour dark period. Rate of export was estimated from the rate of loss in specific leaf weight and rate of CO(2) efflux. Rate of assimilate export was not constant. Rate of export was relatively low during the beginning of the dark period, peaked during the middle of the dark period, and then decreased to near zero by the end of darkness. Rate of assimilate export was associated with rate of starch mobilization and amount of starch reserves available for export. Leaves of Amsoy 71 had a higher maximum export rate in conjunction with a greater total change in starch concentration than did leaves of Wells II. Sucrose concentration rapidly declined during the first hour of darkness and then remained constant throughout the rest of the night in leaves of both cultivars. Rate of assimilate export was not associated with leaf sucrose concentration.
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Affiliation(s)
- J A Mullen
- Department of Agronomy, Purdue University, West Lafayette, Indiana 47907
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42
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Keleti T, Ovádi J. Control of metabolism by dynamic macromolecular interactions. CURRENT TOPICS IN CELLULAR REGULATION 1988; 29:1-33. [PMID: 3293924 DOI: 10.1016/b978-0-12-152829-4.50003-3] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Affiliation(s)
- T Keleti
- Institute of Enzymology, Biological Research Center, Hungarian Academy of Sciences, Budapest
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43
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Plaut Z, Mayoral ML, Reinhold L. Effect of altered sink: source ratio on photosynthetic metabolism of source leaves. PLANT PHYSIOLOGY 1987; 85:786-91. [PMID: 16665777 PMCID: PMC1054339 DOI: 10.1104/pp.85.3.786] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
When seven crop species were grown under identical environmental conditions, decreased sink:source ratio led to a decreased photosynthetic rate within 1 to 3 days in Cucumis sativus L., Gossypium hirsutum L., and Raphanus sativus L., but not in Capsicum annuum L., Solanum melongena L., Phaseolus vulgaris L., or Ricinus communis L. The decrease was not associated with stomatal closure. In cotton and cucumber, sink removal led to an increase in starch and sugar content, in glucose 6-phosphate and fructose 6-phosphate pools, and in the proportion of (14)C detected in sugar phosphates and UDPglucose following (14)CO(2) supply. When mannose was supplied to leaf discs to sequester cytoplasmic inorganic phosphate, promotion of starch synthesis, and inhibition of CO(2) fixation, were observed in control discs, but not in discs from treated plants. Phosphate buffer reduced starch synthesis in the latter, but not the former discs. The findings suggest that sink removal led to a decreased ratio inorganic phosphate:phosphorylated compounds. In beans (14)C in sugar phosphates increased following sink removal, but without sucrose accumulation, suggesting tighter feedback control of sugar level. Starch accumulated to higher levels than in the other plants, but CO(2) fixation rate was constant for several days.
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Affiliation(s)
- Z Plaut
- Institute of Soils and Water Agricultural Research Organization P.O. Box 6, Bet Dagan 50-250, Israel
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44
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Kobza J, Edwards GE. The photosynthetic induction response in wheat leaves: net CO2 uptake, enzyme activation, and leaf metabolites. PLANTA 1987; 171:549-59. [PMID: 24225719 DOI: 10.1007/bf00392305] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/27/1986] [Accepted: 03/24/1987] [Indexed: 05/13/2023]
Abstract
The photosynthetic induction response was studied in whole leaves of wheat (Triticum aestivum L.) following 5-min, 30-min and 10-h dark periods. After the 5-min dark treatment there was a rapid burst in the rate of photosynthesis upon illumination (half of maximum after 30s), followed by a slight decrease after 1.5 more min and then a gradual rise to the maximum rate. During this initial burst in photosynthesis, there was a rapid rise in the level of 3-phosphoglycerate (PGA) and a high PGA/triose-phosphate (triose-P) ratio was obtained. In addition, after the 5-min dark treatment, ribulose-1,5-bisphosphate carboxylase (Rubisco, EC 4.1.1.39), ribulose-5-phosphate kinase (EC 2.7.1.19) and chloroplastic fructose-1,6-bisphosphatase (EC 3.1.3.11) maintained a relatively high state of activation, and maximum activation occurred within 1 min of illumination. The results indicate there is a high capacity for CO2 fixation in the cycle upon illumination but attaining maximum rates requires an increase in the ribulose-1,5-bisphosphate (RuBP) pool (adjustment in triose-P utilization for carbohydrate synthesis versus RuBP synthesis). With both the 30-min and 10-h dark pretreatments there was only a slight rise in photosynthesis upon illumination, followed by a lag, then a gradual increase to steady-state (half-maximum rate after 6 min). In contrast to the 5-min dark treatment, the level of PGA was low and actually decreased initially, whereas the level of RuBP increased and was high during induction, indicating that Rubisco is limiting. This regulation via the carboxylase was not reflected in the initial extractable activity, which reached a maximum by 1 min after illumination. The light activation of chloroplastic fructose-1,6-bisphosphatase in leaves darkened for 30 min and 10 h prior to illumination was relatively slow (reaching a maximum after 8 min). However, this was not considered to limit carbon flux through the carbon-fixation cycle during induction since RuBP was not limiting. When photosynthesis approached the maximum steady-state rate, a high PGA/triose-P ratio and a high PGA/RuBP ratio were obtained. This may allow a high rate of photosynthesis by producing a favorable mass-action ratio for the reductive phase (the conversion of PGA to triose phosphate) while stimulating starch and sucrose synthesis.
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Affiliation(s)
- J Kobza
- Department of Botany, Washington State University, 99164-4230, Pullman, WA, USA
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45
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Häusler RE, Holtum JA, Latzko E. Cytosolic ATP-Dependent Phosphofructokinase from Spinach. PLANT PHYSIOLOGY 1987; 84:205-7. [PMID: 16665416 PMCID: PMC1056556 DOI: 10.1104/pp.84.2.205] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
ATP-dependent 6-phosphofructokinase (PFK) activity is present in both chloroplastic and in nonchloroplastic fractions isolated from spinach protoplasts. The activity in the extra-chloroplastic fraction was stimulated 2- to 3.5-fold by 25 mm inorganic phosphate (Pi), the chloroplast-associated activity was inhibited 2- to 5-fold. The Pi stimulated activity was ATP-dependent and was not an artifact due to the presence of fructose 6-P, Pi, pyrophosphatase, and pyrophosphate fructose 6-P 1-phosphotransferase (PFP). PFK activities, which expressed characteristics similar to those separated from protoplasts, could be separated following ammonium sulfate fractionation of crude extracts; the ammonium sulfate treatment also separated both PFK activities from PFP. It is concluded that spinach leaves contain a cytosolic PFK. This activity is relatively stable, is stimulated by Pi over a wide pH range, is not a result of the transformation of another enzyme activity, and has an activity that is similar to, or slightly less than, that of the cytosolic PFP.
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Affiliation(s)
- R E Häusler
- Botanisches Institut, Westfälische Wilhelms-Universität, Schlossgarten 3, 4400 Münster, Federal Republic of Germany
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Botha FC, Small JG. Comparison of the Activities and Some Properties of Pyrophosphate and ATP Dependent Fructose-6-Phosphate 1-Phosphotransferases of Phaseolus vulgaris Seeds. PLANT PHYSIOLOGY 1987; 83:772-7. [PMID: 16665337 PMCID: PMC1056448 DOI: 10.1104/pp.83.4.772] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
THE DISTRIBUTION OF PYROPHOSPHATE: fructose 6-phosphate phosphotransferase (PFP) and ATP: fructose-6-phosphate 1-phosphotransferase (PFK) was studied in germinating bean (Phaseolus vulgaris cv Top Crop) seeds. In the cotyledons the PFP activity was comparable with that of PFK. However, in the plumule and radicle plus hypocotyl, PFP activity exceeds that of PFK. Approximately 70 to 90%, depending on the stage of germination, of the total PFP and PFK activities were present in the cotyledons. Highest specific activity of both enzymes, however, occurred in the radicle plus hypocotyl (64-90 nanomoles.min.milligram protein). Fractionation studies indicate that 40% of the total PFK activity was associated with the plastids while PFP is apparently confined to the cytoplasm. The cytosolic isozyme of PFK exhibits hyperbolic kinetics with respect to fructose 6-P and ATP with K(m) values of 320 and 46 micromolar, respectively. PFP also exhibits hyperbolic kinetics both in the presence and absence of the activator fructose-2,6-P(2). The activation is caused by lowering the K(m) for fructose 6-P from 18 to 1.1 millimolar and that for pyrophosphate (PPi) from 40 to 25 micromolar, respectively. Levels of fructose 2,6-P(2) and PPi in the seeds are sufficient to activate PFP and thereby enable a glycolytic role for PFP during germination. However, the fructose 6-P content appears to be well below the K(m) of PFP for this compound and would therefore preferentially bind to the catalytic site of PFK, which has a lower K(m) for fructose 6-P. The ATP content appears to be at saturating levels for PFK.
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Affiliation(s)
- F C Botha
- Department of Botany, University of The Orange Free State, Bloemfontein 9300, Republic of South Africa
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Salminen SO, Streeter JG. Uptake and Metabolism of Carbohydrates by Bradyrhizobium japonicum Bacteroids. PLANT PHYSIOLOGY 1987; 83:535-40. [PMID: 16665284 PMCID: PMC1056400 DOI: 10.1104/pp.83.3.535] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Bradyrhizobium japonicum bacteroids were isolated anaerobically and were supplied with (14)C-labeled trehalose, sucrose, UDP-glucose, glucose, or fructose under low O(2) (2% in the gas phase). Uptake and conversion of (14)C to CO(2) were measured at intervals up to 90 minutes. Of the five compounds studied, UDP-glucose was most rapidly absorbed but it was very slowly metabolized. Trehalose was the sugar most rapidly converted to CO(2), and fructose was respired at a rate at least double that of glucose. Sucrose and glucose were converted to CO(2) at a very low but measurable rate (<0.1 nanomoles per milligram protein per hour). Carbon Number 1 of glucose appeared in CO(2) at a rate 30 times greater than the conversion of carbon Number 6 to CO(2), indicating high activity of the pentose phosphate pathway. Enzymes of the Entner-Doudoroff pathway were not detected in bacteroids, but very low activities of sucrose synthase and phosphofructokinase were demonstrated. Although metabolism of sugars by B. japonicum bacteroids was clearly demonstrated, the rate of sugar uptake was only 1/30 to 1/50 the rate of succinate uptake. The overall results support the view that, although bacteroids metabolize sugars, the rates are very low and are inadequate to support nitrogenase.
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Affiliation(s)
- S O Salminen
- Department of Agronomy, The Ohio State University, Wooster, Ohio 44691
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49
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Cadet F, Meunier JC, Ferté N. Effects of pH and fructose 2,6-bisphosphate on oxidized and reduced spinach chloroplastic fructose-1,6-bisphosphatase. EUROPEAN JOURNAL OF BIOCHEMISTRY 1987; 162:393-8. [PMID: 3026809 DOI: 10.1111/j.1432-1033.1987.tb10614.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
This report describes the effects of pH and fructose 2,6-bisphosphate (an analog of fructose 1,6-bisphosphate) on the activity of oxidized and reduced fructose-1,6-bisphosphatase from spinach chloroplasts. Studies were carried out with either fructose 1,6-bisphosphate, the usual substrate, or sedoheptulose 1,7-bisphosphate, an alternative substrate. The reduction of the oxidized enzyme is achieved by a thiol/disulfide interchange. The pK values relative to each redox form for the same substrate (either fructose 1,6-bisphosphate or sedoheptulose 1,7-bisphosphate) are identical, suggesting the same site for both substrates on the active molecule. The finding that the analog (fructose 2,6-bisphosphate) behaves like a competitive inhibitor for both substrates also favours this hypothesis. The inhibitory effect of this sugar is more important when the enzyme is reduced than when it is oxidized. The shift in the optimum pH observed when [Mg2+] was raised is interpreted as a conformational change of oxidized enzyme demonstrated by a change in fluorescence. The reduced and oxidized forms have the same theoretical rates relative to both substrates, but the reduced form has an observed Vmax which is 60% of the theoretical Vmax while that of the oxidized form is only 37% of the theoretical Vmax. The reduced enzyme appears more efficient than the oxidized one in catalysis.
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Brown D, Kershaw KA. Isolation and Characterization of Two Enzymes Capable of Hydrolyzing Fructose-1,6-Bisphosphatase from the Lichen Peltigera rufescens. PLANT PHYSIOLOGY 1986; 82:462-7. [PMID: 16665052 PMCID: PMC1056141 DOI: 10.1104/pp.82.2.462] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Two enzymes capable of hydrolyzing fructose-1,6-bisphosphate (FBP) have been isolated from the foliose lichen Peltigera rufescens (Weis) Mudd. These enzymes can be separated using Sephadex G-100 and DEAE Sephacel chromatography. One enzyme has a pH optimum of 6.5, and a substrate affinity of 228 micromolar FBP. This enzyme does not require MgCl(2) for activity, and is inhibited by AMP. The second enzyme has a pH optimum of 9.0, with no activity below pH 7.5. This enzyme responds sigmoidally to Mg(2+), with half-saturation concentration of 2.0 millimolar MgCl(2), and demonstrates hyperbolic kinetics for FBP (K(m) = 39 micromolar). This enzyme is activated by 20 millimolar dithiothreitol, is inhibited by AMP, but is not affected by fructose-2-6-bisphosphate. It is hypothesized that the latter enzyme is involved in the photosynthetic process, while the former enzyme is a nonspecific acid phosphatase.
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Affiliation(s)
- D Brown
- Department of Biology, McMaster University, Hamilton, Ontario, Canada L8S 4K1
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