Phosphoglucomutase. V. Multiple forms of phosphoglucomutase

Enzymatic characterization and validation of gene expression of phosphoglucomutase from Cordyceps militaris

The purification and characterization of PGM (Phosphoglucomutase) from Cordyceps militaris (C. militaris) was investigated. PGM was purified using a combination of ultrafiltration, salting-out and ion exchange chromatography resulting in 4.23-fold enhancement of activity with a recovery of 20.01%. Molecular mass was 50.01 kDa by SDS-PAGE. The optimal activity was achieved at pH 7.5 and 30 °C with NADPH as substrate. The results showed that SDS, DTT Li⁺, Cu²⁺, Na⁺, Mn²⁺ and Al³⁺ were effective PGM inhibitors; whereas glycerol, Zn²⁺, Mg²⁺, Ca²⁺, Fe²⁺ and Fe³⁺ could enhance the activity of PGM, and the K_m and V_max values were 11.62 mmol/L and 416.67 U/mL, respectively. At the same time, qRT-PCR was used to test the changes of mRNA transcription level of PGM gene encoding under two fermentation conditions: basic medium and optimized medium. The relative quantitative results of PGM target genes resulting in 2.60-fold enhancement than the control group.

Identification of isoforms of the exocytosis-sensitive phosphoprotein PP63/parafusin in Paramecium tetraurelia and demonstration of phosphoglucomutase activity

PP63 (parafusin) is a 63 kDa phosphoprotein which is very rapidly (within 80 ms) dephosphorylated (to P63) during triggered trichocyst exocytosis; this occurs selectively in exocytosis-competent Paramecium tetraurelia strains. In the present work, two cDNAs coding for PP63/parafusin have been isolated, one of which is a new isoform. These isoforms are 99.6% identical and are derived from two different genes. Similarity searches revealed 43-51% identity of the deduced amino acid sequences with known phosphoglucomutases from yeast and mammals. The sequences of two proteolytic peptides obtained from PP63/parafusin isolated from Paramecium are identical to parts of the amino acid sequence deduced from the major cDNA. The major cDNA was mutated from the macronuclear ciliate genetic code into the universal genetic code and expressed in Escherichia coli. The recombinant protein shows the same biochemical and immunological characteristics as the (P)P63/parafusin originally isolated from Paramecium. It has the same specific phosphoglucomutase activity as phosphoglucomutase from chicken muscle. We also show that recombinant P63-1 parafusin 1 is a substrate of an endogenous casein kinase from Paramecium, as is the originally isolated P63/parafusin. Polyclonal antibodies against recombinant P63-1/parafusin 1 were raised which recognized phosphoglucomutases from different sources. Thus we show that PP63/parafusin and phosphoglucomutase in Paramecium are identical.

A 63 kDa phosphoprotein undergoing rapid dephosphorylation during exocytosis in Paramecium cells shares biochemical characteristics with phosphoglucomutase

We have enriched phosphoglucomutase (PGM; EC 5.4.2.2) approximately 20-fold from Paramecium tetraurelia cells by combined fractional precipitation with (NH4)2SO4, gel filtration and anion-exchange chromatography yielding two PGM peaks. Several parameters affecting PGM enzymic activity, molecular mass and pI were determined. Phosphorylation studies were done with isolated endogenous protein kinases. Like the 63 kDa phosphoprotein PP63, which is dephosphorylated within 80 ms during synchronous trichocyst exocytosis [Höhne-Zell, Knoll, Riedel-Gras, Hofer and Plattner (1992) Biochem. J. 286, 843-849], PGM has a molecular mass of 63 kDa and forms of identical pI. Since mammalian PGM activity depends on the presence of glucose 1,6-bisphosphate (Glc-1,6-P2) (which is lost during anion-exchange chromatography), we analysed this aspect with Paramecium PGM. In this case PGM activity was shown not to be lost, due to p-nitrophenyl phosphate-detectable phosphatase(s) (which we have separated from PGM), but also due to loss of Glc-1,6-P2. Like PGM from various vertebrate species, PGM activity from Paramecium can be fully re-established by addition of Glc-1,6-P2 at 10 nM, and it is also stimulated by bivalent cations and insensitive to chelating or thiol reagents. The PGM which we have isolated can be phosphorylated by endogenous cyclic-GMP-dependent protein kinase or by endogenous casein kinase. This results in three phosphorylated bands of identical molecular mass and pI values, as we have shown to occur with PP63 after phosphorylation in vivo (forms with pI 6.05, 5.95, 5.85). In ELISA, antibodies raised against PGM from rabbit skeletal muscle were reactive not only with original PGM but also with PGM fractions from Paramecium. Therefore, PGM and PP63 seem to be identical with regard to widely different parameters, i.e. co-elution by chromatography, molecular mass, phosphorylation by the two protein kinases tested, pI values of isoforms, and immuno-binding. Recent claims that PP63 ('parafusin') would not be identical with PGM specifically in Paramecium are critically evaluated. Since some glycolytic enzymes are discussed as being associated with the Ca(2+)-release channel in muscle sarcoplasmic reticulum, and since sub-plasmalemmal Ca2+ stores in Paramecium closely resemble sarcoplasmic reticulum, a possible function of PP63/PGM in exocytosis regulation is discussed, particularly since dephosphorylation strictly parallels exocytosis.

Measurement of glucuronidation by isolated rat liver cells using [14C]fructose

We have developed a simple and sensitive method for the study of the relative rates of glucuronidation of compounds, in isolated liver cells, based on the incorporation of 14C from fructose into glucuronide conjugates. Liver cells from fasted rats are used to minimize any reduction of the specific activity by glycogenolysis. Although rates of glucuronidation are lower in isolated liver cells from fasted rats than in those from fed rats, because of a reduction in the concentration of UDP-glucuronic acid, it is possible to compare the rates of glucuronidation of different compounds. Radiolabelled glucuronides are separated from [14C]fructose and [14C]glucose, produced by the liver cells, by normal-phase HPLC on a polar amino-cyano column. The specific activity of the glucuronide was found to be approximately 50% of that of the [14C]fructose. Absolute amounts of glucuronide can be determined by measuring the specific activity of the [14C]glucose, also produced by liver cells from fructose, which reflects that of the glucose-6-phosphate and hence the UDP-glucuronic acid used for glucuronidation, although for the measurement of relative rates this would not be necessary. We have used this method to examine the kinetics of the glucuronidation of N-acetyl-p-aminophenol (acetaminophen), 4-nitrophenol and 1-naphthol in isolated rat liver cells. The method should be applicable to the study of the rates of glucuronidation of a range of aglycones and, unlike other methods, does not require glucuronide standards or radiolabelled aglycone.

Purification and partial characterization of the phosphoglucomutase isozymes from human placenta

We have developed a simple procedure for the purification of phosphoglucomutase (PGM) isozymes from human placenta of healthy women. The technique involves the ammonium sulfate fractionation, ion-exchange and dye-ligand chromatographies. By this method we obtained homogeneous isozyme preparations of the products ("primary" and "secondary") of the two PGM1 and PGM2 loci. The final specific activities were 1134.6-1441.8 units/mg for PGM1 forms and 40.2-46.5 units/mg for PGM2 forms. On SDS-polyacrylamide gel electrophoresis analysis, the final preparations gave a single protein band of 58,500 and 69,000 Mr for PGM1 and PGM2 isozymes, respectively. These forms have the same kinetic properties, but from the substrate specificity experiments we have found that PGM2 forms are more effective for catalyzing the phosphoribomutase and glucose 1,6-bisphosphate synthase reaction than PGM1 forms. All these properties are shared by the same isozymes previously isolated from human erythrocytes but in this procedure the use of human placenta for the PGM isozymes purification takes advantage of high specific activity of PGM in the extracts of this tissue as well as obtaining highly homogeneous protein suitable for studies at molecular level.

Transcription of a yeast phosphoglucomutase isozyme gene is galactose inducible and glucose repressible

The Saccharomyces cerevisiae GAL5 (PGM2) gene was isolated and shown to encode the major isozyme of phosphoglucomutase. Northern (RNA) blot hybridization revealed that the GAL5 transcript level increased three- to fourfold in response to galactose and was severely repressed in response to glucose. Total cellular phosphoglucomutase activity was likewise responsive to galactose and to glucose, and this responsiveness was found to be due primarily to variation in the activity of the major isozyme of phosphoglucomutase. These results imply that the major and minor isozymes of phosphoglucomutase have distinct roles in yeast cells. The galactose inducibility of GAL5 was found to be under the control of the GAL4, GAL80, and GAL3 genes. In striking contrast to other galactose-inducible genes, the GAL5 gene exhibited an unusually high GAL4-independent basal level of expression. These results have implications for metabolic trafficking.

Transcription of a yeast phosphoglucomutase isozyme gene is galactose inducible and glucose repressible

The Saccharomyces cerevisiae GAL5 (PGM2) gene was isolated and shown to encode the major isozyme of phosphoglucomutase. Northern (RNA) blot hybridization revealed that the GAL5 transcript level increased three- to fourfold in response to galactose and was severely repressed in response to glucose. Total cellular phosphoglucomutase activity was likewise responsive to galactose and to glucose, and this responsiveness was found to be due primarily to variation in the activity of the major isozyme of phosphoglucomutase. These results imply that the major and minor isozymes of phosphoglucomutase have distinct roles in yeast cells. The galactose inducibility of GAL5 was found to be under the control of the GAL4, GAL80, and GAL3 genes. In striking contrast to other galactose-inducible genes, the GAL5 gene exhibited an unusually high GAL4-independent basal level of expression. These results have implications for metabolic trafficking.

Biochemical characterization of genotypes at the phosphoglucomutase-2 locus in the Pacific oyster, Crassostrea gigas

The four most common allozymes at the Pgm-2 locus in Crassostrea gigas were purified and characterized over physiological ranges of temperature and pH. Significant differences were observed between genotypes in their apparent Michaelis constants for glucose-1-phosphate and glucose-1,6-diphosphate, V max/Km ratios, pH-dependent activities, and temperature stabilities. These functional differences were caused almost exclusively by the divergent properties of the Pgm-292 allozyme; limited differentiation existed among the Pgm-296, Pgm-2100, and Pgm-2104 variants. Heterozygotes displayed strict intermediacy for all kinetic and structural properties examined. The results are discussed in light of their ability to account for the overdominant body weights of Pgm-2 heterozygotes reported by Fujio (1982). It is concluded that overdominance is unlikely to arise at this locus as a consequence of these biochemical differences because of their limited magnitude and incompatibility with allelic frequencies in natural populations.

Isoenzymes of phosphoglucomutase from human red blood cells: isolation and kinetic properties

A procedure has been developed for the purification of phosphoglucomutase from human red cell (phenotype PGM1 a1 or a3) lysates. It yields homogeneous isoenzyme preparations of the products ("primary" and "secondary") of the two PGM1 and PGM2 loci with distinctive pI (from 6.07 to 5.29). There are substantial differences between PGM1 and PGM2 isoenzymes, having single polypeptide chains of 58,500 and 69,000 Mr respectively and showing different thermostability. The kinetic properties of all the isoenzymes for the phosphoglucomutase reaction are essentially the same (apart from the specific activity of 1089-1263 units/mg for PGM1 forms vs 37-42 units/mg for PGM2 forms), but there are striking differences in substrate specificity. In fact the products of PGM1 locus are "true" phosphoglucomutases, being specific to mutate glucose monophosphates, whereas the PGM2 forms also display phosphoribomutase and glucose 1,6-bisphosphate synthetic activities. Some kinetic properties of these "side activities" are also reported.

Ferritin: a zinc detoxicant and a zinc ion donor

Rats were injected with 1 mg of Zn2+ as zinc sulfate or 2 mg of Cd2+ as cadmium sulfate per kg of body weight on a daily basis. After seven injections, ferritin and metallothionein were isolated from the livers of the rats. Significant amounts of zinc were associated with ferritin. Incubation of such ferritin with apoenzymes of calf intestinal alkaline phosphatase, yeast phosphoglucomutase, and yeast aldolase restored their enzymic activity. The amount of zinc injected was insufficient to stimulate significant synthesis of metallothionein, but similar experiments with injection of cadmium did stimulate the synthesis of metallothionein. The amount of Zn2+ in ferritin of Cd-injected rats was greater than that in ferritin in Zn-injected rats, which was greater than that in ferritin of normal rats. Thus at comparable protein concentration ferritin from Cd-injected rats was a better Zn2+ donor than was ferritin from Zn-injected or normal animals. Ferritin is a normal constituent of several tissues, whereas metallothionein is synthesized under metabolic stress. Thus ferritin may function as a "metal storage and transferring agent" for iron and for zinc. It is suggested that ferritin probably serves as the initial chelator for Zn2+ and perhaps other metal ions as well and that under very high toxic levels of metal ions the synthesis of metallothionein is initiated as the second line of defense.

Properties of the two common electrophoretic variants of phosphoglucomutase in Drosophila melanogaster

Phosphoglucomutase (PGM) of adult stage in Drosophilia melanogaster has been characterized by gel filtration, ion-exchange chromatography, and isoelectric focusing. The two common electrophoretic variants, PGMA and PGMB, differ with respect to their kinetic and stability parameters. PGMA is more thermostable than PGMB but shows the same pH optimum, equal dependence on Mg2+, and identical molecular weight. There is no significant kinetic difference between the two allozymes at the optimum pH values, but at pH 6.0 the Km value for glucose-1,6-diphosphate of PGMB is significantly higher than that of PGMA. This difference might explain the observed selective advantage of the PgmA allele in population studies.

Properties and intracellular distribution of two phosphoglucomutases from spinach leaves

Two isoenzymes of phosphoglucomutase from spinach (Spinacia oleracea L.) leaves can be separated by ammonium-sulfate gradient solubilization or DEAE-cellulose ion exchange chromatography. They were designated as phosphoglucomutase 1 and 2, according to decreasing electrophoretic mobility towards the anode at pH 8.9. Phosphoglucomutase 1 is localized in the stroma of the chloroplasts, phosphoglucomutase 2 is a cytosolic enzyme as judged from aqueous cell fractionation studies. Both isoenzymes have very similar properties such as dependence on MgCl2, pH activity profile, and Km for glucose-1-phosphate and glucose-1,6-bisphosphate. From sedimentation-velocity analysis a molecular weight of 60,000 was estimated for either isoenzyme.

Purification and properties of phosphoglucomutase from Fleischmann's yeast

1. A procedure has been described for the purification of the major isozyme of yeast phosphoglucomutase of highest known specific activity. 2. The native enzyme has a molecular weight of about 65400 and was found to be homogeneous as judged by sucrose density gradient centrifugation, gel filtration, electrophoresis on acrylamide gel and ultracentrifugal analysis. In the presence of denaturing agents such as guanidine hydrochloride or sodium dodecyl sulfate, the enzyme dissociated into 32000-molecular-weight subunits. 3. As isolated, the enzyme has one mole of phosphate bound per mole of enzyme. Preparations incubated with 1.0 mM EDTA in 10 mM citrate buffer, pH 5.5 and dialysed against 10 mM metal-free citrate buffer, pH 5.5, contain no intrinsically bound Zn2+ and were enzymically inactive but fully active in the presence of 5 mM Mg2+ and 84% as active with 0.5 mM Zn2+. Simultaneous presence of both ions at these concentrations did not enhance activity. Enzyme was completely and irreversibly inactivated by preincubation with Be2+. Inactive enzyme had one mole of Be2+ bound per mole of enzyme. 4. Enzyme exhibited "ping-pong" kinetics rather than "random sequential". Km values for glucose 1-phosphate and for glucose 1,6-bisphosphate were calculated to be 2.34 times 10(-5) M and 2.24 times 10(-6) M, respectively. Rate of enzyme phosphate turnover was studied with rapid-mixing technique. The rates of 32P release from 32P-labeled enzyme and its appearance as glucose 6-[32P]phosphate were comparable and remained unaffected by addition of glucose 1,6-bisphosphate.

Phosphoglucomutase mutants of Neurospora sitophila and their relation to morphology

Biochemical and genetic evidence is presented that the rg-1 and rg-2 genes control the structure of the two isozymes of phosphoglucomutase (Phosphoglucomutase I and II) in Neurospora silophila. Results of kinetic and gel filtration studies show that the two phosphoglucomutases may exist in vitro either as separate or as a single but complex molecular species depending on the ionic concentration. The complex phosphoglucomutase molecule is suggested to be the physiologically active form of the enzyme. The change in the enzyme structure is discussed in relation to the morphological change in the ragged mutant strains.

The nature of isoenzymes

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The effect of dietary and hormonal conditions on the activities of glycolytic enzymes in rat epididymal adipose tissue

1. Measurements were made of the activities of nine glycolytic enzymes in epididymal adipose tissues obtained from rats that had undergone one of the following treatments: starvation; starvation followed by re-feeding with bread or high-fat diet; feeding with fat without preliminary starvation; alloxan-diabetes; alloxan-diabetes followed by insulin therapy. 2. In general, the activities of the glycolytic enzymes of adipose tissue, unlike those of liver, were not greatly affected by the above treatments. 3. The ;key' glycolytic enzymes, phosphofructokinase and pyruvate kinase, were generally no more adaptive in response to physiological factors than other glycolytic enzymes such as glucose phosphate isomerase, fructose diphosphate aldolase, triose phosphate isomerase, glycerol 3-phosphate dehydrogenase, phosphoglycerate kinase and lactate dehydrogenase. 4. Adiposetissue pyruvate kinase did not respond to feeding with fat in a manner similar to the liver enzyme. 5. Glyceraldehyde phosphate dehydrogenase had a behaviour pattern unlike the other eight glycolytic enzymes studied in that its activity was depressed by feeding with fat and was not restored to normal by re-feeding with a high-fat diet after starvation. These results are discussed in relation to the requirements of adipose tissue for glycerol phosphate in the esterification of fatty acids. 6. A statistical analysis of the results permitted the writing of linear equations describing the relationships between the activities of eight of the enzymes studied. 7. Evidence is presented for the existence of two constant-proportion groups amongst the enzymes studied, namely (i) glucose phosphate isomerase, phosphoglycerate kinase and lactate dehydrogenase, and (ii) triose phosphate isomerase, fructose diphosphate aldolase and pyruvate kinase. 8. Mechanisms for maintaining the observed relationships between the activities of the enzymes in the tissue are discussed.

Electrophoretic variants of phosphoglucomutase in Saccharomyces species

Strains of Saccharomyces cerevisiae and species with which S. cerevisiae is interfertile display a characteristic pattern of electrophoretic variants of phosphoglucomutase (PGM) consisting of a major component and one or two minor components, all of which migrate toward the cathode. The patterns are consistent with an earlier finding that two unlinked genes, one of which has two known alleles, determine the synthesis of PGM in S. cerevisiae. The PGM patterns of strains of S. fragilis, S. lactis, and S. marxianus, species thought to be closely related to each other and only distantly related to S. cerevisiae, also displayed a characteristic pattern of PGM variants, but it was quite different from that of S. cerevisiae. In these species five or six electrophoretic variants could be detected, all of which migrated toward the anode. We interpret the differences in the PGM variants of the two groups of species as a reflection of differences in genetic composition which have arisen in two phylogenetically distinct groups that have become sexually isolated from each other.

Genetic control of phosphoglucomutase variants in Saccharomyces cerevisiae

The three electrophoretic variants of phosphoglucomutase in Saccharomyces cerevisiae breeding stocks are produced by two unlinked genes, pgm-1 and pgm-2; pgm-1 contains two known alleles, pgm-1a and pgm-1b, each of which specifies a minor phosphoglucomutase component, and pgm-2 specifies the major phosphoglucomutase component.