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Dermcidin expression in hepatic cells improves survival without N-glycosylation, but requires asparagine residues. Br J Cancer 2006; 94:1663-71. [PMID: 16685272 PMCID: PMC2361319 DOI: 10.1038/sj.bjc.6603148] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Proteolysis-inducing factor, a cachexia-inducing tumour product, is an N-glycosylated peptide with homology to the unglycosylated neuronal survival peptide Y-P30 and a predicted product of the dermcidin gene, a pro-survival oncogene in breast cancer. We aimed to investigate whether dermcidin is pro-survival in liver cells, in which proteolysis-inducing factor induces catabolism, and to determine the role of potentially glycosylated asparagine residues in this function. Reverse cloning of proteolysis-inducing factor demonstrated ∼100% homology with the dermcidin cDNA. This cDNA was cloned into pcDNA3.1+ and both asparagine residues removed using site-directed mutagenesis. In vitro translation demonstrated signal peptide production, but no difference in molecular weight between the products of native and mutant vectors. Immunocytochemistry of HuH7 cells transiently transfected with V5-His-tagged dermcidin confirmed targeting to the secretory pathway. Stable transfection conferred protection against oxidative stress. This was abrogated by mutation of both asparagines in combination, but not by mutation of either asparagine alone. These findings suggest that dermcidin may function as an oncogene in hepatic as well as breast cells. Glycosylation does not appear to be required, but the importance of asparagine residues suggests a role for the proteolysis-inducing factor core peptide domain.
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2
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Increased expression of several components of the ATP dependant proteosome pathway in denervated rat muscle is reversed by beta 2-adrenergic agonists. Biochem Soc Trans 1998; 26:S311. [PMID: 10047825 DOI: 10.1042/bst026s311] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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3
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Skeletal muscle myocytes undergo protein loss and reactive oxygen-mediated NF-kappaB activation in response to tumor necrosis factor alpha. FASEB J 1998; 12:871-80. [PMID: 9657527 DOI: 10.1096/fasebj.12.10.971] [Citation(s) in RCA: 148] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Skeletal muscle atrophy and weakness are thought to be stimulated by tumor necrosis factor alpha (TNF-alpha) in a variety of chronic diseases. However, little is known about the direct effects of TNF-alpha on differentiated skeletal muscle cells or the signaling mechanisms involved. We have tested the effects of TNF-alpha on the mouse-derived C2C12 muscle cell line and on primary cultures from rat skeletal muscle. TNF-alpha treatment of differentiated myotubes stimulated time- and concentration-dependent reductions in total protein content and loss of adult myosin heavy chain (MHCf) content; these changes were evident at low TNF-alpha concentrations (1-3 ng/ml) that did not alter muscle DNA content and were not associated with a decrease in MHCf synthesis. TNF-alpha activated binding of nuclear factor kappaB (NF-kappaB) to its targeted DNA sequence and stimulated degradation of I-kappaBalpha, an NF-kappaB inhibitory protein. TNF-alpha stimulated total ubiquitin conjugation whereas a 26S proteasome inhibitor (MG132 10-40 microM) blocked TNF-alpha activation of NF-kappaB. Catalase 1 kU/ml inhibited NF-kappaB activation by TNF-alpha; exogenous hydrogen peroxide 200 microM activated NF-kappaB and stimulated I-kappaBalpha degradation. These data demonstrate that TNF-alpha directly induces skeletal muscle protein loss, that NF-kappaB is rapidly activated by TNF-alpha in differentiated skeletal muscle cells, and that TNF-alpha/NF-kappaB signaling in skeletal muscle is regulated by endogenous reactive oxygen species.
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5
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Anabolic effects of a range of beta 2-adrenoceptor agonists in a clonal G8.P8 cell line. Biochem Soc Trans 1996; 24:214S. [PMID: 8736872 DOI: 10.1042/bst024214s] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
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6
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Low levels of glucose-6-phosphate hydrolysis in the sarcoplasmic reticulum of skeletal muscle: involvement of glucose-6-phosphatase. Mol Membr Biol 1996; 13:103-8. [PMID: 8839454 DOI: 10.3109/09687689609160583] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Glucose-6-phosphate hydrolysis was measured in a fraction obtained from rabbit fast-twitch skeletal muscle and corresponding to total sarcoplasmic reticulum, as well as in three subfractions containing longitudinal tubules, terminal cisternae or both structures. In all cases the levels of hydrolysis measured both in native and disrupted membranes were approximately 60-100 times lower than the microsomal glucose-6-phosphatase activity of the corresponding livers. In contrast to liver microsomes, most (up to 80%) of the glucose-6-phosphate hydrolysing activity in muscle sarcoplasmic reticulum membranes was not inactivated by pH 5.0 pre-incubation indicating that it was not catalysed by the specific glucose-6-phosphatase enzyme. Osmotically induced changes in light-scattering intensity of sarcoplasmic reticulum vesicles revealed that, in contrast to liver microsomes, sarcoplasmic reticulum vesicles were not selectively permeable to glucose-6-phosphate as mannose-6-phosphate was also permeable and in addition they were poorly permeable to glucose. Immunoblot experiments using antibodies raised against the glucose-6-phosphatase enzyme, and liver endoplasmic reticulum glucose and Pi translocases, failed to detect the presence of these protein components in sarcoplasmic reticulum membranes. Southern blot analysis of reverse transcriptase-polymerase chain reaction products from rat muscle revealed that glucose-6-phosphatase mRNA is present in muscle. Quantification of Northern blot analysis of liver and muscle mRNA indicated that muscle contains less than 2% of the amount of glucose-6-phosphate mRNA found in corresponding livers. We conclude that very low levels of specific glucose-6-phosphatase (e.g. as in liver; E.C. 3.1.3.9) are present in muscle sarcoplasmic reticulum and that the muscle and liver glucose-6-phosphatase systems have several different properties.
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7
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An altered T2 beta translocase of the glucose-6-phosphatase system in the membrane of the endoplasmic reticulum from livers of Ehrlich-ascites-tumour-bearing mice. Biochem J 1995; 311 ( Pt 2):537-40. [PMID: 7487892 PMCID: PMC1136032 DOI: 10.1042/bj3110537] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The inhibitory interactions of orthophosphate (P1) with the glucose-6-phosphatase system of intact microsomes derived from the livers of normal and Ehrlich-ascites-tumour-bearing mice reveal the appearance of a novel form of the T2 beta translocase component of the glucose-6-phosphatase system in tumour-stressed mice. Kinetic studies, with and without 20 mM P1, show a strictly classical competitive inhibition, with a K1,P1 of 4.2 mM, with disrupted microsomes from both control and tumour-bearing mouse liver. Inhibition was also observed with intact microsomes from livers of control mice, and contributions by both competitive and non-competitive components of inhibition were quantified by calculation of Kis,P1 and Kii,P1 values respectively. However, little inhibition was noted with intact microsomes from the livers of tumour-bearing mice. It is concluded that this novel form of T2 beta is less able to transport Pi, from the cytosol to the endoplasmic reticulum lumen, perhaps because of the tumour-related increased Km for Pi transport in this direction.
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Abstract
The entry of substrates into, and the export of glururonides from, the lumen of hepatic endoplasmic reticulum (ER) in vitro (sealed microsomes) has been measured using radioactivity-labelled materials and a rapid filtration assay. Analysis of liver microsomes from a jaundiced patient showed the accumulation of bilirubin glucuronides within the lumen of the ER. Further analysis of these hepatic microsomes revealed that newly synthesized 1-naphthol glucuronide could exit from the microsomes whereas bilirubin glucuronide was accumulated within the microsomes. These results suggest the existence of mechanisms for the sorting of small molecules, destined for export through bile canalicular or basolateral plasma membranes, by ER. Furthermore, these sorting processes may be regulated by specific transporters within the ER.
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9
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Abstract
To examine the effects of the presence of Ehrlich ascites tumours on both the catalytic unit and the substrate/product translocase components of the glucose-6-phosphatase system in vivo, we isolated microsomes from the livers of control and tumour-bearing mice. Samples were analysed immunochemically for the quantity of catalytic unit, stabilizing protein and translocases T2 and T3 proteins. In comparison experiments, a variety of kinetic studies were performed. The most striking findings in tumour-bearing mice were: a 2.5-fold increase in the quantity of translocase T2 protein; increases in the Km and Vmax. for glucose 6-phosphate phosphohydrolase; and a decrease in the Km value for carbamoyl phosphate (carbamoyl-P) of carbamoyl-P:glucose phosphotransferase, all with intact microsomes. The percentage latency at Vmax. decreased for PPi phosphohydrolase and for glucose 6-phosphate phosphohydrolase, but was unaffected for carbamoyl-P:glucose phosphotransferase. These observations support a tumour-related increase in translocase T2 capacity in vivo, as it transports Pi from the microsomal lumen to the medium and carbamoyl-P or PPi from the medium to the microsomal lumen.
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11
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Diagnosis of the genetic deficiencies of each of the proteins of the multicomponent glucose-6-phosphatase system. Biochem Soc Trans 1993; 21:34S. [PMID: 8383611 DOI: 10.1042/bst021034s] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
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12
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Identification, purification and genetic deficiencies of the glucose-6-phosphatase system transport proteins. Eur J Pediatr 1993; 152 Suppl 1:S14-7. [PMID: 8391441 DOI: 10.1007/bf02072081] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Hepatic microsomal glucose-6-phosphatase (Glc-6-P'ase) is a complex multicomponent system containing at least three transport proteins, in addition to the catalytic subunit and a Ca2+ binding regulatory protein. The transport proteins have been designated T1 the glucose-6-phosphate transport protein, T2 a phosphate/pyrophosphate transport protein and T3 a glucose transport protein. Diagnosis of the genetic deficiencies of these transport proteins at present requires a complex kinetic analysis of the Glc-6-P'ase system as a whole. Here we describe the progress to date in our attempts to identify, purify and clone each transport protein with the ultimate aim of isolating specific cDNA probes for each transport protein which can be used for the diagnosis of types 1b, 1c and the putative 1d glycogen storage diseases.
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The molecular basis of the genetic deficiencies of five of the components of the glucose-6-phosphatase system: improved diagnosis. Eur J Pediatr 1993; 152 Suppl 1:S18-21. [PMID: 8391442 DOI: 10.1007/bf02072082] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The understanding of type 1 glycogen storage diseases (GSDs) has been greatly hindered by a lack of knowledge of the molecular basis of glucose-6-phosphatase (Glc-6-P'ase). The problem has been the complete failure of many laboratories, including our own, to purify to homogeneity a single polypeptide with high levels of Glc-6-P'ase activity. The best preparations to date all contain five or six different polypeptide bands and have specific activities in the range 17-50 mumoles/min per milligram. The two major reasons for failure have been that Glc-6-P'ase is extremely difficult to solubilise from the microsomal membrane (large amounts of detergents are needed) and that it is not a single polypeptide as originally thought, but a multicomponent system. Recent studies of patients with type 1 GSD have proved that Glc-6-P'ase comprises at least five different polypeptides. Four of the proteins have now been purified and three have been cloned. We have assayed the Glc-6-P'ase system in over 600 human biopsy samples and developed microassays to diagnose deficiencies of each of the proteins. Ways of avoiding possible problems which have the potential to lead to the wrong diagnosis will be discussed.
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14
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Abstract
1. The existence of specific glucose-6-phosphatase activity in human intestinal mucosa has been somewhat controversial. 2. We have demonstrated the presence of low levels of specific glucose-6-phosphatase activity in normal human adult intestinal mucosa. Activity was found in oesophagus, stomach, duodenum and colon. 3. Immunoblot analysis using antibodies monospecific for the 36.5 kDa liver glucose-6-phosphatase catalytic subunit demonstrated that intestinal mucosa contains low levels of the glucose-6-phosphatase enzyme protein. 4. The low levels of activity together with problems of proteolysis make human intestinal biopsies unsuitable for use in the diagnosis of type 1 glycogen-storage disease.
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15
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Cloning and expression of a hepatic microsomal glucose transport protein. Comparison with liver plasma-membrane glucose-transport protein GLUT 2. Biochem J 1992; 286 ( Pt 1):173-7. [PMID: 1520266 PMCID: PMC1133035 DOI: 10.1042/bj2860173] [Citation(s) in RCA: 92] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Antibodies raised against a 52 kDa rat liver microsomal glucose-transport protein were used to screen a rat liver cDNA library. Six positive clones were isolated. Two clones were found to be identical with the liver plasma-membrane glucose-transport protein termed GLUT 2. The sequence of the four remaining clones indicates that they encode a unique microsomal facilitative glucose-transport protein which we have termed GLUT 7. Sequence analysis revealed that the largest GLUT 7 clone was 2161 bp in length and encodes a protein of 528 amino acids. The deduced amino acid sequence of GLUT 7 shows 68% identity with the deduced amino acid sequence of rat liver GLUT 2. The GLUT 7 sequence is six amino acids longer than rat liver GLUT 2, and the extra six amino acids at the C-terminal end contain a consensus motif for retention of membrane-spanning proteins in the endoplasmic reticulum. When the largest GLUT 7 clone was transfected into COS 7 cells the expressed protein was found in the endoplasmic reticulum and nuclear membrane, but not in the plasma membrane. Microsomes isolated from the transfected COS 7 cells demonstrated an increase in their microsomal glucose-transport capacity, demonstrating that the GLUT 7 clone encodes a functional endoplasmic-reticulum glucose-transport protein.
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16
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Regulation of hepatic microsomal glucose transport. Biochem Soc Trans 1992; 20:238S. [PMID: 1330765 DOI: 10.1042/bst020238s] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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17
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Microsomes isolated from oviductal tissue contain low levels of the specific glucose-6-phosphatase system. Biochem Soc Trans 1992; 20:294S. [PMID: 1330778 DOI: 10.1042/bst020294s] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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18
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Glycogen storage disease diagnosed in adults. THE QUARTERLY JOURNAL OF MEDICINE 1992; 82:207-22. [PMID: 1321455] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Glycogen storage diseases are usually identified in childhood. We present the clinical, biochemical and histological features of 10 patients first diagnosed in adult life. Five had glycogen storage disease type 1a, one type 1c, two type IX, and in two patients there were previously unreported abnormalities of hepatic glucose-6-phosphatase system activity. Of the latter, one patient had an inhibitor of liver glucose-6-phosphatase (pseudo-1b glycogen storage disease) the other having abnormal glucose-6-phosphatase activity and microsomal pyrophosphate transport. A glucagon test is suggested as a useful screening procedure. Glycogen storage disease should be considered in adults with symptoms suggesting hypoglycaemia.
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Analysis of human hepatic microsomal glucose-6-phosphatase in clinical conditions where the T2 pyrophosphate/phosphate transport protein is absent. Biochem J 1992; 281 ( Pt 3):859-63. [PMID: 1311177 PMCID: PMC1130768 DOI: 10.1042/bj2810859] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The availability of a rare set of human hepatic microsomes in which T2, a pyrophosphate/phosphate transport protein of the glucose-6-phosphatase system, has been shown immunologically to be completely absent, has permitted further characterization of multicomponent glucose-6-phosphatase (EC 3.1.3.9). Pyrophosphatase activity in intact microsomes was found to be totally absent, but was normal in disrupted microsomes. However, Pi did not accumulate within the lumen of the microsomes when glucose 6-phosphate was the substrate. This was not as predicted if there is only one transport protein in the endoplasmic reticulum capable of transporting Pi, produced by glucose-6-phosphatase, out of the lumen. The results suggest that the pyrophosphate/phosphate transport system of human hepatic endoplasmic reticulum must be more complex than previously thought, as it must comprise at least two protein components.
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20
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The molecular basis of the hepatic microsomal glucose-6-phosphatase system. BIOCHIMICA ET BIOPHYSICA ACTA 1991; 1092:129-37. [PMID: 1850300 DOI: 10.1016/0167-4889(91)90146-o] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
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21
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Identification and characterization of a hepatic microsomal glucose transport protein. T3 of the glucose-6-phosphatase system? Biochem J 1991; 275 ( Pt 2):363-7. [PMID: 1850983 PMCID: PMC1150061 DOI: 10.1042/bj2750363] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
A 52 kDa polypeptide in rat liver microsomes was identified as a glucose-binding protein by its ability to weakly bind cytochalasin B and by its cross-reactivity to an antibody raised against the human erythrocyte glucose transport protein. The microsomal glucose binding polypeptide was purified by affinity chromatography and an antibody was raised against it. The inhibitory effect of this antibody on rat microsomal glucose-6-phosphatase activity and on glucose transport out of microsomal vesicles indicates that this protein is a microsomal glucose transport protein.
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22
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Abstract
Antibodies raised against purified components of glucose-6-phosphatase were used to study the transmembrane orientation of the complex. Measurements of glucose-6-phosphatase activities and immunoblot analysis of sealed microsomes and detergent-solubilized microsomes after treatment with proteases suggested that most of the catalytic subunit resides within the lumen of the endoplasmic reticulum. In contrast, other components of glucose-6-phosphatase are accessible to the cytoplasm. Treatment of the partially purified glucose-6-phosphatase enzyme with glycopeptide N-glycosidase indicated that the catalytic subunit of the enzyme was a glycoprotein.
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Kinetic and immunologic evidence for the absence of glucose-6-phosphatase in early human chorionic villi and term placenta. BIOCHIMICA ET BIOPHYSICA ACTA 1991; 1073:161-7. [PMID: 1846754 DOI: 10.1016/0304-4165(91)90197-o] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The existence of the enzyme glucose-6-phosphatase (G6Pase) in early and term human placenta was investigated by comparing the characteristics of placental microsomal glucose 6-phosphate (G6P) hydrolytic activity and liver G6Pase. Placental microsomes exhibited similar apparent Km values for G6P and beta-glycerophosphate in intact and deoxycholate-treated microsomes, heat stability at acidic pH, low latency of mannose 6-phosphate hydrolysis, very low activity of pyrophosphate: glucose phosphotransferase, and undetectable [U-14C]G6P transport into the placental microsomes, all of which indicated that specific G6Pase activity does not exist in placenta. Immunological evidence of the absence of both 36.5 kDa and T2 proteins, which represent the G6Pase catalytic protein and the phosphate/pyrophosphate transporter protein, respectively, confirmed that early and term human placenta are devoid of the multicomponent G6Pase enzyme.
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24
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Activation of hepatic microsomal glucose-6-phosphate transport by prostaglandins. Biochem Soc Trans 1990; 18:1252-3. [PMID: 2088897 DOI: 10.1042/bst0181252] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
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25
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Activation of glucose-6-phosphatase in intact hepatic microsomes. Biochem J 1990; 270:839-40. [PMID: 2173555 PMCID: PMC1131813 DOI: 10.1042/bj2700839] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
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26
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The ontogeny of human hepatic microsomal glucose-6-phosphatase proteins. Clin Chem 1990; 36:1633-7. [PMID: 2170061] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
We have studied 250 human liver biopsy samples to determine the ontogeny of the microsomal glucose-6-phosphatase (EC 3.1.3.9) system. Human hepatic glucose-6-phosphatase enzyme activity develops at 11 weeks' gestation and slowly increases to approximately 10% of adult activity at term. In the first week after birth, activity rises to adult values. Increases in enzyme activity coincide with increasing concentrations of the glucose-6-phosphatase enzyme protein. The phosphate/pyrophosphate transport protein (T2) of the human hepatic glucose-6-phosphatase complex develops at a different rate from that of the enzyme. Our study shows that the development of rat and human glucose-6-phosphatase activities are completely different. We conclude that deficiencies of the proteins in the microsomal glucose-6-phosphatase complex can be diagnosed with much more certainty perinatally than prenatally.
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27
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Abstract
Abstract
We have studied 250 human liver biopsy samples to determine the ontogeny of the microsomal glucose-6-phosphatase (EC 3.1.3.9) system. Human hepatic glucose-6-phosphatase enzyme activity develops at 11 weeks' gestation and slowly increases to approximately 10% of adult activity at term. In the first week after birth, activity rises to adult values. Increases in enzyme activity coincide with increasing concentrations of the glucose-6-phosphatase enzyme protein. The phosphate/pyrophosphate transport protein (T2) of the human hepatic glucose-6-phosphatase complex develops at a different rate from that of the enzyme. Our study shows that the development of rat and human glucose-6-phosphatase activities are completely different. We conclude that deficiencies of the proteins in the microsomal glucose-6-phosphatase complex can be diagnosed with much more certainty perinatally than prenatally.
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Abstract
The effects of Ca2+ on the microsomal glucose-6-phosphatase activity were investigated. Evidence is provided that increases by Ca2+ in both the pyrophosphatase and the glucose-6-phosphate-hydrolysing activities are due to an increase in microsomal transport capacity of T2, the phosphate/pyrophosphate-transport protein.
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30
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Glucose-6-phosphatase activity in fed rat liver. Biochem J 1990; 266:619-20. [PMID: 2156503 PMCID: PMC1131178] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
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31
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32
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A direct method for the diagnosis of human hepatic type 1b and type 1c glycogen-storage disease. Clin Sci (Lond) 1989; 76:573-9. [PMID: 2544342 DOI: 10.1042/cs0760573] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
1. Type 1b and type 1c glycogen-storage disease are caused respectively by deficiencies of the glucose-6-phosphate translocase and the phosphate/pyrophosphate translocase of the human hepatic microsomal glucose-6-phosphatase system. 2. Current methods of unequivocally diagnosing type 1b and type 1c glycogen storage disease are indirect and complex. 3. We have therefore developed a simple, rapid and direct microfiltration assay for the glucose-6-phosphate translocase and the phosphate/pyrophosphate translocase. 4. We have demonstrated that the microfiltration assay can be used to directly diagnose type 1b and 1c glycogen-storage disease in microsomes isolated from hepatic needle-biopsy samples.
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Abstract
Microsomes isolated from adult human gall-bladders have for the first time been shown to contain specific glucose-6-phosphatase activity. The gall-bladder glucose-6-phosphatase enzyme has the same molecular weight (36,500 daltons) and similar immunological properties and kinetic characteristics to the hepatic microsomal glucose-6-phosphatase enzyme.
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35
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Abstract
The glucose-6-phosphatase enzyme protein of the human hepatic microsomal glucose-6-phosphatase system was identified as a 36.5 kDa polypeptide. The 36.5 kDa glucose-6-phosphatase enzyme protein was shown to be absent in the microsomes isolated from a patient previously diagnosed as having a type 1a glycogen storage disease.
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36
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Abstract
Microsomal fractions isolated from pancreatic islet cells were shown to contain high specific glucose-6-phosphatase activity. The islet-cell glucose-6-phosphatase enzyme has the same Mr (36,500), similar immunological properties and kinetic characteristics to the hepatic microsomal glucose-6-phosphatase enzyme.
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37
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The identification of T2; the phosphate/pyrophosphate transport protein of the hepatic microsomal glucose-6-phosphatase system. FEBS Lett 1988; 229:179-82. [PMID: 2831086 DOI: 10.1016/0014-5793(88)80822-6] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The phosphate/pyrophosphate translocase protein (T2) of the hepatic microsomal glucose-6-phosphatase system was identified and then purified using antibodies raised against the rat mitochondrial phosphate/hydroxyl ion antiport protein. The T2 protein was shown to be absent in the microsomes isolated from a patient previously diagnosed as having type lc glycogen storage disease.
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38
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The phosphohydrolase component of the hepatic microsomal glucose-6-phosphatase system is a 36.5-kilodalton polypeptide. J Biol Chem 1988; 263:2673-8. [PMID: 2830258] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
The phosphohydrolase component of the microsomal glucose-6-phosphatase system has been identified as a 36.5-kDa polypeptide by 32P-labeling of the phosphoryl-enzyme intermediate formed during steady-state hydrolysis. A 36.5-kDa polypeptide was labeled when disrupted rat hepatic microsomes were incubated with three different 32P-labeled substrates for the enzyme (glucose-6-P, mannose-6-P, and PPi) and the reaction terminated with trichloroacetic acid. Labeling of the phosphoryl-enzyme intermediate with [32P]glucose-6-P was blocked by several well-characterized competitive inhibitors of glucose-6-phosphatase activity (e.g. Al(F)-4 and Pi) and by thermal inactivation, and labeling was not seen following incubations with 32Pi and [U-14C]glucose-6-P. In agreement with steady-state dictates, the amount of [32P]phosphoryl intermediate was directly and quantitatively proportional to the steady-state glucose-6-phosphatase activity measured under a variety of conditions in both intact and disrupted hepatic microsomes. The labeled 36.5-kDa polypeptide was specifically immunostained by antiserum raised in sheep against the partially purified rat hepatic enzyme, and the antiserum quantitatively immunoprecipitated glucose-6-phosphatase activity from cholate-solubilized rat hepatic microsomes. [32P]Glucose-6-P also labeled a similar-sized polypeptide in hepatic microsomes from sheep, rabbit, guinea pig, and mouse and rat renal microsomes. The glucose-6-phosphatase enzyme appears to be a minor protein of the hepatic endoplasmic reticulum, comprising about 0.1% of the total microsomal membrane proteins. The centrifugation of sodium dodecyl sulfate-solubilized membrane proteins was found to be a crucial step in the resolution of radiolabeled microsomal proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis.
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The phosphohydrolase component of the hepatic microsomal glucose-6-phosphatase system is a 36.5-kilodalton polypeptide. J Biol Chem 1988. [DOI: 10.1016/s0021-9258(18)69120-3] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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