51
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Claeyssens S, Chedeville A, Lavoinne A. Inhibition of protein phosphatases activates glucose-6-phosphatase in isolated rat hepatocytes. FEBS Lett 1993; 315:7-10. [PMID: 8380144 DOI: 10.1016/0014-5793(93)81121-f] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Incubation of hepatocytes in the presence of microcystin-LR, okadaic acid, calyculin A (inhibitors of protein phosphatases PP1 and PP2A) or microcystin-RR (a specific inhibitor of PP2A) activated glucose-6-phosphatase both in the supernatant and in intact or disrupted microsomes. Puromycin, an inhibitor of protein synthesis, totally suppressed this activating effect, suggesting the involvement of protein phosphatases in the regulation of glucose-6-phosphatase synthesis.
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Affiliation(s)
- S Claeyssens
- Groupe de Biochimie et Physiopathologie digestive et Nutritionnelle, UFR Médecine-Pharmacie, Saint-Etienne du Rouvray, France
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52
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Waddell ID, Burchell A. 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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Affiliation(s)
- I D Waddell
- Department of Child Health, University of Dundee Medical School, Ninewells Hospital, Scotland, UK
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53
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Goldberg JD, Treleaven SC, Koresawa M, Simpson T, Golbus MS. Unreliability of platelet glucose-6-phosphatase for the diagnosis of glycogen storage disease type Ia. J Inherit Metab Dis 1993; 16:844-50. [PMID: 8295399 DOI: 10.1007/bf00714276] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The diagnosis of glycogen storage disease type Ia currently uses enzyme analysis of liver tissue. This requires liver biopsy in the at-risk neonate or fetus. Conflicting reports have appeared in the literature on the use of peripheral platelet glucose-6-phosphatase activity for the diagnosis of this disorder. We have applied a sensitive radiometric assay system to the measurement of glucose-6-phosphatase activity in peripheral platelets. Two families with affected members were analysed, revealing no differences in glucose-6-phosphatase activity as compared with control values. Platelet measurement of glucose-6-phosphatase does not appear to be useful for the diagnosis of glycogen storage disease type Ia.
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Affiliation(s)
- J D Goldberg
- Department of Obstetrics, Gynecology and Reproductive Sciences, University of California, San Francisco 94143
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54
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Burchell A, Waddell ID. 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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Affiliation(s)
- A Burchell
- Department of Obstetrics and Gynaecology, University of Dundee Medical School, Ninewells Hospital, Scotland, UK
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55
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Rush JS, Waechter CJ. An anion-exchange radioassay for glucose 6-phosphate phosphatase: use in topological studies with endoplasmic reticulum vesicles. Anal Biochem 1992; 206:328-33. [PMID: 1332548 DOI: 10.1016/0003-2697(92)90374-g] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
A simple procedure is presented for the enzymatic preparation of [2-3H]mannose 6-phosphate (Man 6-P) with purified yeast hexokinase and unlabeled ATP. The enzymatically synthesized [2-3H]Man 6-P is utilized as the radiolabeled substrate in a new rapid assay for glucose 6-phosphate (Glc 6-P) phosphatase. The principle of the assay procedure is that the unreacted substrate, [2-3H]Man 6-P, is retained by the anion-exchange resin, AG 1-X8 (acetate), while the enzymatic product, [2-3H]-mannose, is eluted directly into a scintillation counting vial. When Glc 6-P phosphatase activity associated with mouse liver endoplasmic reticulum (ER) vesicles is assayed by the new chromatographic assay, the same characteristic latency and properties are observed, as determined by the commonly used colorimetric assay of inorganic phosphate produced. The anion-exchange radioassay described should be useful for a variety of topological studies on enzymes associated with membrane vesicles derived from liver and kidney ER.
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Affiliation(s)
- J S Rush
- Department of Biochemistry, University of Kentucky College of Medicine, A. B. Chandler Medical Center, Lexington 40536
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56
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Fulceri R, Bellomo G, Gamberucci A, Scott HM, Burchell A, Benedetti A. Permeability of rat liver microsomal membrane to glucose 6-phosphate. Biochem J 1992; 286 ( Pt 3):813-7. [PMID: 1417741 PMCID: PMC1132976 DOI: 10.1042/bj2860813] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Light-scattering measurements of osmotically induced changes in the size of rat liver microsomal vesicles pre-equilibrated in a low-osmolality buffer revealed the following. (1) The increase in extravesicular osmolality by addition of glucose 6-phosphate or mannose 6-phosphate (25 mM each) caused a rapid shrinking of microsomal vesicles. After shrinkage, a rapid swelling phase (t1/2 approx. 22 s) was present with glucose 6-phosphate but absent with mannose 6-phosphate, indicating that the former had entered microsomal vesicles, but the latter had not. (2) Almost identical results were obtained in the absence of any glucose 6-phosphate hydrolysis, i.e. with microsomes pre-treated with 100 microM-vanadate. (3) The anion-channel blocker 4,4'-di-isothiocyanostilbene-2,2'-disulphonic acid (DIDS) suppressed the glucose 6-phosphate-induced swelling phase. (4) The swelling phase was more prolonged as the glucose 6-phosphate concentration increased (t1/2 = 16 +/- 3, 22 +/- 3 and 35 +/- 4 s with 25 mM, 37.5 mM- and 50 mM-glucose 6-phosphate respectively). The behaviour of glucose-6-phosphatase activity of intact and disrupted microsomes measured in the presence of high concentrations (less than 30 mM) of substrate also indicated the saturation of the glucose 6-phosphate permeation system by extravesicular concentrations of glucose 6-phosphate higher than 20-30 mM. Additional experiments showed that vanadate-treated microsomes pre-equilibrated with 0.1 mM- and 1.0 mM-glucose 6-phosphate (and [1-14C]glucose 6-phosphate as a tracer) rapidly (t1/2 less than 20 s) released [1-14C]glucose 6-phosphate when diluted in a glucose 6-phosphate-free medium. The efflux of [1-14C]glucose 6-phosphate was largely prevented by DIDS, allowing an evaluation of the intravesicular space of glucose 6-phosphate of approx. 1.0 microliter/mg of microsomal protein.
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Affiliation(s)
- R Fulceri
- Istituto di Patologia Generale, University of Siena, Italy
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57
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Waddell ID, Zomerschoe AG, Voice MW, Burchell A. 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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Affiliation(s)
- I D Waddell
- Department of Child Health, Ninewells Hospital and Medical School, Dundee, Scotland, U.K
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58
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Hume R, Lyall H, Giles M, Burchell A. Impairment of the activity of the hepatic microsomal glucose-6-phosphatase system in three preterm infants. Acta Paediatr 1992; 81:580-4. [PMID: 1327322 DOI: 10.1111/j.1651-2227.1992.tb12304.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Three preterm infants born at 26-30 weeks' gestation who died between 103 and 266 days after birth were found to have elevated hepatic glycogen levels. Kinetic analysis of the hepatic microsomal glucose-6-phosphatase system demonstrated that one infant had abnormally low levels of activity of the glucose-6-phosphatase enzyme (partial type 1a glycogen storage disease) and two had deficiencies of T2, a microsomal phosphate/pyrophosphate transport protein (type 1c glycogen storage disease). In all three cases glycogen storage disease was not suspected prior to death even though both hypo- and hyperglycaemic episodes were recorded in the first 15 days after birth indicating that they had somewhat disordered blood glucose regulation. In the infant with low glucose-6-phosphatase enzyme activity, abnormal development of the glucose-6-phosphatase enzyme cannot be ruled out. This is the first description of abnormalities in the glucose-6-phosphatase system in preterm infants.
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Affiliation(s)
- R Hume
- Department of Obstetrics and Gynaecology, Ninewells Hospital and Medical School, University of Dundee, Scotland
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59
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Abstract
Microsomal glucose-6-phosphatase catalyses the last step in liver glucose production. Glucose-6-phosphatase deficiency, now termed type 1 glycogen storage disease, was first described almost 40 years ago but until recently very little was known about the molecular basis of the various type 1 glycogen storage diseases. Recently we have shown that at least six different proteins are needed for normal glucose-6-phosphatase activity in liver. Four of the proteins have been purified and three cloned. Study of the type 1 glycogen storage diseases has stimulated investigations of the mechanisms of small molecule transport across the endoplasmic reticulum membrane and demonstrated the existence of novel endoplasmic reticulum transport proteins for glucose and phosphate.
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Affiliation(s)
- A Burchell
- Department of Obstetrics and Gynaecology, University of Dundee, Ninewells Hospital and Medical School, Scotland, UK
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60
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Nordlie RC, Scott HM, Waddell ID, Hume R, Burchell A. 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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Affiliation(s)
- R C Nordlie
- Department of Biochemistry and Molecular Biology, School of Medicine, University of North Dakota, Grand Forks 58202
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61
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Grant A, Macgregor AM, Burchell A. Characterization of glucose-6-phosphatase in hepatocytes. Effects of amiloride and pentamidine. Biochem Pharmacol 1991; 42 Suppl:S27-32. [PMID: 1662952 DOI: 10.1016/0006-2952(91)90388-l] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The hepatic microsomal glucose-6-phosphatase enzyme is situated inside the lumen of the endoplasmic reticulum and, for normal enzyme activity in vivo, three transport systems are needed for the substrate glucose-6-phosphate and the products phosphate and glucose. Previous studies using isolated microsomes showed that the drugs amiloride and pentamidine do not affect the glucose-6-phosphatase enzyme but can activate the glucose-6-phosphate transport system. Here we demonstrate that, very surprisingly, the addition of pentamidine (and to a lesser extent amiloride) to isolated hepatocytes results in an inhibition of the catalytic subunit of glucose-6-phosphatase.
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Affiliation(s)
- A Grant
- Department of Obstetrics and Gynaecology, Ninewells Hospital and Medical School, University of Dundee, U.K
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62
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Foster JD, Nelson KL, Sukalski KA, Lucius RW, Nordlie RC. Hysteretic behavior of the hepatic microsomal glucose-6-phosphatase system. BIOCHIMICA ET BIOPHYSICA ACTA 1991; 1118:91-8. [PMID: 1662542 DOI: 10.1016/0167-4838(91)90445-6] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Carbamyl-P:glucose and PPi:glucose phosphotransferase, but not inorganic pyrophosphatase, activities of the hepatic microsomal glucose-6-phosphatase system demonstrate a time-dependent lag in product production with 1 mM phosphate substrate. Glucose-6-P phosphohydrolase shows a similar behavior with [glucose-6-P] less than or equal to 0.10 mM, but inorganic pyrophosphatase activity does not even at the 0.05 or 0.02 mM level. The hysteretic behavior is abolished when the structural integrity of the microsomes is destroyed by detergent treatment. Calculations indicate that an intramicrosomal glucose-6-P concentration of between 20 and 40 microM must be achieved, whether in response to exogenously added glucose-6-P or via intramicrosomal synthesis by carbamyl-P:glucose or PPi:glucose phosphotransferase activity, before the maximally active form of the enzyme system is achieved. It is suggested that translocase T1, the transport component of the glucose-6-phosphatase system specific for glucose-6-P, is the target for activation by these critical intramicrosomal concentrations of glucose-6-P.
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Affiliation(s)
- J D Foster
- Department of Biochemistry and Molecular Biology, University of North Dakota School of Medicine, Grand Forks 58202
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