Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.3.9 (glucose-6-phosphatase)
 3,081 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The role of phospholipids in the glucose-6-phosphatase system, including glucose-6-P phosphohydrolase and glucose-6-P translocase, was studied in rat liver microsomes by using phospholipases C and detergents. In the time course experiments on detergent exposure, the maximal activation of glucose-6-P phosphohydrolase varied according to the nature of the detergent used. On treatment of microsomes with phospholipase C of C. perfringens, the activity of glucose-6-P phosphohydrolase without detergent (i.e. without rupture of translocase activity) was gradually decreased with the progressive hydrolysis of phosphatidylcholine and phosphatidylethanolamine on the microsomal membrane, and was restored by incubation of these microsomes with egg yolk phospholipids. The extent of decrease in this phosphohydrolase activity in the detergent-exposed microsomes (with rupture of translocase activity) also varied depending on the detergent used (Triton X-114 or taurocholate). When 66% of the phosphatidylinositol on the membrane was hydrolyzed by phosphatidylinositol-specific phospholipase C of B. thuringiensis, the inhibition of glucose-6-P phosphohydrolase activity without detergent was very small. Although the inhibition of enzyme activity with detergent was apparently greater than that without detergent, the enzyme activity was stimulated by the breakdown of phosphatidylinositol when the enzyme activity was measured at lower concentration (0.5 mM) of substrate, glucose-6-P. The latency of mannose-6-P phosphohydrolase, a plausible index of microsomal integrity, remained above 70% after the hydrolysis of phosphatidylcholine, phosphatidylethanolamine, or phosphatidylinositol. The results show that the glucose-6-phosphatase system requires microsomal phospholipids for its integrity, suggesting that there exists a close relation between phosphatidylinositol and glucose-6-P translocase.
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PMID:Studies on the interactions between phospholipids and membrane-bound enzymes in microsomes. Effects of phospholipases C on the glucose-6-phosphatase system of rat liver microsomes. 630 98

Through kinetic analysis, the relationships between the glucose-6-phosphatase system and constituent phospholipids were studied in rat liver microsomes. When phosphoglycerides such as phosphatidylcholine and phosphatidylethanolamine on the microsomal membrane were hydrolyzed by phospholipase C of C. perfringens, the activities of glucose-6-P phosphohydrolase and glucose-6-P:glucose phosphotransferase both decreased with or without subsequent exposure to taurocholate. In these cases, the Michaelis constants (Km) for glucose-6-P were increased, concomitant with the decrease in the maximal velocities (Vmax) for glucose-6-P hydrolysis. On exposure to taurocholate, the apparent Km for glucose of phosphotransferase was decreased. When phosphatidylinositol was hydrolyzed by phosphatidylinositol-specific phospholipase C of B. thuringiensis, the activities of phosphohydrolase and phosphotransferase were both decreased on exposure to taurocholate. In this case, the value of Vmax of phosphohydrolase was decreased and that of Km for glucose-6-P was slightly decreased, while the apparent Km for glucose of phosphotransferase was increased. Without exposure to detergent, the activities of phosphohydrolase and phosphotransferase both decreased at glucose-6-P concentrations higher than 10 mM. However, at a concentration lower than 1 mM, the activity of phosphohydrolase became higher than that of the control, and Vmax and Km for glucose-6-P were decreased. A similar tendency was also observed in microsomes where membranous phosphatidylinositol was hydrolyzed, when they were treated with DIDS (an anion-transport inhibitor). From these results, it is concluded that the activity of glucose-6-phosphatase is greatly influenced by changes of the phospholipids on the microsomal membrane, and the activity of glucose-6-P translocase is stimulated by the breakdown of phosphatidylinositol.
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PMID:Studies on the interactions between phospholipids and membrane-bound enzymes in microsomes. Effects of phospholipases C on kinetic properties of the glucose-6-phosphatase system in rat liver microsomes. 630 99

Two mutations, R69D and K115E, converted a bacterial phosphatidylinositol-specific phospholipase C (PI-PLC) to a phosphatase with much higher specific activity toward glucose-6-phosphate than inositol-1-phosphate. PI-PLC single mutations R69D and K115E can cleave PI but lack any demonstrable phosphatase activity. The bacterial PI-PLC has no sequence homology with known glucose-6-phosphatase enzymes, which need His, Arg, and negatively charged residues (Asp or Glu) at the active site. The change in chemical reaction and substrate specificity can be rationalized by energy minimization of the mutant with I-1-P or G-6-P bound.
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PMID:Mutation of two active-site residues converts a phosphatidylinositol-specific phospholipase C to a glucose phosphatase. 1474 54