Presence, induction and possible role of glucose 6-phosphatase in mammalian pancreatic islets.
1. Pancreatic islets from several mammalian species were investigated for hydrolytic activity towards glucose 6-phosphate. Both the total phosphatase activity towards this substrate and the proportion cleaving glucose 6-phosphate in preference to beta-glycerophosphate varied widely between species. In pancreatic-islet homogenates prepared from mice and guinea pigs there was a higher rate of liberation of P(i) at pH6.7 from glucose 6-phosphate than from beta-glycerophosphate. In these two species cortisone treatment enhanced the enzyme activity towards glucose 6-phosphate but not that towards beta-glycerophosphate. Simultaneous injections of ethionine or puromycin blocked this stimulating effect of cortisone. 2. With whole homogenates of mouse pancreatic islets, inverse plots of the relationship between glucose 6-phosphate concentration and enzyme activity suggested the simultaneous action of two enzymes with different K(m) values. After fractionation of islets from obese-hyperglycaemic mice by differential centrifugation, one of these enzymes could be shown to be localized in the microsome fraction. It had K(m) for glucose 6-phosphate about 0.5mm and optimum pH6.7. It split glucose 6-phosphate in preference to beta-glycerophosphate, glucose 1-phosphate, fructose 6-phosphate and fructose 1,6-diphosphate. Incubation of the microsomes at pH5.0 and 37 degrees for 15min. decreased the enzyme activity by about 80%. Glucose was a potent inhibitor, the type of inhibition being neither strictly competitive nor non-competitive. It is suggested that the results indicate the presence of glucose 6-phosphatase in mammalian endocrine pancreas, and that this enzyme may play a role in the metabolic regulation of release of insulin.
D000818:Animals; D002498:Centrifugation; D003348:Cortisone / Q000037:antagonists & inhibitors / Q000494:pharmacology; D006224:Cricetinae; D004790:Enzyme Induction; D005001:Ethionine / Q000494:pharmacology; D005260:Female; D005947:Glucose / Q000494:pharmacology; D005952:Glucose-6-Phosphatase / Q000032:analysis / Q000378:metabolism*; D005994:Glycerophosphates / Q000378:metabolism; D006168:Guinea Pigs; D006863:Hydrogen-Ion Concentration; D006943:Hyperglycemia / Q000378:metabolism; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000201:enzymology*; D007700:Kinetics; D008297:Male; D051379:Mice; D008861:Microsomes / Q000378:metabolism; D009765:Obesity / Q000378:metabolism; D011691:Puromycin / Q000494:pharmacology; D013045:Species Specificity
D005994:Glycerophosphates; D007328:Insulin; D011691:Puromycin; D005952:Glucose-6-Phosphatase; D005947:Glucose; D003348:Cortisone; D005001:Ethionine