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In the post-microsomal supernatant of pancreatic islets, prepared from fasted or fed rats, D-fructose 1-phosphate increased the activity of glucokinase by 20–30% as measured in the presence of D-glucose 6-phosphate and D-fructose 6-phosphate. Such an activation was less marked than that found in liver extracts. The islet cytosol was also found to inhibit purified liver glucokinase, and this effect was antagonized by D-fructose 1-phosphate. In the presence of hexose 6-phosphates, partially purified islet glucokinase was inhibited by the hepatic glucokinase regulatory protein in a D-fructose-1-phosphate-sensitive manner. In intact islets, D-glyceraldehyde stimulated the generation of 14C-labelled D-fructose 1-phosphate from D-[U-14C]glucose and increased the production of ³H2O from D-[5-³H]glucose. These findings suggest that the activity of glucokinase in islet cells may be regulated by a protein mediating the antagonistic effects of D-fructose 6-phosphate and D-fructose 1-phosphate in a manner qualitatively similar to that operating in hepatocytes, bat with lower efficiency. [ABSTRACT FROM AUTHOR]

Examines the anomeric specificity of D-glucose metabolism in rat adipocytes. Rate of D-glucose utilization; Presence of equilibrated D-glucose; Anomeric specificity of D-glucose metabolism in adipocytes; Fraction of D-glucose catabolism through the pentose cycle; Oxidation of glucose.

The membrane-accessible diacylglycerol 1-oleoyl-2-acetyl-sn-glycerol (OAG, 5-500 µM) caused a dose-related activation of protein kinase C in rat islet homogenates. In islet cell membranes exposed to [γ-323P]ATP, OAG (100 µM) stimulated the net production of labeled phosphatidate and inhibited that of labeled phosphatidylinositol 4-phosphate. In intact islets exposed to 5.6 mM D-glucose, OAG (100 µM) decreased the outflow of 56Rb, increased that of 45Ca and caused a rapid stimulation of insulin release. The secretory response to OAG was dose-related in the 50-500 µM range, being most marked, in relative terms, at a glucose concentration close to the threshold value for stimulation of insulin release by this hexose. It was decreased but not abolished in the absence of CaCl2 and presence of EGTA. At variances with tumor-promoting phorbol esters, OAG failed to potentiate insulin release stimulated by a hypoglycaemic sulphonylurea. Although these findings support the view that activation of protein kinase C by diacylglycerol represents an efficient modality for stimulation of insulin release, they suggest that the effect of OAG upon islet function may not be solely attributable to such an activation. [ABSTRACT FROM AUTHOR]