title: Carbohydrate metabolism and the glucoreceptor mechanism.
abstract: Current views on the recognition of sugars as signals for insulin biosynthesis and release are discussed. Evidence is presented that the initial steps in the metabolism of N-acetyl-glucosamine differ from those in glucose metabolism in that for the former transport into the islet represents the rate-limiting step. Different enzymes phosphorylate these two sugar, but it is suggested that N-acetylglucosamine and glucose enter the beta-cell via the same carrier since 3-O-methylglucose is shown to be a competitive inhibitor of N-acetylglucosamine oxidation. Inhibitory effects on N-acetylglucosamine oxidation are also observed with caffeine, 3-isobutyl-methylxanthine and phloretin. Inhibition of N-acetylglucosamine metabolism is associated with inhibition of N-acetylglucosamine-stimulated insulin release and biosynthesis. Methylxanthines also inhibit uptake of 45Ca2+ by islet mitochondria. The possible physiological role of islet mitochondrial Ca2+ uptake in the regulation of beta-cell cytosolic Ca2+ concentration is discussed.
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000117:Acetylglucosamine / Q000378:metabolism*; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D005944:Glucosamine / Q000031:analogs & derivatives*; D005947:Glucose / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000378:metabolism; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000378:metabolism*
chemical_list: D007328:Insulin; D011956:Receptors, Cell Surface; C027786:glucose receptor; D002110:Caffeine; D000242:Cyclic AMP; D005947:Glucose; D005944:Glucosamine; D002118:Calcium; D015056:1-Methyl-3-isobutylxanthine; D000117:Acetylglucosamine