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Kinetics and specificity of human B-cell glucokinase: Relevance to hexose-induced insulin release

par Sener, Abdullah ;Malaisse, Willy
Référence Biochimica et biophysica acta. Molecular cell research, 1312, 1, page (73-78)
Publication Publié, 1996-06

Article révisé par les pairs

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Résumé :

The present study reevaluates the relevance of human B-cell glucokinase activity to the process of hexose-induced insulin release. Taking into account a phenomenon of positive cooperativity (Hill number: 1.34), the K(m) of the enzyme for glucose (≤5.1 mM) was lower than the concentration of the hexose required to cause half-maximal stimulation of insulin release in intact islets. Likewise, there were obvious discrepancies between the kinetics of glucose, mannose and fructose phosphorylation by B-cell glucokinase, e.g. in terms of maximal velocity, and the secretory and metabolic responses to these hexoses in intact islets. Glucose 6-phosphate decreased, modestly but significantly, B-cell glucokinase activity, such an inhibitory action being of the non-competitive type. Mannoheptulose caused competitive inhibition of B-cell glucokinase. It is concluded that the intrinsic catalytic properties of B-cell glucokinase cannot fully account for the concentration dependency and sugar specificity of the secretory response to D-glucose or other hexoses in pancreatic islets.