Anomeric specificity of hexokinase and glucokinase activities in liver and insulin-producing cells.

Conflicting data have been reported concerning the anomeric specificity of glucokinase. In the present study, liver hexokinase (Km for D-glucose 0.4 mM) displayed a higher affinity for but lower Vmax. with alpha- than with beta-D-glucose. The velocity of the reaction catalysed by liver glucokinase was higher with with beta- than with alpha-D-glucose, whatever the glucose concentration. The apparent Km of glucokinase was somewhat lower, however, with alpha- than with beta-D-glucose. Comparable results were obtained for the high-Km glucokinase-like enzymic activity present in normal pancreatic islets or insulin-producing tumoral cells. These results suggest that the anomeric specificity of glucokinase cannot account for the higher rate of glycolysis found in islets exposed to alpha- as distinct from beta-D-glucose.