ANOMERIC SPECIFICITY OF THE NATIVE AND MUTANT FORMS OF HUMAN BETA-CELL GLUCOKINASE

The anomeric specificity of wild-type human beta-cell glucokinase and six of its mutant forms toward alpha- and beta-D-glucose was examined over 6-min incubation at 30 degrees C, When D-[U-C-14]glucose at anome ric equilibrium was used as substrate, the wild-type form yielded a ma ximal velocity of 76 U/mg, a K-m of 4-5 mM, and a Hill coefficient clo se to 1.2, The maximal velocity (2 to 89 U/mg) and K-m (2.4 to 209.8 m M) of the mutant forms both covered a range of about two orders to mag nitude, Wild-type glucokinase displayed a higher affinity for alpha-D- glucose but greater maximal velocity with beta-D-glucose, At variance, however, in four mutant forms, the maximal velocity was higher with a lpha- than beta-D-glucose, These findings indicate that the higher ins ulinotropic efficiency of alpha- than beta-glucose cannot be ascribed to the intrinsic catalytic properties of human beta-cell glucokinase, They also suggest that the perturbation of the anomeric specificity of glucose-stimulated insulin release in type-a diabetes could conceivab ly be attributable, on occasion and at least in part, to a mutation of the glucokinase gene. (C) 1996 Academic Press, Inc.