Kinetic behaviour of liver glucokinase in insulinopenic situations: effect of fructose 1-phosphate in fed and starved rats

Abstract In the liver postmicrosomal supernatant of starved rats, the high- K m glucose-phosphorylating enzymic activity, presumably attributable to glucokinase, is not solely decreased but also displays an apparently lower affinity and less pronounced temperature dependency than in fed rats. In the presence of exogenous d -glucose 6-phosphate and d -fructose 6-phosphate, the rate of d -glucose phosphorylation is enhanced by d -fructose 1-phosphate at low (10 mM) but not high (90 mM) hexose concentration and at high (30–37°C) but not low (10°C) temperature. The responsiveness of glucokinase to d -fructose 1-phosphate is apparently decreased in starved animals. Nevertheless, the latter ester does not suppress the starvation-induced alteration in both the apparent affinity and temperature dependency of liver glucokinase. It is proposed, therefore, that such an alteration may reflect changes in the intrinsic properties of the high- K m hepatic enzyme.