Kinetic behaviour of liver glucokinase in diabetes. II. Possible role of non-enzymatic protein glycation.

The phosphorylation of D-glucose, as catalyzed by liver postmicrosomal supernatants, prepared from diabetic rats, under conditions aiming at the characterization of gluco-kinase activity, indicates, in addition to the classical fall in enzyme activity, an altered kinetic behaviour, the affinity for D-glucose and the apparent energy of activation being both lower in diabetic than normal rats. These kinetic anomalies persist after separation of cytosolic proteins from low molecular weight metabolites by gel filtration chromatography. They are simulated, to a limited extent, when liver cytosolic proteins from normal rats are glycated in vitro through prolonged exposure to a high concentration of D-glucose. Diabetes causes an increased non-enzymatic glycation of liver cytosolic proteins, including lactate dehydrogenase, as judged by either the ketoamine test, a back-titration procedure or the separation of glycated proteins by affinity chromatography. These findings suggest that chronic hyperglycemia might alter the intrinsic properties of liver glucokinase through a process of non-enzymatic glycation.