The role of glucokinase in the phosphorylation of glucose by rat liver

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Abstract
Determination of the activities of the two hepatic glucose-phosphorylatlng enzymes, glucoklnase and hexokinase, in the presence of one another is possible because of their very different apparent affinities for glucose. A method for their determination based on this is described. Glucokinase accounts for the major portion of the total glucose-phosphorylating activity in the fed rat. Normal values are given. Glucokinase activity is decreased by starvation but is unchanged during phlorrhizln-glucosuria. Alloxan-dlabetes is characterized by negligible or very low glucokinase activity. Insulin treatment of alloxan-diabetic rats restores this to normal levels. Hexokinase activity is unaffected during all such changes. Cortisone treatment results in lowered activities of both enzymes, and simultaneous treatment with insulin does not prevent this less-specific change. The results provide an enzymic basis for many previous observations on liver slices. Possible ways in which changes in the two enzymes may effect control of carbohydrate metabolism are discussed. It is suggested that insulin may control glucokinase synthesis in the liver.