Hepatic Glucokinase in the Fed, Fasted, and Alloxan-Diabetic Rat

Abstract

Although impairmentof glucose utilization by the liver is a characteristic feature of the alloxan-diabetic rat (l-3), the metabolic site of this block is not certain.Tracer studies with C14labeled glucose, carried out in liver slices, suggest that glucose phosphorylation is the affected step (1, 3); however, there is a dearth of information concerning the enzyme system responsible for glucose phosphorylation in liver (4-6).Direct assays of liver glucokinase have been hampered principally by the presence of a powerful glucose 6-phosphatase.Crane and Sols (7) reported that this interfering enzyme can be removed with the microsomes by centrifugation at 100,000 x g after homogenization, and stated that the extract so obtained phosphorylates glucose at the rate of 0.4 to 0.6 pmole per g tissue.However, they gave no further details concerning the method of assay or the properties of this enzyme.With this observation as a point of departure, we undertook direct assays of this soluble glucokinase in rat liver in fed, fasting, and diabetic rats, and our results are described in this preliminary report.