Glucokinase in bird liver: a membrane bound enzyme

There have been numerous reports that liver of birds contain only isoenzymes of the low K_M hexokinases, but lack the high K_M glucokinase. We describe here the presence of glucokinase in livers of chicken and Japanese quail. The enzyme is membrane bound and is solubilized by vigorous mechanical disruption of the tissue. With gentle homogenization the glucokinase is recovered upon centrifugation in the 1000g pellet, from which it may be liberated by prolonged sonication. It appears to be localized in the cell plasma membrane. The activities of hexokinase and glucokinase appear to be about equal in liver parenchyma of fed chicken, but in that of Japanese quail the activity of glucokinase exceeds greatly that of hexokinase.