Glucokinase of Rabbit Liver PURIFICATION AND PROPERTIES* Josti SALAS,~ MARGARITA SALAS,$ ELADIO VIRUELA,J AND ALBERTO SOLS

It has been recently shown that in rat liver there are two enzymes which phosphorylate glucose to glucose 6-phosphate. One of them is a hexokinase with a great affinity for glucose and, like those of other animal tissues it is inhibited by glucose 6phosphate; the other one, named glucokinase, has a low affinity for glucose, is not inhibited by glucose 6phosphate, and appears to be responsible for glycogen synthesis from glucose in liver (1). Hexokinase activity exists in both fetal and adult liver whereas glucokinase develops after birth (2). Results from several laboratories have shown that glucokinase activity disappears as a result of fasting and diabet,es and reappears after refeeding or insulin administration, respectively (l-9), and that this reappearance involves synthesis de nouo of the enzyme apparently mediated by insulin (3, 4, 6, 10). This paper describes the purification of rabbit liver glucokinase about 200-fold and some properties of the enzyme. Rabbit liver glucokinase is activated by sulfhydryl reagents and is protected by potassium ions. Besides glucose, mannose and 2-deoxyglucose are good substrates of the glucokinase. Glucosamine and several N-substituted derivatives are strong competitive inhibitors of the glucokinase. Adenosine diphosphate inhibits the enzyme; this inhibition is only partially reversed by adenosine triphosphate.