Space-filling models of kinase clefts and conformation changes.

Space-filling models of yeast hexokinase, adenylate kinase, and phosphoglycerate kinase drawn by computer clearly portray the bilobal character of these phosphoryl transfer enzymes, and the deep cleft which is formed between the lobes. A dramatic conformational change occurs in hexokinase as glucose binds to the bottom of the cleft, which causes the two lobes of hexokinase to come together. A substrate-induced closing of the active site cleft is postulated to occur in other kinases as well. This change may provide a mechanism by which some of these enzymes reduce their inherent adenosine triphosphatase activity and could be a general requirement of the kinase reaction.