The Nature and Diversity of Catalytic Proteins 79 



example conies from the kinases which catalyze transfer of the termi- 

 nal phosphoryl group of ATP to various acceptors. Studies in our 

 laboratory (see ref. 4) and that of Mildred Cohn (25) have shown 

 that in various kinase reactions, the catalvsis occurs with a cleavage of 

 the bond between the phosphorus atom of the group transferred and 

 the oxygen atom linking the phosphoryl group to the rest of the donor 

 molecule, and that the phosphoryl group is transferred without inter- 

 change of its oxygens with oxygens from water or substrates. Recently 

 we have probed further the details of the pyruvate kinase and hexo- 

 kinase reactions by study of the reaction kinetics and substrate binding 

 (261. These and earlier studies have led to a concept of the catalysis 

 as depicted in Fig. 2 for pyruvate kinase. The pattern given in this 



ATP 



ADP 



Phosphopyruvate 



Pyruvate 



A 



CH 2 

 II II II II 



Adenine- Ribose— P-0 — P- P 0— C-C00 



1 I /\ 

 0_ 0_ _0 0_ 



FIG. 2. A schematic illustration of substrate binding and a transition state for 

 pyruvate kinase. 



figure likely holds for other kinases as well. Simple but important 

 aspects are that ATP and ADP share a common binding site, and 

 pyruvate and phosphopyruvate another binding site, but that both 

 ATP and phosphoenolpyruvate cannot be bound to the enzyme at the 

 same time because of a common position at the active site for their 

 transferable phosphoryl group. 



An important feature of the catalysis by kinases, as indicated for 

 pyruvate kinase in Fig. 2, is the transfer of the phosphoryl group 

 directly from the donor to the acceptor, without formation of any 

 phosphoryl enzyme intermediate. This is in contrast to the intra- 

 molecular phosphoryl transfer catalyzed by phosphoglucomutase, in 

 which there is good evidence for a phosphoryl enzyme intermediate 

 (27). Also, speculation has become common that many enzyme re- 



