180 



I. B. WILSON 



Fig. 3 



there is some sort of a weak covalent bond formed between the carbonyl car- 

 bon atom and some basic group in the protein. 



There is specificity associated with the acid portion of the substrate, but I 

 will not go into that (Augustinsson and Nachmansohn, 1949). 



The pH velocity curve of this enzyme (Fig. 3) is what one usually finds 

 (Wilson and Bergmann, 1950b). We assume there is an active form which we 

 represent as EH, an inactive E~ form in alkaline, and an inactive EH2"'" form 

 in acid. These last members either do not form the complex with the enzyme 

 or, if they do form the complex with the enzyme, the complex is not active. 



Actually we know that EHo"^ does not form the complex. E~ forms the 

 complex but the complex is inactive. 



We have interpreted the pH dependence then in terms of an acidic and basic 

 group, both of which are necessary for activity. We could assume (if we were 

 bold enough) that this basic group is the one that forms the covalent bond with 

 the carbonyl carbon atom of substrates, and we have gone on that basis and 

 have written our esteratic site, as shown in Fig. 4. We thus recognize two sub- 

 sites, an anionic site which reacts with the cationic head by ionic and van der 

 Waal's forces, and an esteratic site which combines with the ester part of the 

 substrate by a weak covalent bond between its basic group and the carbonyl 

 carbon atom. We have used the symbol GH where H represents the necessary 

 acid group and the pair of electrons represent the necessary basic group. G 

 may be a number of atoms. We do not specify its chemical identity. This is our 

 picture of the ES complex. 



The hydrolytic process which we propose (Wilson, Bergmann and Nach- 



