FRANK M. HUENNEKENS 



mal energy have a much greater probability of completing the 

 reaction. A catalyst produces these favorable distortions by 

 binding the substrate in a strained configuration, and, to be sure, 

 this temporary debt of the binding energy must be repaid out of 

 the net proceeds gained from the reaction. 



It follows from the above discussion that in enzymatic re- 

 actions we must direct our attention to the binding of substrates 

 by the protein catalysts. Many enzymatic reactions may be 

 divided into three categories. 



a. The components of one substrate are used to cleave a 

 bond in the second substrate : 



H2O + A - B > AH + BOH (15) 



b. Two substrates form a new bond by the loss of a group 

 from each ; where H2O is removed the reaction is the reverse of 

 equation (15). 



c. The transfer of a group from a donor substrate to a 

 similar acceptor substrate, e.g., equations (1) and (2). 



All of these categories involve two substrates* so that we may en- 

 vision a ternary complex where both reactants, or substrates, are 

 bound in close juxtaposition on the enzyme surface and the 

 necessary transfers take place in serial order. It may be argued 

 that a ternary complex is not necessary (and perhaps less likely 

 in a kinetic sense), so that two consecutive binary complexes are 



.H . 

 formed, i.e., in the case of {a) above, where E\ ^^ ^"^ enzyme: 



A - B + E< > AH + BOH + E (16) 



^OH 



followed by regeneration of the hydrated enzyme : 



E + H2O > E< (17) 



\OH 



* There is some evidence that even reactions involving internal re- 

 arrangements of a single substance, i.e., A ^ A', are bimolecular with respect 

 to A. 



508 



