ENZYME KINETICS 



stants for reactions involving ions may be very dependent upon 

 the nature and concentration of salt, and the rate constants of 

 reactions involving nonelectrolytes are not free from this effect. 

 Unfortunately the ideal buffer does not exist, and so it is neces- 

 sary to consider specific effects due to the components of the 

 buffer. In order to avoid large alterations in ionic strength, and 

 presumably in the individual rate constants, when the substrate 

 concentration is changed, the buffer concentration is generally 

 maintained at a value considerably higher than the highest 

 substrate concentration. 



There are a number of different ways in which electrolytes 

 can affect enzymatic catalysis. The binding of buffer ions by 

 the enzyme may give rise to any of the inhibiting or activating 

 effects discussed in the preceding section. The inclusion of such 

 equilibria in the mechanism alters further the interpretation of 

 the kinetic constants (1). 



In addition electrolytes will be expected to exert the same 

 types of effects which are encountered in studies of the kinetics 

 of nonenzymatic reactions. Two types of salt effects were dis- 

 cussed by Brbnsted, whose work forms the foundations of this 

 field of physical chemistry. When the concentration of electro- 

 lyte is changed, the activity coeflficients of the reactants and of 

 the activated complex are altered. Depending upon the signs 

 of the charges on the ions involved in the reaction this effect may 

 result in either a speeding up or slowing down of the reaction. 

 An additional effect of changing the concentration of electrolyte 

 on reactions catalyzed by weak acids or bases is to change the 

 degree of ionization of the catalyst. A similar effect is to be ex- 

 pected in enzymatic reactions if a particular ionized form of the 

 enzyme is a much better catalyst than the other ionized forms. 

 In the case of enzymatic reactions where several of these effects 

 may be of importance, the first problem is to separate them so 

 that the principles discovered in the study of simpler reactions 

 may be applied. 



The effect of electrolytes on the activity of urease has been 

 investigated intensively by Kistiakowsky and co-workers (10). 



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