17:4/ Enzyme Kinetics of Hydrolytic Reactions 



331 



This equation indicates that the maximum velocity obtainable will be 

 less than V m&x even if only a trace of the inhibitor x' is present; it is 

 illustrated in Figure 10b. Other types of inhibitors have been found 

 and studied. For instance, some may react with ES but not with E. 



1,500 



Phenyl Propionate 



A 



Phenyl Acetate 



Phenyl 



Bui y rate 



Uninhibited 



6- 





100 



20 



40 



»'A 



(a) 



N 2 

 (b) 



Figure 10. (a) Competitive inhibition of the hydrolysis of 

 carboxybenzoxyglycyl-DL-phenylalanine by carboxypeptidase. 

 The inhibitor concentrations were all 2 x 10 ~ 3 M. (b) Non- 

 competitive inhibition by CO of N 2 fixation in Azotabacter. 

 The data could also be interpreted as indicating this reaction 

 does not obey simple Michaelis-Menten kinetics. After F. M. 

 Huennekens, "Biological Reactions: Measurement and General 

 Theory," Technique of Organic Chemistry, Vol. 8, Investigations 

 of Rates and Mechanisms of Reactions, S. L. Friess and A. 

 Weissberger, eds. (New York: Interscience Publishers Inc., 

 1953). 



Many other variations are possible, but it does not seem fruitful to 

 pursue their discussion here. 



Inhibitors have been, and are, used widely to study enzymes and 

 investigate enzymatic pathways. In several cases, as in helping unravel 

 the pathways of the utilization of glucose, inhibitors have proved helpful 

 in blocking the process at desired points. In other cases, the inhibitors 

 have been misleading because they have had more than one action. In 

 a few cases, it has been possible to find certain details of the active 

 surface of the enzyme by observing inhibitor action. 



References on Enzymes are included at the end of Chapter 18. 



