548 



12. RATES OF INHIBITION 



after 10 min and a slower one that was incomplete after 2 h. One might 

 postulate that the rapid reaction involves the oxidation of sulf hydryl groups 

 near, but not at, the active site, and that the slow reaction represents a 

 progressive inactivation or denaturation of the enzyme due to the struc- 

 tural alteration resulting from the formation of — S — S— bonds. Such 

 secondary inactivation of enzymes will be discussed in a subsequent section. 



TIME 



MIN 



Fig. 12-10. Inhibition of monoamine oxidase by iproniazid 



plotted logarithmically. (From Davison, 1957). Curve A: (I) = 



1.65 mi/; curve B, (I) = 5 mM; curve C, (I) = 25 mM. 



Mutual Depletion Systems 



When the concentrations of both enzyme and inhibitor are reduced during 

 the reaction between them, not only the final inhibition but also the rate 

 at rt^hich this is attained is altered compared to the situation in which 

 the inhibitor is markedly in excess of the enzyme. The initial rate of inhi- 



