354 



7. INHIBITION IN MULTIENZYME SYSTEMS 



as given by dijdi i becomes less than unity and the cycle rate is sensitive 

 to inhibition (Fig. 7-21). 



(5) If the concentration of a particular cycle intermediate is important, 

 as in determining the rate of some side reaction, inhibition can often alter 

 this concentration markedly and produce changes in pathways outside 

 the cycle. For example, inhibition of certain steps in the tricarboxylic 

 acid cycle may influence amino acid metabolism through transaminations 

 involving the keto acid intermediates. 



Fig. 7-20. Noncompetitive inhibition of Ej in the cycHc system shown in Fig. 7-16. 



(M)( = 10 mif . 



(6) Competitive inhibition in a cyclic system will have effects which 

 differ little from noncompetitive inhibition, due to the fact that the sub- 

 strate for the enzyme inhibited cannot increase in concentration suffi- 

 ciently to antagonize the inhibition greatly. 



REGENERATIVE SYSTEMS 



An enzyme sequence catalyzing reactions in which one or more sub- 

 stances serve as acceptors and donors, alternately gaining and losing groups, 



