358 



7. INHIBITION IN MULTIENZYME SYSTEMS 



Effects of the Concentrations of Reactants and Regenerant 



In an irreversible monolinear chain, the steady-state rate is always 

 determined by the first reaction, but the coupling between the reactions 

 in a regenerative system gives the second reaction some importance also. 

 The steady-state rate is plotted as a function of the substrate AX in Fig. 7-30 

 (curve 2) where it may be compared to the rate in the absence of the second 

 reaction (curve 1). The depression caused by the second reaction is due 



Fig. 7-24. Noncompetitive inhibition of Ej in the cycHc system shown 

 in Fig. 7-16. (M)< = 10 mM. 



to the reduction in (B) that occurs in the steady state, part of it now being 

 in the form BX. Reaction 2 thus plays a role in the control of the rate by 

 its effect on the concentration of regenerant accepting the group X in 

 reaction 1. On the other hand, if there is a limited amount of regenerant, 

 the restoration carried out by reaction 2 allows the reaction to proceed 

 for a longer time than if no regeneration occurred. 



The changes in the ratio (BX)/(B), brought about by changes in the con- 

 centrations of substrate (AX), total regenerant (B),, and final acceptor 

 (C), are shown in Fig. 7-31. As expected, the ratio increases with rise in 



