SELF-KEGULATORY OR FEEDBACK SYSTEMS 



371 



in Fig. 7-36. Furthermore, the same effect on over-all rate is produced by 

 inhibition on either enzyme. A simple monolinear chain without feedback 

 would behave quite differently; there would be buffer capacity upon 

 inhibition of 'E^ and generally quite marked buffer capacity upon inhibition 

 of Eo. Reaction 1 is no longer the sole determinant of the rate. The results 



(^t 



Fig. 7-36. Effect of noncompetitive inhibition of Eg on the over-all 

 inhibition of a feedback system (Eq. 7-53) and on the concentration of 

 the inhibiting product. Same system as in Fig. 7-35. Curve 1: inhibition 

 of over-all rate. Curve 2: inhibition of Eo. Curve 3: concentration of C. 



may be understood to arise in the following ways. When Ej is inhibited by 

 an added inhibitor, the rate of formation of C is reduced so that (C) falls, 

 which releases Ej from some of the inhibition previously exerted on it by C. 

 Thus the over-all rate will not be inhibited proportionately to the inhibition 

 on E]^. Likewise, when E3 is inhibited there is a rise in (C) which will slow 

 down reaction 1 through the feedback inhibition, but (C) cannot rise to 

 a sufficient level to maintain the initial rate because its rate of formation 

 is reduced. A feedback system thus has less buffer capacity than a mono- 

 linear chain without feedback when an enzyme after the first is inhibited, 

 but greater buffer capacity when the initial enzyme in the chain is inhibited. 



