BRANCHED LINEAR CHAINS 343 



not saturated, inhibition of Eg will produce a rise in (B) which will in- 

 crease the rate of reaction 3. Since v^ + v^ must remain constant in the 

 steady state, an increase in v^ implies a decrease in ^2. This divergent 

 chain thus has less buffer capacity generally than the monolinear system. 

 The effects of inhibition of E^ are particularly interesting since the result- 

 ing rise in (B) may increase d{C)ldt and such a mechanism may be one 

 of the explanations for the stimulation frequently observed with enzyme 

 inhibitors. The variation in d{C)jdt is plotted against Fg in Fig. 7-14 and 

 from such a curve the degree of inhibition of d{G)jdt by reduction in Fg 

 through noncompetitive inhibition may be calculated. The amount of stimu- 

 lation will depend on the relative values of v^ and v^ in the uninhibited 

 system. For the particular system plotted, the stimulation of d{0)jdt for 

 different initial values of Fg at an inhibition of E.^ of 90% is as follows: 



Another type of divergent chain may occur when an intermediate spon- 

 taneously decomposes nonenzymically into a product other than the en- 

 zymically catalyzed one. 



El E, c 



The reaction of B ^ D may be assumed to be monomolecular and Vg = 

 k{B) rather than the value in Eq. 7-26 above. The essential difference 

 between this system and the three-enzyme system is that reaction 3 cannot 

 now become saturated and the rate will always be linear with (B), which 

 is given by: 



k[{A) + A^](B)=+ {(V,+ kK,)[{A) + AM - (A)F,}(B) - V,K,{A) = (7-28) 



Thus if E.2 is inhibited, (B) will rise slightly but never sufficiently to main- 

 tain the initial d{C)ldt.; if V^ is much smaller than kK.^, as seen from Eq. 7-28, 

 changes in F, will scarcely affect (B) and no buffer capacity will be observed. 

 It may also be noted that the system will always be in a steady state what- 

 ever the concentration of A. The spontaneous reactions of unstable inter- 

 mediates, such as free radicals, may be important in several metabolic 

 pathways. 



