386 



7. INHIBITION IN MULTIENZYME SYSTEMS 



that (B), — (B) is much greater when (A) is high; thus (B) must rise more 

 and reaction 2 is corresioondingly increased in rate. There is also an in- 

 crease in Atf^g when V^ is increased relative to Fg. 



Table 7-3 

 Variation of Transition Time with Substrate Concentration " 



" Xoncojnpetitive inhibition of Ej with i = 0.5. Constants as in Table 7-2. 



Finally, one may inquire into the change in transition time when both 

 Vi and V2 are increased or decreased equally, V^IV^ remaining constant It 

 may be shown that (B) and (B), remain the same, since they depend only 

 on F1/F2, and that if F^ and Fg are changed j:'-fold, J?/o.9 will be changed 

 by a factor of 1/x, inasmuch as the denominators in both terms of Eq. 

 7-72 will be multiplied by x. Hence, as expected, the more rapid the rates 

 of the enzymes composing a monolinear chain, the shorter will be the time 

 necessary to change from one steady state to another. 



Fluctuation and Overshoot 



In more complex multienzyme systems, the transition between steady 

 states may not follow the simple logarithmic course. When, following inhi- 

 bition, the rate falls to a level below the final steady state and then rises 

 to it, the time variation of the rate may not be as simple as previously 

 described. The rate may not drop suddenly as in Fig. 7-39. In the three- 

 step monolinear chain, A -> B ^ C -^ D, inhibition of Ej will usually not 

 depress d{D)l(h immediately because it will require a finite time for (C) 

 to decrease. When there are more steps past the point of inhibition or when 

 the system is properly compartmentalized, there may be a lag period before 

 any effect on d(D)l(lt can be measured. Simultaneously, (B) will increase 

 and the drop in (C) will be progressively counteracted until the final steady 



