596 



12. RATES OF INHIBITION 



t„i is the minimal time in which the effect can Vje produced whatever the in- 

 hibitor concentration (Fig. 12-37). Either (!),„ or ^,„ may be negligible and 

 can be omitted; indeed, the data are occasionally expressed adequately by 

 the simple equation: 



(1)"/ = C 



Taking the logarithm of each side and transposing: 



log t = log C — n log(l) 



(12-90) 



(12-91] 



(I) 



Fig. 12-37. Illustration of a plot of Eq. 

 12-89 where (1)^ is the minimal inhibitor 

 concentration to produce an effect and 

 <„( is the minimal time in which an effect 

 can be produced. 



so that a plot of log t against log (I) should give a straight line of slope 

 — n and intercept log C if this equation is obeyed (Fig. 12-38). The effects 

 of variation in the constant n on the form of the curves is shown in Fig. 

 12-39, for which the log-log plots are presented in Fig. 12-40. As n increases, 

 the curves approach more readily the (I) axis and the minimal radius of 

 curvature decreases. All curves must pass througii the point where (I) is 

 unity because the exponential factor has no significance here. The value 

 of n is easy to determine, as is the value of C; the difficulty arises when 

 an attempt is made to place some physical interpretation on these constants. 

 It is evident that if (!),„ or t,„ or both are significant, a plot of log t against 

 log (I) will not give a straight line (Fig. 12-41, curve A), so that in order 

 to test the validity of this type of equation in such cases, it is necessary 

 to plot log [(I) - (I),J or log {t - tj (Fig. 12-41. curve B). 



