602 



12. RATES OF INHIBITION 



netics would be too complex to be interpretable by concentration-time re- 

 lationships. 



The problem here is the same as in the interpretation of any kinetic 

 data — before the results can be related to any mechanism of inhibition, 

 it must be definitely shown that the time intervals measured refer to the 

 primary inhibition. There are several factors that can lead to straight lines 

 when log (I) is plotted against log t. Penetration of a substance into a cell 

 would be expected to conform to this pattern. Indeed, it has been shown 



1000 



1000 



Fig. 12-44. Log-log plots of concentration-time curves for inhi- 

 bition of enzymes. A', = 5 ml/, k^= 1, C = 700, and i = 0..5. 

 Curve A, irreversible inhibition (Eq. 12-92); curve B, reversi- 

 ble inhibition (Eq. 12-94). 



that the entrance of cresyl blue into Nitella cells is expressed by the Eq. 

 [(dye) — 0.7](^ — 0.6) = 102, where the concentration is in units of 10^^ M 

 and the time is in minutes (Irwin, 1925), and that the log-log plots are lin- 

 ear. Variation in a population of cells could also provide data on killing 

 rates by inhibitors that would fit such a formulation, and it is quite likely 

 that the trypanocidal action of the arsenicals (Hawking, 1938) discussed 

 in the previous section belongs in this category, inasmuch as fixation of 

 the inhibitors seems to be quite rapid. 



The value of the exponential n in equations of type {I)"t = C is also not 



