184 



5. DETERMINATION OF MECHANISMS AND CONSTANTS 



in log-log coordinates are given for competitive inhibition in Figs. 5-21 and 

 5-22 using the following rearrangement of the nsiial inhibition Eq. 3-13: 



(I) = K, 



1 



+ 





1 



(S) 



(5-35) 



This is seen to be a variation of the single-curve plot of Eq. 5-7 with the 

 terms in i transposed. Thus it has no advantage as a method for the deter- 

 mination of constants but can be used for visually demonstrating the 

 combinations of substrate and inhibitor concentrations to produce specific 

 degrees of inhibition. When the inhibitor reacts with the substrate, straight 

 lines are obtained in the log-log plot, which may help to distinguish this 

 type of inhibition from truly competitive situations, as indicated in Fig. 5-23. 



lOOmM 



lOOmM 



Fig. 5-21. Competitive inhibition isobologram (Eq. 5-35) plotted on 

 linear scales. Xj = 1 milf and Ki = 0.1 mil/. 



MUTUAL DEPLETION SYSTEMS 



When the concentration of free inhibitor is reduced by combination of 

 the inhibitor with the enzyme, the characteristics of the curves plotted by 

 the usual procedures are altered in most cases. We have considered only 

 systems in zone A^ and some comment on zone C ^ kinetics is needed. Inas- 



