JOHN H. NORTHROP 



499 



TABLE VI. 



Influence of the Gelatin Concentration on the Retardation Caused by the Presence 

 of a Constant Amount of Inhibiting Substances. 



* Calculated by equation C = . E = 10.1, I = 3.0 (units inhibitor), 



K -f- o 



K = 0.5 (derived by assuming that inhibitor-enzyme compound is very little 



dissociated). 



E S 



t Calculated by equation C = -r;^, = 10.1, K" = 3.4, derived by assum- 



A + o 



ing that the amount of inhibitor combined with the enzyme is negligible compared 

 to total amount of inhibitor, and that inhibitor enzyme compound is widely 

 dissociated. 



This equation is derived as follows: Let S = total substrate concentration, 

 E total enzyme concentration, C enzyme combined with substrate, / enzyme 

 combined with inhibitor, and / total inhibitor. 



Then if the amount of substrate combined with the enzyme is negHgibly small 

 compared to the total amount of substrate and if the same is true of the inhibitor, 

 the mass action expressions for the two equilibria are 



S{E -C -J) = KC(l) I{E -C -J) = kJ{2) 

 _ E S - KC - SC 

 S 



Substituting this value of J in (2) and simplifying C = 



E S 



IK 



in which 



+ K+S 



R 



K = equilibrium constant of substrate-enzyme equilibrium, and k = equilibrium 

 constant for inhibitor-enzyme compound. Since in this experiment /, K, and k 



E S 



are all constant they may be combined to a new constant K" and C = 



K" + S 



