762 



15. EFFECTS OF VARIOUS FACTORS ON INHIBITION 



oi K- . In all cases where there is inactive enzyme, the nsual determinations 

 of the inhibitor constant will be in error by an amount dependent on the 

 value of K. With respect to the effects of changes in the temperature, the 

 inhibition will increase as the temperature rises due to the fall in K and 

 the increase in E^ with which the inhibitor can combine. By appropriate 

 graphical analysis it would be theoretically possible to determine the 

 changes in both K and K^' but the temperature range would have to be 

 sufficient to allow accurate evaluation. 



Case II: inhibitor combines only with E,, — competitive 



K, E„S -> E„ + P 



A' 



Erf =± E„ 



^> EJ 



The rate and inhibition equations may be shown to be: 



F,„(S) 



Vi = 



(I) + K, 



1 (S) 



1 H h -— - 



^ K ^ K, 



(15-21; 



(15-22) 



(15-23) 



As K approaches infinity, the inhibition becomes completely competitive, 

 and when K is small, both the uninhibited and inhibited rates decrease. 

 Graphical procedures yield plots characteristic of competitive inhibition 

 but from which the calculation of K, will be in error. A rise in temperature 

 will cause a fall in the inhibition. 



Case III: inhibitor combines only with E^ — nmicompetitive 



E„ + P 



K. 



K 



Ed ;^ Ea 



E„S ^K, 



^ 



E.SI 



(15-24) 



EJ A'. 



For completely noncompetitive inhibition the equations take the forms: 



^'"^^^ (15-25) 



(15-26) 



(I) + K, + 



KiKs 



