670 



14. EFFECTS OF pH ON ENZYME INHIBITION 



E or HE. The inhibitor can then combine competitively or noncompeti- 

 tively with either active form of the enzyme, E or HE, or with the non- 

 active form of the enzyme. There are thus six possible situations for this 

 simplest of systems. 



(a) HE is active form of enzyme: I combines with HE competitively. 



K, HES ^ HE + P 



E =± HE 



(14-52) 



Ki HEI 



In each case, the inhibited rate and the fractional inhibition will be given; 

 the implications will be discussed when the six situations have been pre- 

 sented. It must be remembered that the uninhibited rate is now given bv: 



F„(S) 



(S) + fhe'Ks 



The inhibited rate may be written as: 



F„(S) 



(14-53) 



(S) + K, 

 and the fractional inhibition as: 



fne 



(I) 





(14-54) 



(I) + K, 



the 





(14-55) 



(b) E is active form of enzyme: I combines with E competitively. 



A, ^ E8 -^ E + P 



A'„ 



HE =± E 



'^ 



(I) + K, 



fe + 





(14-56) 



(14-57) 



(14-58) 



