680 14. EFFECTS OF pH ON ENZYME INHIBITION 



(c) Noncompetitive inhibition on the active form. HE {scheme 14-59) 



1 + 



K. 



a) 



+ 



F™(S) 



ihe + 





i+^(i+A/) 



(I) 



(I)(l - ^)/^ - (S): 



(I)(l 



K, 



V K 



KiKaK, 



1 -\ 



(S) 



(H)[(S)+Z, 



(14-89) 

 (14-90) 

 (14-91) 



In a plot of type A, as in (a) above, the slope depends on the pH whereas 

 the intercept does not. If Kj is determined from rhe intercept, rather than 

 from the slope, no pH correction need be made. The slope of a plot of type 

 D, however, is the same as for the nonionizing case, and depends on (S) 

 and not pH. The higher (S), the greater the deviation from the competitive 

 slope, but no problem is involved in the calculation of K^. The type F 

 plot will be quite diiferent in configuration, compared to the nonionizing 

 case, because (S) here occurs in the denominator, but the interce]~)t gives 

 the true K^ and does not depend on the pH. 



(d) Noncompetitive inhibition on the active form E {scheme 14-62) 



IM - 1/(S): 



1/t'.- - (I): 



1 



f: 



1 



1 -h 



K, 



a) 



+ -. 



/i, 



F„.(S) 



/; + 





1+-^(1+//) 



{I) 

 F,„A\. 



1 + 



(S) 



(I)(l - i)ii (S): ^^^^^ ■ '^ = /i, + 



K.KM) 



(14-92) 



(14-93) 



(14-94) 



The equations here are the same as in (c) except for the reverse dependence 

 on pH and the calculation of K^ presents the same ]5roblems. 



(e) Noncompetitive inhibition on the inactive form E {scheme 14-65) 



+ ^ 





fne' + 



Ka{l) 



1 +A/ 



= fe'Ki 



(S) 



+ 



A^(H) 



F„,A,(S)(H) 



A, (H)(S) 



KaK, 



(14-95) 

 (14-96) 

 (14-97) 



