VAUIATION OF INTRACELLULAR INHIBITION WITH pH 



715 



concentration of I in terms of the total external inhibitor concentration is 

 given by: 



(I.)»(H)„ 



ah = 



o//(H), 



(14-153) 



The charged form of the inhibitor is often the active form within the cell 

 and thus its concentration will frequently determine the degree of inhibi- 

 tion. The expression for (HI), in terms of the total external concentration 

 is simply: 



(!.)<, 



(HI), 



oJhi 



(14-154) 



and the total concentration of the inhibitor in the cell is given by: 



J/(I()o(H)<, 



(I.),- = 



o//(H), 



14-155) 



These concentrations are plotted for an hypothetical case in Fig. 14-16. 



There are two particularly important points to note in these curves. The 



first is that the intracellular concentration of the ionic form varies with the 



lOCX) 



COMPLETELY BUFFERED CELLS 

 (pHi=6.8) 



Fig. 14-16. Variation of the intracellular inhibitor concentration with pH 



(scheme 14-150). The cells are completely buffered at pH, = 6.8. (I^)o = 10 



m3I, A'„ = 10-5, and (H), = 1.6 X 10-' 31. 



