INHIBITION OF ENZYMES 



821 



Reversal of Mercurial Inhibition 



The general treatment of the reversal of enzyme inhibition by substances 

 binding the inhibitor (page 1-615) wiU now be extended to those situations 

 often encountered in studies of the mercurials. The most common reversors 

 are thiols, e.g., cysteine, glutathione, mercaptoethanol, mercaptoacetate, 

 and dimercaprol (BAL), and the reduction in the inhibition can be consid- 

 ered as a transfer of the mercurial from enzyme SH groups to the reversor 

 (R) SH groups. In many reactivation experiments the concentration of free 

 mercurial is very small and the reversal reaction can be written as: 



EI + R ±5 E 



(E,) - X (Rt) - X X 



+ 



RI 



X 



(7-13) 



If the enzyme is initially completely inhibited, (EI) = (EJ, and the final 

 equilibrium concentrations are as written under the equation. The equilib- 

 rium is characterized by the following constants: 



(EI)(R) [(E,) -x] [(Rt)-x] 



(E) (RI) 



(E) (I) 

 (EI) 



K, 



(R) (I) 

 (RI) 



K 



= Kr 





(7-14) 



Fig. 7-30. Effects of p-MB on myosin ATPase 

 at 0° and 25°, and in the presence of 2,4-di- 

 nitrophenol. The ATPase activity is given 

 as /^moles P,/mg/min. (From Gilmour and 

 Griffiths, 1957.) 



