800 



7. MERCURIALS 



Case C: Inhibition develops only after so many SH groups have reacted. 



(1) The most reactive SH groups are not related to the activity of the 

 enzyme, but the less readily available ones are. 



(2) None of the SH groups is directly related to the activity, but when 

 a sufficient number are reacted the enzyme is structurally altered so that 

 inhibition appears. 



These situations may be distinguished sometimes by determining the 

 reversibility of the inhibition, but occasionally denaturation is reversible. 



Case D: Inhibition develops completely before all the SH groups react. 

 (!) The most reactive SH groups are at the active center and when they 



Fig. 7-19. Illustrations of the various relation- 

 ships between the reaction of enzyme SH 

 groups with mercurials and the inhibition of 

 enzyme activity. These are all extreme cases 

 and intermediate situations can also occur. 

 p-MB has been designated but any mercurial 

 may be used. The solid lines show the inhi- 

 bition and the dashed lines the reaction with 

 SH groups; i is the fractional inhibition and r 

 is the fraction of the total SH groups reacted. 



