798 



7. MERCURIALS 



lessening of the inhibition. The inhibition of NADH dehydrogenase by p- 

 MPS is weaker in phosphate than in THAM buffer, and this could again be 

 due to complexes with phosphate (Minakami et al., 1963). Despite the pau- 

 city of experimental information, the effects of ions and buffers should be 

 more frequently taken into account in the use of the mercurials. In addition 

 to the ionic effects just described, certain specific actions have been noted, 



100 



50 



25 



X 

 ACT 



rONIC STRENGTH ON 

 HgClj INHIBITION 

 (HgClj).0 05mM 



'0 0.01 



IONIC STRENGTH 



0.02 



0.03 



0.04 



005 



Fig. 7-18. Inhibition of trypsin by Hg++ and the ef- 

 fect of ionic strength. (From Green and Neurath, 1953.) 



especially with ATPase (Novikoff et al., 1952; Lardy and Wellman, 1953; 

 Sacktor et al, 1953), where the concentrations of Mg++ and Ca++ determine 

 to some extent the susceptibility of the mitochondrial enzyme to mercurials, 

 generally Mg++ lessening the inhibition, although here one may be dealing 

 with more than one enzyme. 



Titration of Enzyme SH Groups 



The primary purpose of a titration with a mercurial is to determine the 

 number of reactive SH groups which an enzyme possesses, either normally 

 or after being treated in various ways (e.g., denatured with urea, guanidine, 



