RATES OF IXHIBITION OF PURE ENZYMES 



547 



manner. This is also apparent from the fact that iodoacetate, o-iodosoben- 

 zoate, and iV-ethylmaleimide do not inhibit the lactate dehydrogenase. It 

 was tentatively concluded that two sulfhydryl groups per dehydrogenase 

 molecule were reacted with p-CMB after 30 min of incubation. 



TIME- 



MIN 



Fig. 12-9. Logarithmic plot of the inhibition of phisma cho- 

 Hnesterase by HgClj for the determination of u and k^. 



A comparison of the rates of inhibition of succinoxidase by a variety 

 of sulfhydryl reagents was made by Slater (1949) and the results are shown 

 in Fig. r2-12. The striking difference between p-CMB and the other inhibi- 

 bitors should be noted. The reaction of p-CMB with the enzyme was prac- 

 tically instantaneous, whereas the other inhibitors required 30 to 60 min 

 to reach maximal inhibition. The two substances inhibiting by oxidation 

 of the sulfhydryl groups (o-iodosobenzoate and oxidized glutathione) pro- 

 duced their effects particularly slowly. The rate of inhibition with o-iodoso- 

 benzoate at 160 (piaf_ 12-13) exhibited two phases, a rapid one complete 



