INHIBITION OF ENZYMES 



795 



group with p^a near 4.4 could be the benzoate group of p-MB, particularly 

 as no inflection is shown here in the K„, curve. However, as Fernley clearly 

 pointed out, one must proceed with caution because of the many complexes 

 possible with the mercurial, and particularly the buffer effects. It seems 

 unlikely that the decrease in K, above pH 5 is due to complexing with OR- 

 ions entirely, but it might be the result of reactions with the buffer; the sim- 

 ilar inflection for K„^ makes it reasonable that an enzyme group is involved. 

 The results with PM are quite different than with Hg++ or p-MB (Fig. 7-14); 



100 



80 



60 



40 



20 



-20 



Fig. 7-14. Effects of pH on the inhibitions of ^-glu- 

 curonidase by heavy metal ions. (From Fernley, 1962.) 



PM is generally less inhibitory than p-MB, does not increase Kf„ whereas 

 p-MB does, facilitates the formation of the ESg complex (favoring substrate 

 inhibition) whereas p-MB does not, and increases the pH^pt whereas Hg++ 

 and p-MB decrease it. The marked effect of PM on substrate inhibition is 

 shown in Fig. 7-16 but no explanation is available. There is certainly a need 

 for more accurate comparisons of the different mercurials, not only with 

 respect to pH effects but generally. The different curves obtained with Hg++ 

 and PM acting on pancreatic amylase (Fig. 7-17) are intriguing and one 

 feels that an explanation of such phenomena might well aid in our under- 



