PHENOL OXIDASES 



299 



of ionization at the experimental pH of 5.2 varies. It was found that the 

 inhibition by benzoate decreases with rise in the pH (see tabulation) and 



pH 



% Inhibition by benzoate (0.0123 mil/) 



% Un-ionized 



5.2 

 5.8 

 6.4 

 7.0 



56 



28 



9.0 

 2.5 

 0.6 



0.2 



similar results were obtained with some substituted benzoates. This was 

 interpreted to mean that the un-ionized form of the inhibitor is the active 

 one, for example that benzoic acid is the inhibitor and not the benzoate 

 ion. The relative binding energies have been recalculated (Table 2-7) on 

 this basis and a somewhat different order of potency is obtained. This il- 



Table 2-7 



Inhibition of Mushroom Phenol Oxidase Corrected for the State of Ionization 



OF THE Inhibitors " 



° Relative binding energy corrected on the basis that the un-ionized forms of the 

 inhibitors are active. The ionization constants were obtained from Dippy (1939); 

 inhibition data are given in Table 2-6 (Kuttner and Wagreich, 1953.) 



