722 



14. EFFECTS OF pH ON ENZYME INHIBITION 



inhibition studies point to the same conclusion. The effects of malonate 

 on seven plant tissues (Fig. 14-19) and of iodoacetate on yeast, barley 



Fig. 14-18. Penetration of HjS into Valonia cells at different ex- 

 ternal levels of the pH. The circles show the experimental points 

 obtained by Osterhout (1925) and the curve shows the per cent of 

 the total sulfide in the medium that is H-S. 



roots, and oat coleoptiles (Fig. 14-20) vary with external pH in a manner 

 that suggests the undissociated acids to be the permeant forms. The inef- 

 fectiveness of malonate in the pH range above 7 has been noted in work 

 with many tissues (e.g., Webb, 1950 a) and the actions that have been ob- 

 served with high concentrations are probably due to effects on the mem- 



