Effect of phytate on the in vitro activity of digestive proteinases

Phytate inhibits the action of pepsin on the proteins but does not affect the pepsin hydrolysis of a low molecular weight substrate, acetyl-L-phenylalanyl-3,5-diioclo-L-tyrosine. The inhibition is maximal at pH 2-3 and drops to zero when the pH is increased to 4.0-4.5. Trypsin hydrolysis of both a low molecular weight substrate (benzoyl-D,L-arginine p-nitroanilide) and proteins is insensitive to the presence of phytate. The proteins tested include RNase and lysozyme charged positively at the pH of the trypsin hydrolysis. Thus, the inhibitory action of phytate is manifested only when it is bound with the protein substrate. The overall positive charge of protein is not a sufficient condition of phytate binding. Evidently, the protonation of protein carboxylate groups is also required