Acetylation of Pepsin and Pepsinogen

Abstract 1. Acetylimidazole, an acetylating reagent of proteins reacts both with the proteolytic enzyme, pepsin, and its zymogen, pepsinogen. 2. When reacted with pepsin, the proteolytic activity decreases whereas the hydrolysis of the synthetic substrate, N-acetyl-dl-phenylalanyldiiodotyrosine, increases 2.5-fold. These changes can be reversed by deacetylation with hydroxylamine. 3. Acetylation of pepsinogen leads to a reduced susceptibility to activation as reflected by its potential pepsin activity and a decreased hydrolysis of the synthetic substrate. 4. With the aid of difference spectra and hydroxamate formation, it was ascertained that 8 to 10 tyrosine residues were acetylated. 5. In contrast to pepsin, it was demonstrated that in acetylpepsinogen 4 to 5 e-amino groups of the lysine residues were acetylated in addition to tyrosines. 6. These results are correlated with some of the conformational characteristics of the two proteins.