The complete amino acid sequence of monkey progastricsin.

The complete amino acid sequence of progastricsin from the Japanese monkey (Macaca fuscata) was determined. Progastricsin is composed of 374 residues, including the gastricsin moiety of 331 residues and the activation segment of 43 residues. Upon activation under acidic conditions, progastricsin was converted to gastricsin via the intermediate protein species. NH2-terminal sequence determination of these protein species enabled us to deduce the NH2-terminal 78-residue sequence of progastricsin, including the 43-residue activation segment. The complete sequence of the gastricsin moiety was determined using peptide fragments obtained by several chemical and enzymatic cleavages. The molecular weight of progastricsin was determined to be 40,785. As compared with pepsinogen A of the same monkey species, deletion of 4 residues and insertion of 5 residues were observed. Although monkey progastricsin and pepsinogen A have highly homologous sequences around the two active site aspartyl residues, the homology between these proteins is rather small (49% identity). This indicates that progastricsin diverged from pepsinogen A in the early phase of the evolution of gastric aspartyl proteinases.