The amino-terminal sequence of porcine pepsinogen.

Amino acid sequence studies were performed on (a) peptides obtained from tryptic hydrolysates of succinyl pepsinogen and (b) those isolated from a peptide mixture formed when pepsinogen is activated to pepsin. These peptides taken together with tryptic peptides obtained from reduced carboxymethylated pepsinogen establish the complete sequence of 41 residues at the NH&erminal end of the single polypeptide chain of porcine pepsinogen. The amino acid composition of this segment is in excellent agreement with that estimated from the differences between the amino acid compositions of pepsinogen and pepsin. The positions of the 9 lysines, ‘the 2 histidines, and the 2 arginines have been located and should allow a further assessment of the contribution of the basic’amino acid residues to stabilization of the zymogen. In addition, it is proposed that pepsin is formed after cleavage of a glutamylisoleucyl bond between residues 41 and 42 of pepsinogen.