Primary structure of porcine pepsin. III. Amino acid sequence of a cyanogen bromide fragment, CB2A, and the complete structure of porcine pepsin.

The complete amino acid sequence of porcine pepsin (EC 3.4.4.1) was constructed from the sequence of five cyanogen bromide fragments. The sequence of one of these fragments, CB2A, is reported here. The sequences of 4 other fragments are known from previous work. Porcine pepsin contains 327 residues with three structural variants. The active center aspartyl residue, which reacts with 1,2-epoxy-3-(p-nitrophenoxy)propane (Chen, K. C. S., and Tang, J. (1972) J. Biol. Chem. 247, 2566-2574), is located at residue 32. Another active site aspartyl residue, which reacts with diazo inactivators (Bayliss, R. S., Knowles, J. B., and Wybrandt, G. B. (1969) Biochem. J. 113, 377-386, IS LOCATED AT RESIDUE 215. The sequences around these 2 aspartyl residues are apparently homologous to each other. The sequences around the tryptophanyl residues at positions 39, 141, 181, and 300 are also homologous to one another. These homologous sequences could be genetic in origin. Fragment CB2A which contains 119 residues was constructed from the peptide sequences resulting from six proteolytic digestions and chemical cleavage at tryptophanyl bonds.