Amino Acid Sequence of C‐Terminal Fragment of Hog Pepsin

The C‐terminal fragment of hog pepsin, which had been obtained in the preceding study on the cyanogen bromide hydrolysate of this protein, was subjected to sequential studies. The 37‐residue peptide was digested in independent experiments by trypsin, chymotrypsin, and pepsin, and the amino acid sequence of the arising peptides was determined. In parallel experiments the sequence of seventeen amino acid residues in the N‐terminal region of the peptide was established by the Edman degradation technique. The obtained data permit the C‐terminal peptide of hog pepsin to be ascribed the amino acid sequence Asp‐Val‐Pro‐Thr‐Ser‐Ser‐Gly‐Glu‐Leu‐Trp‐Ile‐Leu‐Gly‐Asp‐Val‐Phe‐Ile‐Arg‐Gln‐Tyr‐Tyr‐Thr‐Val‐Phe‐Asp‐Arg‐Ala‐Asn‐Asn‐Lys‐Val‐Gly‐Leu‐Ala‐Pro‐Val‐Ala. These results extend and partly correct our previous knowledge of this region of the pepsin molecule as recorded in literature. The problem of the tryptophan content of pepsin is briefly discussed.