N‐Terminal Fragment of Hog Pepsin

One of the peptide fragments obtained in a preceding study of the cyanogen bromide hydrolysate of S‐sulfo‐pepsin has been investigated in more detail. The peptide was purified by ion‐exchange chromatography and obtained in homogeneous form. It contains 158 amino acid residues, among their number the only histidine residue of pepsin and two half‐cystine residues. Evidence was obtained that the peptide is derived from the N‐terminal region of the molecule of hog pepsin. The peptide was reduced by 2‐mercaptoethanol and converted into its S‐(β ‐amino‐ethyl)‐cysteinyl derivative. From the tryptic digest of this derivative a 105‐residue peptide containing N‐terminal isoleucine was isolated which represents the N‐terminal segment of the pepsin molecule.