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. [ABSTRACT FROM AUTHOR]