Complete amino acid sequence of hog pepsin

The amino acid sequence of hog pepsin or of some parts of its polypeptide chain has been studied in a number of laboratories. The most recent summary of the results obtained is presented in the 1972 issue of the Atlas of Protein Sequence and Structure [ 11. Our aim has been to determine the complete covalent structure of this enzyme and thus to provide, together with the complete structures of bovine trypsinogen [2] and chymotrypsinogen [3] elucidated in this laboratory earlier, complete and independent sequence information on the fundamental proteolytic enzymes of the digestive tract. The determination of the complete structure of the whole molecule was based on the results of sequential studies on large fragments designated CB [4] obtained by cyanogen bromide cleavage of pepsin at its four methionine residues [5] (fig. 1). The studies on the individual cyanogen bromide fragments were begun after the determination of the disultide bonds of the 6 half-cystine residues of pepsin [6]. The complete amino acid sequence of fragment CBl [7], representing the 37-residue C-terminal part of the molecule, was determined. Later, the 55residue N-terminal amino acid sequence of pepsin [8,9] was