Amino acid sequence of cyanogen bromide fragments CB4 and CB6 of hog pepsin

Abstract

By the analyses of chymotryptic, and thermolytic peptides the amino acid sequence was determined of cyanogen bromide fragment CB4 representing the region of the pepsin chain between the N-terminus and methonine-residue I: Ile-Gly-Asp-Glu-Pro-Leu-Glu-Asn-Tyr-Leu-Asp-Thr-Glu-Tyr-Phe-Gly-Thr-Ile-Gly-Ile-Gly-Thr-Pro-Ala-Gln-Asp-Phe-Thr-Val-Ile-Phe-Asp-Thr-Gly-Ser-Ser-Asn-Leu-Trp-Val-Pro-Ser-Val-Tyr-Cys-Ser-Ser-Leu-Ala-Cys-Ser-Asp-His-Asn- + Gln-Phe-Asn-Pro-Asp-Asp-Ser-Ser-Thr-Phe-Glu-Ala-Thr-Ser-Gln-Glu-Leu-Ser-Ile-Thr-Tyr-Gly- + Thr-Gly-Ser-Met. The serine residue (Ser) in position 68 of pepsin is phosphorylated. By sequential analysis of chymotryptic, tryptic, and thermolytic peptides the amino acid sequence was determined of cyanogen bromide fragment CB6 representing the region between methionine residues II and III in the pepsin chain: Asp-Gly-Glu-Thr-Ile-Ala-Cys-Ser-Gly-Gly-Cys-Gln-Ala- + Ile-Val-Asp-Thr-Gly-Thr-Ser-Leu-Leu-Thr-Gly-Pro-Thr-Ser-Ala-Ile-Ala-Asn-Ile-Gln-Ser-Asp- + Ile-Gly-Ala-Ser-Glu-Asn-Ser-Asp-Gly-Glu-Met. The aspartic acid residue (Asp) in position 16 of this fragment is identical with the residue reacting with diazo inhibitors which forms a part of the active center of the enzyme. Both half-cystine residues of fragment CB4 and fragment CB6 are linked to one another by a disulfide bond in native pepsin.