Covalent structure of the beta chain of cholera enterotoxin

The complete amino acid sequence of the beta chain of cholera enterotoxin was determined: NH2-Thr-Pro-Gln-Asn-Ile-Thr-Asp-Leu-Cys-Ala-Glu-Tyr-His-Asn-Thr-Gln-Ile-His-Thr-Leu-Asn-Asn-Lys-Ile-Phe-Ser-Tyr-Thr-Glu-Ser-Leu-Ala-Gly-Lys-Arg-Glu-Met-Ala-Ile-Ile-Thr-Phe-Lys-Asn-Gly-Ala-Thr-Phe-Gln-Val-Glu-Val-Pro-Gly-Ser-Gln-His-Ile-Asp-Ser-Gln-Lys-Lys-Ala-Ile-Glu-Arg-Met-Lys-Asn-Thr-Leu-Arg-Ile-Ala-Tyr-Leu-Thr-Glu-Ala-Lys-Val-Glu-Lys-Leu-Cys-Val-Trp-Asn-Asn-Lys-Thr-Pro-His-Ala-Ile-Ala-Ala-Ile-Ser-Met- Ala-Asn-COOH. The sequence was obtained from automated sequence analysis of intact beta chain, cyanogen bromide fragments, and a fragment generated by cleavage at a single tryptophan with 2-(2-nitrophenylsulfenyl)-3-methyl-3-bromoindolenine as well as from manual sequence analysis of tryptic peptides using 5-dimethylaminonaphthalene-1-sulfonyl-monitored Edman methodology. The tryptic peptides accounted for all 103 residues established for the complete primary structure.