The Primary Structure of Staphylococcal Enterotoxin B

Cyanogen bromide treatment of reduced, aminoethylated enterotoxin B yielded seven major peptides plus homoserine and homoserine lactone, as was expected from the number of methionine residues present in the enterotoxin B molecule. The cyanogen bromide peptides were fractionated on Sephadex G-50 and further purified by rechromatography on Sephadex G-50 or paper electrophoresis at pH 1.9. They contained a total of 239 amino acid residues. Tryptic peptides of each of the cyanogen bromide peptides were purified and their amino acid composition was determined. The order of these peptides in each cyanogen bromide peptide and the order of the cyanogen bromide peptides in enterotoxin B were established. Based on the information from tryptic, chymotryptic, and cyanogen bromide peptides, the complete amino acid sequence of enterotoxin B was established. Staphylococcal enterotoxin B is a single polypeptide chain containing 239 amino acid residues.