STUDIES ON CHEMICAL MODIFICATION OF STAPHYLOCOCCAL ENTEROTOXIN B .I. ALKYLATION AND OXIDATION OF METHIONINE RESIDUES

The methionine residues in staphylococcal enterotoxin B have been modified with iodoacetic acid and H2O2. Kinetic analysis of the interaction between iodoacetic acid and enterotoxin B at pH 2.7 reveals that four of the eight residues react at a faster rate. The oxidation of enterotoxin B with H2O2 was much faster at pH 2.3 than at pH 2.7. At pH 2.3 seven methionine residues were oxidized. Immunochemical and fluorimetric analyses of the modified enterotoxin B indicate that the conformation of the protein is changed when more than six of the methionine residues are modified by either of these methods. The emetic activity of the toxin was also lost when six methionine residues were modified. Since the modification affects both the biological activity and conformation, the role of methionine residues in staphylococcal enterotoxin B is discussed. © 1969.