CHEMICAL MODIFICATION OF AMINO GROUPS IN STAPHYLOCOCCAL ENTEROTOXIN B

Chemical modification of amino groups in staphylococcal enterotoxin B with acetic anhydride, succinic anhydride, 2-methylisourea, and potassium cyanate has been studied. Neither the emetic activity nor the combining power of the antigen-antibody reaction was altered when 90% of lysine residues were guanidinated. The combining power of the acetylated, succinylated, and carbamylated enterotoxin B with antibody, however, was reduced. The decrease in the combining power of enterotoxin B after modification with acetic anhydride or succinic anhydride is directly proportional to the amino groups modified. Monkey feeding tests of the acetylated and succinylated enterotoxin B reveal that the loss of toxicity is closely related to decrease of the antigen-antibody reaction. Physicochemical studies on the modified enterotoxin B indicates that enterotoxin B undergoes a molecular expansion after acetylation and succinylation. Since guanidination did not alter the biological activity of the toxin, it is concluded that the reduction of the biological activity after acetylation and succinylation is due to a decrease of the net positive charges in the protein. The role of the positive charges on the conformation and biological activity of enterotoxin B is discussed. © 1969, American Chemical Society. All rights reserved.