Biological activity and complementation of the two peptides of staphylococcal enterotoxin B formed by limited tryptic hydrolysis.

Tryptic hydrolysis after reduction and carboxamidomethylation of staphylococcal enterotoxin B cleaved the single susceptible bond located between the 2 half-cystines of the molecule, Lys-Thr at positions 97 and 98 (Spero, L., Warren, J. R., and Metzger, J. F. (1973) J. Biol. Chem. 248, 7289-7294). The product remained as a single particle but was separated into the two constituent peptides by denaturants, and purification of the two fragments was accomplished by chromatography on CM-cellulose in 8 M urea. Antigenic activity was exhibited by the separated peptides after dialysis of urea solutions against dilute buffer, but was very labile. No emetic activity in rhesus monkeys was found for either separated peptide. The derivative behaved as two random coil peptides in 6 M guanidine hydrochloride but upon removal of guanidine refolded to a single molecular entity. Viscosity and unfolding kinetics in 1.5 M guanidine indicated physical identity of the recombined peptides with the derivative prior to treatment with guanidine. Three biological measures (serological, mitogenic, and emetic activity) were also essentially unaltered for the recombined material. Since these biological activities are dependent upon different aspects of enterotoxin structure, it is concluded that the recombined derivative was restored to its original conformation.