Biological activities of the peptides of staphylococcal enterotoxin C formed by limited tryptic hydrolysis.

Staphylococcal entertoxin C1 is converted to a doubly cleaved molecule by trypsin digestion with one of the scissions internal to the disulfide loop and one external to it. The larger, disulfide-containing polypeptide (Mr = 22,000) exhibited excellent binding to antiserum to the intact enterotoxin. The residual amino terminal fragment (Mr = 6,500) also bound to this antibody but only weakly. Only the carboxyl terminal carboxamidomethylated moiety of the 22,000 Mr polypeptide (Mr = 19,000) combined with anti-enterotoxin C1. Both the 22,000 Mr and 6,500 Mr polypeptides could partially inhibit the binding of entertoxin C1 to its antibody in a competitive system. It is suggested that enterotoxin C1 possesses three major antigenic determinants, two on Cam 19,000 and one on the 6,500 Mr fragment.