[Isolation and characterization of erythrogenic toxins. VII. Study of the erythrogenic toxin type C produced by...

Erythrogenic toxin (ET) type C was purified from culture filtrates of Streptococcus pyogenes strains NY 5, T 18, and AT 13. Methods used included ammonium sulfate precipitation, phosphate precipitation, column chromatography on CM-Sepharose and Sephadex G 100, and isoelectric focusing in Sephadex gel. The molecular weight was determined by SDS gel electrophoresis as 25,500. The preparation reacted only with homologous antiserum (anti-C), but not with antitoxins types A or B in double diffusion tests. The isoelectric point was determined to be 6.8 by analytical isoelectric focusing. Also the amino acid composition was determined. The toxin was found to be mitogenic (as well as pyrogenic and toxic for rabbits). The ET type C is digested by trypsin, pepsin, chymotrypsin and Pronase E, but is rather stable when treated with papain or streptococcal proteinase.