Evidence for Two Molecular Forms of Streptococcal Erythrogenic Toxin

Two molecular forms of streptococcal erythrogenic toxin have been isolated by DEAE‐cellulose chromatography. These two forms exhibit the same biological and immunological properties. They have the same sedimentation coefficient s20= 2.52. Molecular weight is about 30 000. The protein is made of a single polypeptide chain with glutamic acid as N‐terminal amino acid. Exposure to 2‐mercaptoethanol induces conversion to a single form. The possibility that the different molecular forms arise from the binding of small molecules of different charge through a sulfhydryl group of the protein is discussed.