Chemistry of allergens. XXII. Isolation and characterization of three new antigens from the dialysates of six successive pepsin hydrolyses of beta-lactoglobulin.
Twelve new antigens previously have been demonstrated in the pepsin digests of milk proteins. The term "new antigen" is defined as an antigen with a specificity distinct from that of the protein from which it was generated. Three new antigens (alpha-, beta-, and D2i) polypeptides and one nonantigenic gamma-polypeptide have been isolated from the dialysates of six successive pepsin hydrolyses of beta-lactoglobulin. The alpha- and beta-polypeptides were 1/5 and D2i was 1/10-1/20 as potent immunogens as precursor beta-lactoglobulin as determined by the Schultz-Dale technique. The minimum observed amounts of new antigen eliciting maximum response of uterine strips in the Schultz-Dale tests were: alpa-D2, 50 ng; beta-D2, 15 ng; beta-D3; 10 ng; and D2i, 1,000 ng. Except for the alpha-polypeptide, the amino acid contents of the polypeptides differed markedly from that of beta-lactoglobulin. The beta-polypeptide has been tentatively identified as a 33 amino acid fragment of beta-lactoglobulin (3,910 daltons). The gamma-polypeptide has been tentatively identified as a 12 amino acid fragment of beta-lactoglobulin (1,372 daltons).