Peptides from the Site of Rabbit Antibody: Anti-Azophenyltrimethylammonium Antibody

[摘要] A tyrosine peptide which appears to be derived from the combining site of an anti-azophenyltrimethylammonium antibody was isolated and the amino acid sequence was determined. Binding studies showed that the antibody was inactivated by iodination and that the attack was in the site, since the presence of the hapten, phenyltrimethylammonium ion, during iodination prevented the loss of sites.The peptide from the site was isolated after a paired labeling procedure as follows. One portion of the antibody was iodinated with 125I-labeled hypoiodite. A second portion was iodinated with 131I-labeled hypoiodite in the presence of hapten to protect the site from iodination. The protected and unprotected preparations were mixed, digested with pepsin and the iodinated peptides separated. The ratio of 125I:131I relative to that of the unfractionated digest was determined for the peptides; a high ratio indicated that the peptide was derived from the antibody site. A high-ratio peptide, equivalent to at least 37% of the total antibody sites present, had the sequence Ile-DIT-Asp. The peptide was shown to be derived from the heavy chain of the antibody and was probably from the variable portion.

[学科分类] 生物科学（综合）