Identification of the major serum albumin adduct formed by 4-aminobiphenyl in vivo in rats.

Serum albumin was isolated from rats at 27 h after administration of the carcinogen [2,2'-3H]-4-aminobiphenyl. Pronase digestion of the purified albumin yielded a mixture of radiolabeled materials which was resolved into 5 major components by reverse-phase liquid chromatography. From detailed UV, 1H-NMR, and mass spectral analyses, four of these were determined to be 4-aminobiphenyl, 4'-hydroxy-4-acetylaminobiphenyl, and two other metabolites, all of which are presumed to be non-covalently associated with the serum albumin. The fifth component, however, resulted from covalent bond formation and was identified as a tetrapeptide containing 3-tryptophanyl-4-acetylaminobiphenyl, the amino acid sequence of which was H2N-ala-trp-ala-val. Since rat serum albumin contains only a single tryptophan residue in a hydrophobic drug binding site, its high selectivity for carcinogen binding suggests a unique role for this protein in the detoxification and/or transport of ultimate carcinogenic metabolites.