IN-VITRO FORMATION AND DEGRADATION OF 2-AMINO-1-METHYL-6-PHENYLIMIDAZO[4,5-B]PYRIDINE (PHIP) PROTEIN ADDUCTS

Adduct formation between the food mutagen 2-amino-1-methyl-6-phenylimi dazo[4,5-b]pyridine (PhIP) and rat serum albumin (RSA) was studied in vitro using hepatic microsomes isolated from polychlorinated biphenyl- induced rats. With 1-methyl-2-nitro-6-phenylimidazo[4,5-b]pyridine (2- nitro-PhIP) as starting material, four main products were formed. Pret reatment of RSA with beta-mercaptoethanol markedly increased the yield of one of them. In this adduct, the C-2 of PhIP was linked to cystein e of RSA at position 34 in a C-S linkage. With N-2-acetoxy-PhIP as sta rting material, unstable conjugates were formed with RSA as well as wi th glutathione (GSH) and cysteine. The suggested structures of the GSH and cysteine conjugates, GSH-S-N-2-PhIP and cysteine-S-N-2-PhIP respe ctively, are based on mass spectra and UV spectra. The degradation of the conjugates of GSH and cysteine as well as of the protein adduct we re monitored. They all resulted in the same degradation product, ident ified as 2-amino-5 hydroxy-1-methyl-6-phenylimidazo[4,5-b]pyridine (5- hydroxy-PhIP).