The long range goal of this project is to study the oxidation of chemicals to toxic or carcinogenic metabolites by prostaglandin H synthase (PHS) and to demonstrate the importance of this enzyme system in chemical-induced toxicity or carcinogenesis. We have shown that aromatic amine carcinogens, are metabolized to mutagens by PHS. PHS dependent oxidation occurred by a free radical mechanism and resulted in the formation of DNA adducts which can be used as in vivo markers for PHS-dependent oxidation. We have further studied the formation of amine mutagens by PHS using bacterial tester systems having different levels of acetylation activity. Using the bladder carcinogen as a model we showed that the amine is first acetylated to acetylbenzidine. PHS but not HRP then metabolizes the acetylbenzidine to nitroacetylbenzidine. The nitro metabolite is a potent direct acting mutagen. This explains the role of bacterial acetylation and the difference between PHS and HRP. Our data suggest that PHS is a versatile enzyme system that can catalyze a variety of reactions which are important in the conversion of chemicals to carcinogenic metabolites in extra hepatic tissue. We have also investigated the mechanisms involved in the oxidation of arachidonic acid to PGG(2)/PGH(2). We obtained data that indicates that the cyclooxygenase and peroxidase activity are closely linked in that the produce of the cyclooxygenase, PGG(2), is the preferred substrate for the peroxidase. We have also investigated the tyrosyl radical intermediates of PHS that are the proposed catalatic intermediate. Our data indicate that the tyrosyl radical is the result of or involved in the inactivation of PHS and not a catalatic intermediate.
