Reducing substrate activity of some aromatic amines for prostaglandin H synthase

The ability of eight different aromatic amines to serve as reducing substrates for the conversion of 5-phenyl-4-pentenyl-hydroperoxide to 5-phenyl-4-pentenylalcohol by prostaglandin H synthase (PHS) was studied. The methodology used a direct assay for the reduction of hydroperoxide to alcohol and allowed an assessment of the reducing substrates' efficiency as a donor of electrons to the peroxidase component of highly purified PHS. The eight amines tested include, 1-naphthylamine, 2-naphthylamine, 2,4-diaminoanisole, 2,5-diaminoanisole, 2-aminofluorene, 2-acetylaminofluorene, 2-amino-anthracene and benzidine. The compounds tested were either very efficient substrates or showed minimal activity as reducing substrates. Benzidine, 2,4-diaminoanisole and 2,5-diaminoanisole were excellent substrates providing nearly stoichiometric hydroperoxide reduction even at low enzyme concentrations. On the other hand, the five remaining compounds showed no activity as reducing substrates. Increases in enzyme and/or substrate concentration still did not produce any significant enzymatic activity with the poor substrates. The results of these investigations provide important information concerning the metabolic activation of these aromatic amines by PHS. There is evidence in the literature that some of these amines are metabolized by PHS to mutagenic and carcinogenic species. For the efficient reducing substrates this remains a reasonable suggestion. However, for the poor reducing substrates, alternative possibilities for the oxidizing agent must be considered.