Prostaglandin H synthase-catalyzed ring oxygenation of 2-naphthylamine: evidence for two distinct oxidation pathways.

Previous studies showed that prostaglandin H synthase (PHS) cooxidizes 2-naphthylamine (2-NA) to ring-oxygenated products. These metabolites are atypical for a peroxidase-mediated reaction and are completely different from the polymeric nonoxygenated metabolites of 2-NA that are generated with the model peroxidase horseradish peroxidase (HRP). In this study, we investigated possible explanations for the PHS-catalyzed formation of ring-oxygenated 2-NA metabolites. We found that introduction of a peroxyl radical-generated cosubstrate into the HRP/2-NA system resulted in the formation of the same ring-oxygenated products observed in the PHS/2-NA system. 18O2 incorporation studies were utilized to further characterize the source of oxygen in the ring-oxygenated 2-NA metabolites. The data show that, in the case of PHS, ring oxygenation can occur both by peroxyl radical-mediated attack on 2-NA and by direct transfer of peroxide oxygen from PHS to 2-NA.