The oxidation of 2-aminofluorene by prostaglandin endoperoxide synthetase. Comparison with other peroxidases.

Abstract

We have examined the prostaglandin endoperoxide synthetase-dependent metabolism of the arylamine carcinogen 2-aminofluorene (2-AF). Ram seminal vesicle microsomes fortified with arachidonic acid metabolize 2-AF to products covalently bound to microsomal macromolecules, water-soluble metabolites, and two organic extractable metabolites. The organic extractable metabolites were identified by co-chromatography, uv-visible spectrophotometry, and mass spectrometry as 2-nitrofluorene and 2,2'-azobisfluorene (azofluorene). Hydrogen peroxide also supports 2-AF metabolism to the same products, suggesting that the hydroperoxidase activity of prostaglandin endoperoxide synthetase is responsible for the co-oxidation. The highly reactive oxygenated metabolites of 2-AF, N-hydroxy-2-AF, and 2-nitrosofluorene, are metabolized by prostaglandin endoperoxide synthetase to one major product, 2-nitrofluorene. The metabolism of 2-AF, N-hydroxy-2-AF, and 2-nitrosofluorene is extremely rapid, reaching completion in less than 30 s. The horseradish peroxidase/H2O2 system also metabolites 2-AF to 2-nitrofluorene and azofluorene. The chloroperoxidase/H2O2 system, however, yields primarily 2-nitrosofluorene from 2-AF. These results suggest that 2-AF is oxidized to an electrophilic intermediate(s) by prostaglandin endoperoxide synthetase, which either binds covalently to tissue macromolecules or is further rapidly oxidized to 2-nitrofluorene and azofluorene. Furthermore, this reaction probably proceeds through a free radical mechanism similar to that of horseradish peroxidase.