Benzidine binding to nucleic acids mediated by the peroxidative activity of prostaglandin endoperoxide synthetase

The cooxidative metabolism of the urinary bladder carcinogen benzidine was examined using renal inner medullary microsomes. The products of [14C]benzidine metabolism were recovered in the aqueous but not in the organic soluble fraction of reacting mixtures. The reactive metabolites formed during cooxidative metabolism of benzidine bound to DNA and transfer RNA. Cooxidative metabolism of benzidine and subsequent binding to nucleic acids was dependent upon specific fatty acid substrates and was blocked by inhibitors of prostaglandin endoperoxide synthetase. The ratio of the rates of benzidine product formation was approximately 10:3:1 (trichloroacetic acid precipitable:non-trichloroacetic acid precipitable:transfer RNA bound) over a wide range of arachidonic acid concentrations. Cumene hydroperoxide also initiated cooxidative metabolism of benzidine but was less effective than was arachidonic acid. In contrast to arachidonic acid, cumene hydroperoxide-mediated metabolism of benzidine and fuaiacol peroxidase activity was not blocked by indomethacin. Using electron paramagnetic resonance, radicals were detected after addition of arachidonic acid or cumene hydroperoxide to the microsomal preparation. Radical production was completely quenched by addition of benzidine or guaiacol. These results demonstrate that the peroxidative activity of renal medullary prostaglandin endoperoxide synthetase mediates benzidine metabolism and subsequent binding to nucleic acids.