Prostaglandin H synthase-dependent mutagenic activation of benzidine in a Salmonella typhimurium Ames tester strain possessing elevated N-acetyltransferase levels.

Watanabe and colleagues (Biochem. Biophys. Res. Commun. 147: 974-979, 1987) have constructed plasmid-containing derivatives of Salmonella typhimurium Ames tester strain TA1538 with high levels of acetyltransferase activities. In this paper, we describe the mutagenic response of one of these strains, TA1538/1,8-DNP6 (pYG 121), to the bladder carcinogen benzidine and other arylamines. Strain TA1538/1,8-DNP6 (pYG 121) was far more sensitive to benzidine than any previous tester strain, following metabolism of the aromatic amine by hamster hepatic S9, ram seminal vesicle microsomal preparation (RSVM), or purified prostaglandin synthase. Therefore, bacterial acetyltransferase-dependent metabolism of a proximate mutagen is implicated in each of these systems. The mechanism of RSVM-dependent activation of benzidine was examined further. The arachidonic acid-independence and indomethacin insensitivity previously noted with strain TA98 were also observed with the new tester strain. We confirmed that prostaglandin H synthase is the enzyme activity responsible for activation of benzidine by RSVM. Purified prostaglandin H synthase holoenzyme, or apoenzyme reconstituted with heme, supported benzidine activation. However, apoenzyme reconstituted with manganese protoporphyrin IX, which yields enzyme having cyclooxygenase activity but not peroxidase activity, was inactive. Addition of catalase inhibited, and addition of exogenous hydrogen peroxide increased, RSVM-mediated benzidine mutagenicity. We propose that hydrogen peroxide released by the tester strain bacteria (rather than arachidonic acid-derived peroxide) is the oxidizing agent which supports prostaglandin H synthase peroxidase activity in Ames test systems.