In vitro enhancement of the mutagenicity of 4‐nitro‐o‐phenylenediamine by plant S‐9

The direct‐acting mutagen 4‐nitro‐o‐phenylenediamine (NOP) was activated in vitro by pea or tobacco S‐9 into a more potent mutagen in Salmonella typhimurium strain TA98. NOP mutagenicity was not altered by Aroclor 1254‐induced rat liver S‐9. The plant S‐9 activation of NOP was heat‐sensitive but was not NADPH‐dependent, did not involve superoxide radicals, and was not inhibited by CO. A direct relationship between plant peroxidase and NOP activation was established. Several purified peroxidases including horseradish peroxidase, chloroperoxidase, and lactoperoxidase also activated NOP. The perodoxidative process was not H₂O₂‐dependent but was partially inhibited by a peroxidase inhibitor.