ACTIVATION OF 4-NITRO-O-PHENYLENEDIAMINE BY THE S2 FRACTION OF ZEA-MAYS TO MUTAGENIC PRODUCT(S)

Studies on plant metabolic activation with the S2 fraction from Zea ma ys have been developed. The 4-nitro-o-phenylenediamine (NOP) activatio n by S2 has been analyzed with the Ames test as a short-term assay. Th e NOP mutagenic potency was increased two-fold by S2, while rat liver S9 produced the contrary effect. The presence of a NADPH-generating sy stem and the treatment of S2 with CO do not modify S2 activation of NO P. In this fraction, neither cytochrome P450 nor some enzymatic activi ties depending on cyt-P450 (aniline hydroxylase and aminopyrine demeth ylase) were detected. Therefore, the enhancement of NOP mutagenic pote ncy by S2 is independent of the mixed-function oxidase system. On the other hand, inhibitors of the peroxidase activity such as N-acetyl-p-a minophenol caused a partial inhibition of S2 activation of NOP. Likewi se, diethyldithiocarbamate produced both a reduction of the S2 peroxid ase activity in biochemical assays and a partial inhibition of S2 acti vation of NOP. Moreover, it was possible to find a direct correlation between the activity of peroxidase per plate of both the S2 fraction a nd horseradish peroxidase and the number of revertants induced by NOP in the TA98 strain. On the basis of these results, we report that a HR P-like peroxidase activity must be the main pathway of NOP activation by the plant metabolic activation system studied in this work.