The effect of paraquat on the mutagenicity of benzo(a)pyrene

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Abstract
Elevated activities of superoxide dismutase (SOD) were detected in histidine‐requiring strains of Salmonella typhimurium after the bacteria were preincubated for 1 h at 37°C with S‐9 mix and paraquat (methylviologen, PQ2+) at 10−4M. A fivefold increase in SOD level was found for strains TA 98 and TA 100. These elevated levels of SOD activity were correlated with a significant reduction of the mutagenicity of metabolically activated benzo(a)pyrene (B(a)P) in these tester bacteria when evaluated in a preincubation assay system. A 69.0–92.5% and 23.5–66.9% reduction was noticed when 0.5–4.0 μg per plate of B(a)P was used in TA 98 and TA 100, respectively. However, exogenous superoxide dismutase at 10–100 μg ml−1 added to top agar had no significant effect on the number of revertants produced by activated B(a)P. These data indicate a major role of intracellular superoxide anion in promoting mutagenicity of B(a)P.

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