The role of hydrogen peroxide produced by polychlorinated biphenyls in PMR1-deficient yeast cells.

Polychlorinated biphenyls (PCBs) are well-known recalcitrant environmental pollutants. Although the metabolism of the PCBs has been intensively studied, very little is known about their mechanism of toxicity in living organisms or how they are degraded. We have examined the effects of PCBs on two different yeast strains to determine their mechanism of action. One yeast strain (K601, wild type) is resistant to the growth-inhibitory effect of PCBs, whereas the other strain (AA542, PMR1 mutant) is susceptible. PCBs increased the level of intracellular hydrogen peroxide in AA542 cells but not in K601 cells. In the presence of alpha-tocopherol or ursolic acid the growth of AA542 cells was not inhibited by treatment with PCBs. These results suggest that PCBs block cell growth through production of hydrogen peroxide in the PMR1 mutant strain, AA542. We compared superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase activities in both strains. The catalase activity in K601 cells was 10 times higher than that in AA542 cells. In contrast, there was no difference in activities of SOD and GPx between the two strains. Collectively, these observations indicate that oxidative stress causes the inhibition of cell growth observed in catalase-deficient yeast cells exposed to PCBs.