Regulation of the synthesis of superoxide dismutase in Escherichia coli. Induction by methyl viologen.

Abstract

Paraquat (methyl viologen) caused a rapid and pronounced increase in the rate of biosynthesis of the manganese-containing superoxide dismutase, in E’scherichia coli B growing aerobically, in a trypticase soy-yeast extract (TSY) medium. Removal of the paraquat was followed, after a lag of 30 min, by a marked decrease in cellular content of this enzymic activity. Paraquat also caused a moderate induction of catalase but had little effect on peroxidase or on the iron-containing superoxide dismutase. The concentrations of paraquat, which were effective in inducing the manganese-superoxide dismutase, exerted little effect on the growth rate and no effect on the net rate of respiration, but did increase that fraction of the total oxygen consumption which was insensitive to 1.0 mu cyanide. Cells whose content of manganese-superoxide dismutase had been augmented by paraquat induction, exhibited increased resistance towards oxygen toxicity and towards the oxygen enhancement of the lethality of streptonigrin. It seems likely that paraquat subverts a portion of the normal, cyanide-sensitive, electron flow in the cells and transfers that electron flow to oxygen, in a univalent and cyanide-insensitive manner. This results in an increased rate of intracellular production of O,-. 02-, or some product uniquely derived from 02-, then induces or derepresses the biosynthesis of the manganese-superoxide dismutase, which defends the cell against the deleterious reactivities of this radical.