Lucigenin luminescence as a measure of intracellular superoxide dismutase activity in Escherichia coli.

Lucigenin and paraquat are similar in that each can be taken into Escherichia coli and can then mediate O2.- production by cycles of univalent reduction, to the corresponding monocation radical, followed by autoxidation. Thus, both compounds caused induction of enzymes that are regulated by the soxRS regulon. The lucigenin cation radical has the added property of reacting with O2.-, in a radical-radical addition, to yield an unstable dioxetane, whose decomposition yields light. Superoxide dismutases (SOD), by decreasing [O2.-], inhibit light production and to the same degree inhibit other O2.(-)-dependent reactions in the cell. Lucigenin luminescence was used to show that the levels of SOD in the parental strain provide approximately 95% protection of all O2.(-)-sensitive targets in E. coli. This degree of protection was so close to the limit of 100% that halving the parental level of [SOD], or increasing it 5-fold, had only marginal effects on the intensity of lucigenin-dependent luminescence.