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 O(2⨪) 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 O(2⨪), in a radical–radical addition, to yield an unstable dioxetane, whose decomposition yields light. Superoxide dismutases (SOD), by decreasing [O(2⨪)], inhibit light production and to the same degree inhibit other O(2⨪)-dependent reactions in the cell. Lucigenin luminescence was used to show that the levels of SOD in the parental strain provide ≈95% protection of all O(2⨪)-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.