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A new approach to measurement of redox-cycling activity in Escherichia coli.

Redox-cycling agents catalyze the flow of reducing equivalents to oxygen; this process generates superoxide ion and other reduced oxygen species. Measurements of redox-cycling activity have been performed previously by studying cyanide-resistant oxygen consumption (respiration) of Escherichia coli cells. E. coli strain GK100, lacking both terminal oxidases, has almost no measurable respiration. We show that the use of this strain eliminates the requirement for cyanide in measurements of redox-cycling activity. The addition of either menadione sodium bisulfite or plumbagin, well-known redox-cycling agents, to GK100 cells resulted in high levels of oxygen consumption. The rate of menadione bisulfite-induced oxygen consumption in this respiration-deficient strain, in the absence of cyanide, was comparable to the cyanide-resistant respiration of isogenic respiration-proficient E. coli strains. In GK100 cells, cyanide increased menadione bisulfite-induced oxygen consumption but had no effect on plumbagin-induced oxygen consumption.