Superoxide anion reacts with enzyme intermediate in the bacterial luciferase reaction competitive with intramolecular electron transfer.

Addition of KO2 in dimethyl sulfoxide (DMSO) to the in vitro bacterial luciferase reaction subsequent to its initiation resulted in a biphasic decay of light emission. The first and more rapid phase is attributed to quenching by DMSO. With DMSO alone the continuing decay is kinetically the same as in a control reaction. With KO2 added the second decay phase is more rapid and dependent on the KO2 concentration. The enhanced decay is attributed to superoxide anion generated from KO2 reacting without light emission with an enzyme peroxy intermediate, breaking down of the peroxide bond through intermolecular electron transfer from the superoxide anion, in competition with an intramolecular electron transfer from the N(5) position of the flavin ring, which normally leads to the production of the excited luciferase-dihydroflavin-4a-hydroxide.