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 competiton 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. © 1997 John Wiley & Sons, Ltd.