Bioluminescence emission from the reaction of luciferase-flavin mononucleotide radical with O2-..

The blue neutral luciferase flavin radical has been shown not to be in a catalytically significant equilibrium with species leading to emission of light [Kurfürst, M., Ghisla, S., Presswood, R., & Hastings, J. W. (1982) Eur. J. Biochem. 123, 355-361]. It is shown here that this radical can nevertheless react with O2-. to form a species that is competent in light emission. From its properties, the species formed is deduced to be luciferase-FMNH 4a-hydroperoxide, a key intermediate in the normal luciferase reaction. Although it is concluded that this intermediate can undergo a reversible homolytic dissociation to yield free superoxide and the corresponding luciferase radical, the slowness of these steps precludes a catalytic significance for these pathways in the normal bioluminescent reaction.