Activity coupling and complex formation between bacterial luciferase and flavin reductases

Luminous bacteria contain several species of flavin reductases, which catalyze the reduction of FMN using NADH and/or NADPH as a reductant. The reduced FMN (i.e. FMNH2) so generated is utilized along with a long-chain aliphatic aldehyde and molecular oxygen by luciferase as substrates for the bioluminescence reaction. In this report, the general properties of luciferases and reductases from luminous bacteria are briefly summarized. Earlier and more recent studies demonstrating the direct transfer of FMNH2 from reductases to luciferase are surveyed. Using reductases and luciferases from Vibrio harveyi and Vibrio fischeri, two mechanisms were uncovered for the direct transfer of reduced flavin cofactor and reduced flavin product of reductase to luciferase. A complex of an NADPH-specific reductase (FRPVh) and luciferase from V. harveyi has been detected in vitro and in vivo. Both constituent enzymes in such a complex are catalytically active. The reduction of FRPVh-bound FMN cofactor by NADPH is reversible, allowing the cellular contents of NADP(+) and NADPH as a factor for the regulation of the production of FMNH2 by FRPVh for luciferase bioluminescence. Other regulations of the activity coupling between reductase and luciferase are also discussed.