Steady-state kinetic analysis of halogenase-supporting flavin reductases BorF and AbeF reveals different kinetic mechanisms.

The short-chain flavin reductases BorF and AbeF reduce FAD to FADH, which is then used by flavin-dependent halogenases (BorH and AbeH respectively) to regioselectively chlorinate tryptophan in the biosynthesis of indolotryptoline natural products. Recombinant AbeF and BorF were overexpressed and purified as homodimers from E. coli, and copurified with substoichiometric amounts of FAD, which could be easily removed.