Abstract
In this study, we investigated the stereospecificity of hydride transfer from NADH to flavin mononucleotide (FMN) in reactions catalyzed by the FMN-dependent NADH-indigo reductase expressed by thermophilic Bacillus smithii. We performed (1) H-NMR spectroscopy using deuterium-labeled NADH (4R-(2) H-NADH) and molecular docking simulations to reveal that the pro-S hydrogen at the C4 position of the nicotinamide moiety in NADH was specifically transferred to the flavin-N5 atom of FNM. Altogether, our findings may aid in the improvement of the indigo dyeing (Aizome) process.