Fig. 5: Mutational and spectral analyses and the proposed VibO mechanism.

a The relative enzyme activities for wild-type (WT) and variants of VibO incubated with 6. The columns represent accumulation of 3 or 7 or none of them (in blank); the highest mean value was set 100%; bars indicate ± SD of three replicates. b Reductive reaction of VibO with NADPH (0 to 4 mM) in the absence of substrate 6. The gray dash denotes the purified VibO. Spectral responses were collected immediately after adding NADPH in a cuvette. c Time-course spectral analysis of VibO with NADPH (50 μM) in the absence of 6 (Supplementary Fig. 36). The level of NADPH and FAD over time was monitored at 340 nm and 450 nm/460 nm, respectively. d Suggested peroxyflavin (FAD-C4a-O-O^‒)-involving Baeyer-Villiger oxidation of 6 to the oxepinone 3. Deuterium incorporation is shown in blue. e Hydroxylation of 6 to 7 via the presumed dienone form 7′, referring to the mechanism of PHHY^35,38. Source data for a, b, and c are provided as a Source Data file.