Figure 7.

Proposed mechanism for two-component flavin-dependent alkanesulfonate monooxygenases based on the Ternary-MsuD structure. Dioxygen is colored red, and R can be a hydrogen or larger alkyl chain. The proton donor AH is likely a water molecule. Alternatively, hydroxymethanesulfonic acid may nonenzymatically convert to sulfite and aldehyde. Positioning of MS⁻ is consistent with oxygenation at the methyl, with both the N5- and C4a-pathways included for comparison. Reduced flavin is generated by the NADH:FMN oxidoreductase MsuE (not depicted).