Figure 10.

Proposed redox catalytic cycle of carnitine monooxygenase. A redox catalytic cycle for carnitine monooxygenase was proposed based on the experimentally characterized redox states of the present study. Reduction of CntB by the two-electron donor NADH results in the FMNH*/[2Fe-2S]⁺ state (I). Subsequent two-electron transfer onto CntA reveals the electron donor in the CntB FMN/[2Fe-2S]²⁺ state (II) and activates the electron acceptor in the CntA [2Fe-2S]⁺/[Fe]²⁺ (III). Subsequent electron transfer onto O₂ results in the CntA [2Fe-2S]²⁺/[Fe]²⁺ redox state, which resembles the as-purified state of this protein (IV) (compare to Fig. 7B). The reduction of O₂ then leads to the formation of the monooxygenated l-carnitine product (not shown) (compare to Fig. 2A) and H₂O. Cleavage of the C–N bond of the intermediate then results in the formation of malic semialdehyde and TMA.