Fig. 1.

Oxygen Dilemma of P450 monooxygenase reactions. As NAD(P)H cannot directly reduce the (Fe-containing) monooxygenases’ active sites redox mediators are necessary to transform the (NAD(P)H-dependent) hydride transfer into two successive single electron transfer steps. The reduced mediators (radicals) however also react spontaneously with dissolved O₂ eventually yielding H₂O₂. This results in a futile uncoupling of the regeneration reaction from the monooxygenation reaction.