Scheme 4.

Simplified molecular architecture of multicomponent monooxygenases that are not directly dependent on NAD(P)H. Blue: path of reducing equivalents. NAD(P)H serves as a general reductant, transferring its reducing equivalents to a mediator molecule (either a flavin or an iron–sulfur cluster protein) with catalysis by a reductase. The usually protein‐based mediator delivers the reducing equivalents to the monooxygenase subunit for productive oxygen activation. However, direct reaction of the reduced mediator with O₂ leads to futile reoxidation and (eventually) H₂O₂ formation.