In order to demonstrate the O2 tolerance of the SH for flavin regeneration and the extension to the FAD cofactor, we used our system to drive the epoxidation of styrenes catalyzed by the styrene monooxygenase from Pseudomonas sp. VLB120. Styrene monooxygenase is a twocomponent, diffusible flavin monooxygenase composed of StyA, the FADH2-dependent monooxygenase subunit and StyB (a flavin reductase catalyzing the in situ generation of FADH2 from FAD and NADH). The FADH2 regeneration system proposed here allowed to circumvent