StyA SH FAD 200 333 3.3 Reaction conditions: 1 ml of KPi buffer pH 7.5 containing 300 µM FAD, 5 mM substrate. The gas mixture was 10% O2 30% N2 and 60% H2. SH (3 µM) and styrene monooxygenase (5 µM) was added to start the reaction. The reaction was performed at 30 °C for 16 hours. Conversions and ee values were determined by GC-FID analysis. SH = NAD + -reducing hydrogenase, StyA = styrene monooxygenase; a Total turnover numbers of mol styrene epoxide per mol enzyme or cofactor the nicotinamide cofactor together with the reductase subunit (StyB). Up to 1 mM of enantiopure (S)-styrene oxide was obtained upon incubation of StyA with SH and FAD under O2/H2 atmosphere for the reduction of styrene with the co-substrate O2 (Scheme 1). The TTN of SH for FAD reduction was up to 333.