Styrene monooxygenase which catalyzes the first step in the aerobic styrene degradation pathway by enantioselective epoxidation of the vinyl side chain. In a two-component system, StyB reductase utilizes NADH to reduce FAD, which is then transferred to the oxygenase; the electron transfer is proposed to occur via a diffusing flavin. FADH2 + O2 + styrene = (2S)-2-phenyloxirane + FAD + H(+) + H2O Aromatic compound metabolism. Homodimer. A direct interaction with the monooxygenase reductase component StyB seems not to be necessary for the enzymatic activity (By similarity). Belongs to the StyA family.