A combined enzyme system, consisting of hydrogenase, lipoamide dehydrogenase and 20β-hydroxysteroid dehydrogenase has been enclosed in reversed micelles. This system catalyzes the stereo- and site-specific enzymatic reduction of apolar, poorly water-soluble ketosteroids to their corresponding 20β-hydroxyform using an in situ NADH-regenerating enzyme system and H2 as ultimate reductant.
