Regioselective reduction of a steroid in a reversed micellar system with enzymatic NADH-regeneration

The regioselective reduction of androstandione to androsterone by 3α-hydroxysteroid dehydrogenase (HSDH) from Pseudomonas testosteroni was coupled to a cofactor (NADH) regeneration system with the oxidation of ethanol by yeast alcohol dehydrogenase (YADH) in sodium dioctyl sulfosuccinate (AOT)/isooctane reversed micelles. Each reaction was dominated by the system's water content (W₀ = [H₂O]/[AOT]). The catalytic activity of YADH increased monotonically with W₀, whereas HSDH showed bell-shaped dependency on W₀. Using a reversed micellar system increased stability of both enzymes in comparison with an aqueous system and prolonged NADH-regeneration; namely, a seven-fold increase in the total turnover number of NADH was achieved. These results suggest that the reversed micellar system is a promising choice for conjugate enzymatic reactions with dehydrogenases in a nonaqueous media.