The steroid monooxygenase from Rhodococcus rhodochrous; a versatile biocatalyst

The substrate scope of a steroid monooxygenase (STMO) from Rhodococcus rhodochrous DSM 43269 was investigated for a large range of different ketone substrates. These studies revealed that this enzyme not only oxygenates steroids, but also ketone moieties of a series of other open-chain ketones, such as cyclohexyl methyl ketone, cyclopentyl methyl ketone, and 3-acetylindole. Furthermore, the STMO catalyzed the oxygenation of cyclobutanone derivatives. Comparative biotransformations with recombinant Escherichia coli resting cells harboring the STMO, the cycloalkanone monooxygenase (CAMO) from Cylindrocarpon radicicola or the cyclohexanone monooxygenase (CHMO) from Acinetobacter calcoaceticus revealed that the STMO is enantiodivergent compared to the CHMO-type. Moreover, the STMO resulted in a higher enantiomeric excess of the product lactones compared to the known BVMOs of the same enantiopreference, such as cyclopentanone monooxygenases.