Conversion of liposomal 4-androsten-3,17-dione by A. simplex immobilized cells in calcium pectate

Arthrobacter simplex ATCC 6946 free and immobilized cells were assayed for their ability to convert 4-androsten-3,17-dione (AD) to 1,4-androstadien-3,17-dione (ADD) in aqueous and liposomal media. Bioconversions were carried out in a 100 ml flask containing 25 ml of AD liposomal or aqueous medium for 3h, and AD concentrations ranging from 0.3 to 1.0 mM were tested. AD/ADD ratios in samples were determined by HPLC. Biotransformation of substrate entrapped in multilamellar vesicles (MLV) was demonstrated to be better than the corresponding free form. In the former case, 2h were necessary to completely bioconvert 1 mM AD. By contrast, 3h were needed to reach 50% bioconversion in (4%) ethanol medium containing 0.63 mM AD. The liposomal medium allows us to perform steroid conversions at high concentrations of AD, reusing immobilized cells in suitable conditions which are non-toxic for microorganisms.