Bioconversion of lipophilic compounds in non-aqueous solvent. Effect of gel hydrophobicity on diverse conversions of testosterone by gel-entrapped Nocardia rhodocrous cells

Abstract

The bioconversion of testosterone (TS) in water-saturated benzene-n-heptane (4:1 by volume) was mediated by Nocardia rhodocrous cells whose steroid Δ1-dehydrogenase and 17β-hydroxysteroid dehydrogenase were induced by TS. TS was transformed into 4-androstene-3,17-dione (4-AD), dehydrotestosterone (DTS) and 1,4-androstadiene-3, 17-dione (ADD) by incubating with the cell suspensions in the presence of phenazine methosulfate (PMS). Time-courses of TS transformation revealed that DTS and 4-AD were produced initially and further oxidized to ADD. Thus, the final product, ADD; was formed via two different pathways: TS→4-AD→ADD and TS→DTS→ADD. In these routes, Δ1-dehydrogenation required PMS, while 17β-dehydrogenation could proceed without any exogenous electron acceptor. N. rhodocrous cells entrapped in hydrophilic gels (H-gel) and lipophilic gels (L-gel) prepared by photo-crosslinkable resin prepolymers and urethane prepolymers were useful for effective dehydrogenations of TS. The cells entrapped in L-gels produced 4-AD as the major product, whereas DTS was the main product by the cells in H-gel. The difference in the profiles of dehydrogenation products can be explained by low affinity of PMS for L-gel-entrapped cells and of TS for H-gel-entrapped cells. Inhibitory effect of DTS on 17β-hydroxysteroid dehydrogenase also would be responsible for the accumulation of DTS in the latter case. Thus, different routes for product formation could be selected by using resin prepolymers of appropriate hydrophilicity or hydrophobicity for entrapment of biocatalysts.