Hydroxylation of Steroids by Immobilized Microbial Cells

Abstract

It is well known that many fungi hydroxylate steroids and other compounds at specific position(s). Immobilized fungi will be useful as biocatalysts for such hydroxylation processes. However, the mycelial cells of fungi are fragile; and the complex hydroxylation systems may lose activity during immobilization. These facts make the immobilization of active and vegetative mycelia difficult. Recently, Ohlson et al. (1) described steroid hydroxylation using mycelial cells of Curvularia lunata, which were derived from the spores entrapped in calcium alginate gels; however, the hydroxylation activity of the immobilized cells was somewhat unstable. We have developed novel and convenient methods to immobilize enzymes, microbial cells, and organelles using photo-crosslinkable resin prepolymers and water-miscible urethane prepolymers (2, 3). These methods can be applied to the entrapment of living fungal spores because of the mildness of the procedures. Spores of C. lunata were entrapped in various gels, and incubated for 60 hr to form mycelia in potato-dextrose broth containing Reichstein’s Substance S (RSS) as inducer. The immobilized fungal mycelia thus obtained were used to hydroxylate RSS at the 11β-position to yield hydrocortisone in a reaction medium containing 2.5% dimethyl sulfoxide (4).