Microbial transformations in a cyclodextrin medium. Part 2. Reduction of androstenedione to testosterone by Saccharomyces cerevisiae

An intensive and systematic investigation of the reductive transformation of androstenedione (AD) to testosterone by Saccharomyces cerevisiae was undertaken in the presence of natural and chemically modified cyclodextrins (CD). The bioconversion was significantly larger in the presence of beta - and gamma -CD and hydroxypropyl- beta -CD but only slight in the presence of alpha -CD and dimethyl- and trimethyl- beta -CD. The performance of the various cyclodextrin media was interpreted in the light of the measured phase solubility diagrams of AD. Further investigation focused on biotransformation of the beta -CD-androstenedione complex, the formation of which was studied by differential scanning calorimetry and X-ray powder diffractometry and stoichiometry determined by super(1)H-nuclear magnetic resonance. A mechanism whereby CDs reduce the effective inhibitory concentrations of substrate and product as well as facilitate transport of the complexed substrate though the yeast cell wall has been suggested for the CD-promoted biotransformation.