Abstract
An intensive and systematic investigation of the oxidation of cholesterol (CL) to cholest-4-en-3-one (CN) by Rhodococcus erythropolis was undertaken in the presence of natural and chemically modified cyclodextrins (CDs) in a stirred bioreactor. The biotransformation was found to be strongly affected by the mode of addition of the natural CDs. While simultaneous addition of CL with either β- or λ-CD led to a limited enhancement effect, the microbial oxidation of β- and λ-CD complexes of CL was totally inhibited. In contrast, the alkylated CDs- dimethyl-, trimethyl- and hydroxypropyl-β-CD exhibited a remarkable enhancement of the microbial oxidation, irrespective of their mode of addition. The performance of the alkylated CDs was interpreted in the light of the measured phase solubility diagrams of CL and CN. It was thus shown that unlike the low solubilising power of hydroxypropyl-β-CD, dimethyl- and trimethyl-β-CD at 90 mm each, dissolved 9.3 and 8.7 g/l of CL and CN, respectively. Further investigation focused on the formation of CD complexes with CL and CN, analysed by X-ray powder diffractometry, differential scanning calorimetry and 1H-nuclear magnetic resonance. It was thus shown that β-CD forms a 2:1 CD:CL and CD:CN water-insoluble complexes. A mechanism of the biotransformation in homogeneous and heterogeneous CD media was presented while suggesting a direct interaction of the CD-substrate complex with microbial cells.
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Jadoun, J., Bar, R. Microbial transformations in a cyclodextrin medium. Part 3. Cholesterol oxidation by Rhodococcus erythropolis . Appl Microbiol Biotechnol 40, 230–240 (1993). https://doi.org/10.1007/BF00170372
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DOI: https://doi.org/10.1007/BF00170372