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Applied and Environmental Microbiology, May 2009, p. 3062-3068, Vol. 75, No. 10
0099-2240/09/$08.00+0     doi:10.1128/AEM.02058-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Stereospecific Biotransformation of Dihydrodaidzein into (3S)-Equol by the Human Intestinal Bacterium Eggerthella Strain Julong 732{triangledown}

Mihyang Kim,1 Su-Il Kim,1 Jaehong Han,2 Xiu-Ling Wang,3 Dae-Geun Song,4 and Soo-Un Kim1,5*

Department of Agricultural Biotechnology and Research Institute for Agriculture and Life Sciences, Seoul National University, Seoul 151-921, South Korea,1 Metalloenzyme Research Group and Department of Biotechnology, Chung-Ang University, Anseong 456-756, South Korea,2 College of Life Science, Agricultural University of Hebei, Baoding 071001, China,3 Natural Products Research Center, Korea Institute of Science and Technology Gangneung Institute, Gangneung 210-340, South Korea,4 Plant Metabolism Research Center, Kyung Hee University, Yongin 446-701, South Korea5

Received 5 September 2008/ Accepted 10 March 2009

Stereochemical course of isoflavanone dihydrodaidzein (DHD) reduction into the isoflavan (3S)-equol via tetrahydrodaidzein (THD) by the human intestinal anaerobic bacterium Eggerthella strain Julong 732 was studied. THD was synthesized by catalytic hydrogenation, and each stereoisomer was separated by chiral high-performance liquid chromatography. Circular dichroism spectroscopy was used to elucidate the absolute configurations of four synthetic THD stereoisomers. Rapid racemization of DHD catalyzed by Julong 732 prevented the substrate stereospecificity in the conversion of DHD into THD from being confirmed. The absolute configuration of THD, prepared by reduction of DHD in the cell-free incubation, was assigned as (3R,4S) via comparison of the retention time to that of the authentic THD by chiral chromatography. Dehydroequol (DE) was unable to produce the (3S)-equol both in the cell-free reaction and in the bacterial transformation, negating the possible intermediacy of DE. Finally, the intermediate (3R,4S)-THD was reduced into (3S)-equol by the whole cell, indicating the inversion of stereochemistry at C-3 during the reduction. A possible mechanism accounting for the racemization of DHD and the inversion of configuration of THD during reduction into (3S)-equol is proposed.

* Corresponding author. Mailing address: Program in Applied Life Chemistry, Department of Agricultural Biotechnology, College of Agriculture and Life Sciences, Seoul National University, San 56-1 Sillim-dong, Gwanak-gu, Seoul 151-921, South Korea. Phone: 82-2-880-4642. Fax: 82-2-873-3112. E-mail: soounkim{at}plaza.snu.ac.kr

{triangledown} Published ahead of print on 20 March 2009.

Applied and Environmental Microbiology, May 2009, p. 3062-3068, Vol. 75, No. 10
0099-2240/09/$08.00+0     doi:10.1128/AEM.02058-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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