Enzymatic resolution of racemic phenyloxirane by a novel epoxide hydrolase from Aspergillus niger SQ-6 and its fed-batch fermentation |
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Authors: | Yanbin Liu Qian Sha Sheng Wu Jianjun Wang Liu Yang Wanru Sun |
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Institution: | (1) State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beiyitiao 13, Zhongguancun, Haidian, Beijing, 100080, People’s Republic of China;(2) Graduate School of the Chinese Academy of Sciences, Beijing, People’s Republic of China |
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Abstract: | A microorganism with the ability to catalyze the resolution of racemic phenyloxirane was isolated and identified as Aspergillus niger SQ-6. Chiral capillary electrophoresis was successfully applied to separate both phenyloxirane and phenylethanediol. The
epoxide hydrolase (EH) involved in this resolution process was (R)-stereospecific and constitutively expressed. When whole cells were used during the biotransformation process, the optimum
temperature and pH for stereospecific vicinal diol production were 35°C and 7.0, respectively. After a 24-h conversion, the
enantiomer excess of (R)-phenylethanediol produced was found to be >99%, with a conversion rate of 56%. In fed-batch fermentations at 30°C for 44 h,
glycerol (20 g L−1) and corn steep liquor (CSL) (30 g L−1) were chosen as the best initial carbon and nitrogen sources, and EH production was markedly improved by pulsed feeding of
sucrose (2 g L−1 h−1) and continuous feeding of CSL (1 g L−1 h−1) at a fermentation time of 28 h. After optimization, the maximum dry cell weight achieved was 24.5±0.8 g L−1; maximum EH production was 351.2±13.1 U L−1 with a specific activity of 14.3±0.5 U g−1. Partially purified EH exhibited a temperature optimum at 37°C and pH optimum at 7.5 in 0.1 M phosphate buffer. This study
presents the first evidence for the existence of a predicted epoxide racemase, which might be important in the synthesis of
epoxide intermediates. |
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Keywords: | Aspergillus niger Epoxide hydrolase Epoxide racemase Capillary electrophoresis Stereoselectivity |
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