木糖辅助底物对近平滑假丝酵母催化(R,S)-苯基乙二醇不对称氧化还原合成(S)-苯基乙二醇体系稳定性的促进作用

通过分析近平滑假丝酵母Candida parapsilosis催化外消旋苯基乙二醇(PED)不对称氧化还原合成(S)-苯基乙二醇的反应过程,结合微生物中糖类的代谢路径研究,建立了一种以木糖为辅助底物的NADPH辅酶再生的方法,提高了该催化系统的稳定性.结果表明,相同条件下反应体系中添加8 g/L的木糖可使(S)-PED产物的对映体过量值(ee)和产率分别提高14%和10%;菌体可重复使用3~4次,而产物ee值保持在98%.考察了木糖对表达羰基还原酶重组大肠杆菌体系催化效果的影响,发现木糖是通过强化(S)-羰基还原酶的催化作用提高了催化系统的稳定性,其原因是在磷酸戊糖途径中再生了氧化还原反应所需的NADPH辅酶.

Promotion Effect of Xylose Co-substrate on Stability of Catalytic System for Asymmetric Redox of (R,S)-1-Phenyl-1,2-ethanediol to Its (S)-Enantiomer by Candida Parapsilosis

The asymmetric redox of(R,S)-1-phenyl-1,2-ethanediol to its optically active(S)-enantiomer catalyzed by Candida parapsilosis in an aqueous phase was investigated.A new efficient and economical cofactor regeneration system was established using D-xylose as the co-substrate by analyzing the reaction mechanism and the metabolic pathway of sugars in yeast.The results showed that the xylose co-substrate was advantageous for the stability of the catalytic system in a repetitive batch mode.In the presence of xylose(8 g/L),the optical purity and the yield of the(S)-enantiomer were increased by 14% and 10%,respectively.Furthermore,whole cells could be reused 34 times and the enantiomeric excess of the(S)-enantiomer remained at a high level of 98%.The effects of xylose on the accumulation of 2-hydroxyacetophenone in repetitive batch experiments and the asymmetric reaction catalyzed by carbonyl reductases from recombinant Escherichia coli were investigated.It was proposed that xylose improved the stability of the catalytic system by strengthening the(S)-carbonyl reductase system,in which NADPH that is necessary for the asymmetric reaction could be regenerated via the pentose phosphate pathway of xylose metabolism.