CTAB透性化酵母细胞生物催化合成(S)-(+)-3-羟基丁酸乙酯

Biocatalytic Synthesis of Ethyl (S)-(+)-3-Hydroxybutanoate by CTAB-Permeabilized Baker's Yeast Cells

利用十六烷基三甲基溴化铵(CTAB)透性化啤酒酵母细胞中高活性的脱氢酶,借助于辅助底物乙醇和葡萄糖,对3羰基丁酸乙酯(EOB)不对称还原合成(S)(+)3羟基丁酸乙酯((S)(+)3EHB)进行了研究.结果表明,CTAB透性化酵母细胞中的醇脱氢酶和6磷酸葡萄糖脱氢酶的活性分别比未经处理的酵母细胞高482倍和6.5倍.在相同条件下,CTAB透性化细胞对EOB的还原比未经处理的酵母细胞快.细胞浓度对反应有明显影响,当透性化酵母细胞浓度<90mg/ml时,(S)(+)3EHB的产率和对映体过量值都较低;当酵母细胞浓度≥90mg/ml,在最佳进料速率、最适温度和pH条件下,振摇速度为125r/min时,(S)(+)3EHB的浓度达到最大值314mmol/L.在反应开始的6h内,(S)(+)3EHB的产率可达94%,对映体过量值≥98%,但24h后产率和对映体过量值分别降低到85%和91%.

The asymmetric reduction of ethyl 3-oxobutanoate (EOB) to ethyl ( S)-( +)-3-hydroxybutanoate ((S)-(+)-3-EHB) catalyzed by dehydrogenases with high activity in cetyltrimethylammonium bromide (CTAB) permeabilized baker's yeast cells using alcohol and glucose as co-substrates was studied. The results showed that the activity of the alcohol dehydrogenase and glucose-6- phosphate dehydrogenase in the permeabilized cells increased 482-fold and 6.5-fold, respectively, compared with those in the control cells. The concentration of the permeabilized cells was particularly important for the high yield and selectivity in aerobic conditions and in the medium containing alcohol and glucose. EOB was reduced faster by the permeabilized cells than by the control cells. Both the yield and the enantiomeric excess of (S)- (+)-3-EHB were low when the cell concentration was less than 90 mg/ml. The highest (S)- (+)-3-EHB concentration of 314 mmol/L was obtained with >= 90 mg/ml of the permeabilized cells at the optimized pH, temperature and feeding rate. During the first 6 h, the yield and enantiomeric excess reached 94 % and 98 %, respectively, but decreased to 91 % and 85 % after 24 h.