Wenhao Qu,Yajun Bai,Tai-Ping Fan,Xiaohui Zheng,Yujie Cai
Lactobacillus reuteri DSM20016 has several aldo-keto reductases (AKRs), and they were heterologously expressed in E. coli BL21 (DE3) in this study. Subsequently, these AKRs were purified, and their enzymatic properties were investigated. It was found that these enzymes used NADPH as coenzyme and did not depend on metal ions. The optimum pH of these AKRs was a slightly acidic (AKR-1 and AKR-6: 5.5; AKR-3 and AKR-8: 6; AKR-2 and AKR-4: 6.5). These enzymes had a broad substrate spectrum and could convert a variety of aldehydes to alcohols; however, they did not catalyze the reverse reactions. All results showed that Lactobacillus reuteri had the ability to produce various volatile compounds, which allowed Lactobacillus reuteri to impart complex aroma to something.
Zhenghong Hu,Pu Jia,Yajun Bai,Tai-ping Fan,Xiaohui Zheng,Yujie Cai
Alcohol dehydrogenases convert aldehydes causing volatile aromas in cheese into corresponding alcohols. In this study, we cloned and recombinantly produced five novel ADHs from Lactobacillus reuteri DSM20016 in Escherichia coli BL21 (DE3). The resulting proteins have molecular weights between 35 and 39 kDa. The optimum pH for enzyme activity of ADH-1, ADH-2 and ADH-3 was weakly acidic (pH 5, 6 and 5, respectively), compared with pH 7 for ADH-4 and ADH-5. The optimum temperature range for ADH-1, ADH-3, ADH-4 and ADH-5 was 40 °C ―55 °C, compared with 35 °C for ADH-2. These enzymes reduced a broad range of substrates; the highest catalytic efficiency and substrate affinity for ADH-1 was observed with heptaldehyde (K cat /K m = 39.4 s −1 ·mM −1 , K m = 0.459 mM), while 3-methylbutanal was the best substrate for ADH-5 (K cat /K m = 24.0 s −1 ·mM −1 , K m = 1.35 × 10 −2 mM). ADH-2, ADH-3 and ADH-4 exhibited the highest substrate affinity for valeraldehyde, propionaldehyde, and hexanal, respectively (K m = 1.19 × 10 −2 mM, 2.81 × 10 −2 mM, 1.35 × 10 −2 mM). The enzymatic properties indicated that these enzymes effectively converted fragrant compounds during cheese ripening.
危险品化学品经营许可证（带存储）