Zhang Yanping, Huang Zhihua, Du Chenyu, Li Yin, Cao Zhu'an
Department of Chemical Engineering, Tsinghua University, Beijing, China.
Metab Eng. 2009 Mar;11(2):101-6. doi: 10.1016/j.ymben.2008.11.001. Epub 2008 Nov 25.
Redox cofactors play crucial roles in the metabolic and regulatory network of living organisms. We reported here the effect of introducing a heterogeneous NADH regeneration system into Klebsiella oxytoca on cell growth and glycerol metabolism. Expression of fdh gene from Candida boidinii in K. oxytoca resulted in higher intracellular concentrations of both NADH and NAD(+) during the fermentation metaphase, with the ratio of NADH to NAD(+) unaltered and cell growth unaffected, interestingly different from that in engineered Escherichia coli, Lactococcus lactis, and others. Metabolic flux analysis revealed that fluxes to 1,3-propanediol, ethanol, and lactate were all increased, suggesting both the oxidative and reductive metabolisms of glycerol were enhanced. It demonstrates that in certain microbial system NADH availability can be increased with NADH to NAD(+) ratio unaltered, providing a new strategy to improve the metabolic flux in those microorganisms where glycolysis is not the only central metabolic pathways.
氧化还原辅因子在生物体的代谢和调节网络中起着至关重要的作用。我们在此报告了将异质NADH再生系统引入产酸克雷伯菌对细胞生长和甘油代谢的影响。来自博伊丁假丝酵母的fdh基因在产酸克雷伯菌中的表达导致发酵中期细胞内NADH和NAD(+)浓度均升高，NADH与NAD(+)的比例未改变且细胞生长未受影响，有趣的是这与工程化大肠杆菌、乳酸乳球菌等不同。代谢通量分析表明，通向1,3 - 丙二醇、乙醇和乳酸的通量均增加，表明甘油的氧化代谢和还原代谢均得到增强。这表明在某些微生物系统中，可以在不改变NADH与NAD(+)比例的情况下增加NADH的可用性，为改善那些糖酵解不是唯一核心代谢途径的微生物的代谢通量提供了一种新策略。
