Heux Stéphanie, Cachon Rémy, Dequin Sylvie
UMR Sciences pour l'Oenologie, Microbiologie, INRA, 2 place Viala, F-34060 Montpellier Cedex 1, France.
Metab Eng. 2006 Jul;8(4):303-14. doi: 10.1016/j.ymben.2005.12.003. Epub 2006 Feb 10.
The pyridine nucleotides NAD(H) and NADP(H) play major roles in the formation of by-products. To analyse how Saccharomyces cerevisiae (S. cerevisiae) metabolism during growth on glucose might be altered when intracellular NADH pool is decreased, we expressed noxE encoding a water-forming NADH oxidase from Lactococcus lactis (L. lactis) in the S. cerevisiae strain V5. During batch fermentation under controlled microaeration conditions, expression of the NADH oxidase under the control of a yeast promoter lead to large decreases in the intracellular NADH concentration (five-fold) and NADH/NAD+ ratio (six-fold). This increased NADH consumption caused a large redistribution of metabolic fluxes. The ethanol, glycerol, succinate and hydroxyglutarate yields were significantly reduced as a result of the lower NADH availability, whereas the formation of more oxidized metabolites, acetaldehyde, acetate and acetoin was favoured. The biomass yield was low and consumption of glucose, at concentration above 10%, was impaired. The metabolic redistribution in cells expressing the NADH oxidase was a consequence of the maintenance of a redox balance and of the management of acetaldehyde formation, which accumulated at toxic levels early in the process.
吡啶核苷酸NAD(H)和NADP(H)在副产物形成中起主要作用。为了分析当细胞内NADH库减少时，酿酒酵母在葡萄糖上生长期间的代谢可能如何改变，我们在酿酒酵母菌株V5中表达了编码来自乳酸乳球菌的产水NADH氧化酶的noxE。在受控微需氧条件下的分批发酵过程中，在酵母启动子控制下的NADH氧化酶的表达导致细胞内NADH浓度大幅下降（五倍）和NADH/NAD+比率大幅下降（六倍）。这种NADH消耗的增加导致了代谢通量的大量重新分配。由于NADH可用性降低，乙醇、甘油、琥珀酸和羟基戊二酸的产量显著降低，而更氧化的代谢物乙醛、乙酸和乙偶姻的形成则受到青睐。生物量产量较低，浓度高于10%的葡萄糖消耗受到损害。表达NADH氧化酶的细胞中的代谢重新分配是维持氧化还原平衡和管理乙醛形成的结果，乙醛在该过程早期积累到有毒水平。
