PDF(Pubmed)
Abstract：
Anaerobic alcoholic fermentation, particularly in high-sugar environments, presents metabolic challenges for yeasts. Crabtree-positive yeasts, including Saccharomyces cerevisiae, prefer fermentation even in the presence of oxygen. These yeasts rely on internal NAD+ recycling and extracellular assimilation of its precursor, nicotinic acid (vitamin B3), rather than de novo NAD+ production. Surprisingly, nicotinic acid assimilation is poorly characterized, even in S. cerevisiae. This study elucidated the timing of nicotinic acid uptake during grape juice-like fermentation and its impact on NAD(H) levels, the NAD+/NADH ratio, and metabolites produced. Complete uptake of extracellular nicotinic acid occurred premid-exponential phase, thereafter small amounts of vitamin B3 were exported back into the medium. Suboptimal levels of nicotinic acid were correlated with slower fermentation and reduced biomass, disrupting redox balance and impeding NAD+ regeneration, thereby affecting metabolite production. Metabolic outcomes varied with nicotinic acid concentrations, linking NAD+ availability to fermentation efficiency. A model was proposed encompassing rapid nicotinic acid uptake, accumulation during cell proliferation, and recycling with limited vitamin B3 export. This research enhances the understanding of nicotinic acid uptake dynamics during grape juice-like fermentation. These insights contribute to advancing yeast metabolism research and have profound implications for the enhancement of biotechnological practices and the wine-making industry.
摘要：
厌氧酒精发酵，特别是在高糖环境中，对酵母菌提出了代谢挑战。Crabtree阳性酵母,包括酿酒酵母,即使在氧气存在的情况下也喜欢发酵。这些酵母依赖于其前体的内部NAD再循环和细胞外同化，烟酸（维生素B3），而不是从头NAD+生产。令人惊讶的是,烟酸同化的特征很差，甚至在酿酒酵母中。本研究阐明了葡萄汁样发酵过程中烟酸摄取的时间及其对NAD（H）水平的影响，NAD+/NADH比率，和产生的代谢物。细胞外烟酸的完全摄取发生在指数中期前，此后少量的维生素B3被输出回培养基中.烟酸的次优水平与发酵较慢和生物量降低相关，破坏氧化还原平衡，阻碍NAD+再生，从而影响代谢物的产生。代谢结果随烟酸浓度而变化，将NAD+可用性与发酵效率联系起来。提出了一个包含快速烟酸吸收的模型，细胞增殖过程中的积累，和回收利用有限的维生素B3出口。这项研究增强了对葡萄汁状发酵过程中烟酸吸收动力学的理解。这些见解有助于推进酵母代谢研究，并对加强生物技术实践和酿酒行业具有深远的意义。
