Oxygen dependence of metabolic fluxes and energy generation of Saccharomyces cerevisiae CEN.PK113-1A
Oxygen dependence of metabolic fluxes and energy generation of Saccharomyces cerevisiae CEN.PK113-1A
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DOI：
10.1186/1752-0509-2-60
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发表时间：
2008-07-09
影响因子：
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通讯作者：
Maaheimo, Hannu
中科院分区：
文献类型：
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作者：
Jouhten, Paula;Rintala, Eija;Maaheimo, Hannu
背景资料：酵母酿酒酵母能够通过利用呼吸和发酵代谢模式来调节外部氧的可用性。调节代谢模式涉及改变由细胞的多级调节网络决定的细胞内代谢通量。氧是S.结果：酿酒酵母细胞内代谢通量分布与氧浓度的关系尚不清楚。酿酒酵母CEN. PK 113 -1A在葡萄糖限制的恒化培养物中生长，稀释率为0.1 h（-1），入口气体中有20.9%，2.8%，1.0%，0.5%或0.0% O（2），通过（13）C-MFA定量。利用[U-（13）C]葡萄糖分段标记实验的代谢通量比，求解了S.虽然已经在2.8%氧气中观察到乙醇生产，但与完全好氧条件相比，仅观察到通量分布的微小差异。然而，在1.0%和0.5%的氧气的呼吸速率受到严重限制，导致通过TCA循环的通量和发酵途径的主要通量的方向逐渐减少。在中心碳代谢的所有分支点中观察到通量的重新分配。然而，只有当氧气供应减少到0.5%时，生物质产量才超过乙醇和CO（2）的产量。呼吸ATP生成提供了59%的ATP需求在完全有氧条件下，仍然是一个相当大的25%，在0.5%的氧合。一个广泛的重新分配的通量在厌氧条件下观察到相比，所有的好氧条件。代谢酶的转录水平和相应的通量之间的正相关性，在不同的氧合conditions.Conclusion：（13）C-约束的MFA能够定量测定细胞内通量在不同的氧化还原挑战的条件下，不包括氧化还原辅因子代谢物的质量平衡。通量的重新分配不仅观察到呼吸，呼吸发酵和发酵代谢，但也为2.8%，1.0%和0.5%的氧气生长的细胞。虽然在这些低氧条件中的每一种中细胞代谢都是呼吸-发酵的，但是可获得的实际氧气量导致通过呼吸和发酵途径的不同贡献。
Background: The yeast Saccharomyces cerevisiae is able to adjust to external oxygen availability by utilizing both respirative and fermentative metabolic modes. Adjusting the metabolic mode involves alteration of the intracellular metabolic fluxes that are determined by the cell's multilevel regulatory network. Oxygen is a major determinant of the physiology of S. cerevisiae but understanding of the oxygen dependence of intracellular flux distributions is still scarce.Results: Metabolic flux distributions of S. cerevisiae CEN. PK113-1A growing in glucose-limited chemostat cultures at a dilution rate of 0.1 h(-1) with 20.9%, 2.8%, 1.0%, 0.5% or 0.0% O(2) in the inlet gas were quantified by (13)C-MFA. Metabolic flux ratios from fractional [U-(13)C] glucose labelling experiments were used to solve the underdetermined MFA system of central carbon metabolism of S. cerevisiae.While ethanol production was observed already in 2.8% oxygen, only minor differences in the flux distribution were observed, compared to fully aerobic conditions. However, in 1.0% and 0.5% oxygen the respiratory rate was severely restricted, resulting in progressively reduced fluxes through the TCA cycle and the direction of major fluxes to the fermentative pathway. A redistribution of fluxes was observed in all branching points of central carbon metabolism. Yet only when oxygen provision was reduced to 0.5%, was the biomass yield exceeded by the yields of ethanol and CO(2). Respirative ATP generation provided 59% of the ATP demand in fully aerobic conditions and still a substantial 25% in 0.5% oxygenation. An extensive redistribution of fluxes was observed in anaerobic conditions compared to all the aerobic conditions. Positive correlation between the transcriptional levels of metabolic enzymes and the corresponding fluxes in the different oxygenation conditions was found only in the respirative pathway.Conclusion: (13)C-constrained MFA enabled quantitative determination of intracellular fluxes in conditions of different redox challenges without including redox cofactors in metabolite mass balances. A redistribution of fluxes was observed not only for respirative, respiro-fermentative and fermentative metabolisms, but also for cells grown with 2.8%, 1.0% and 0.5% oxygen. Although the cellular metabolism was respiro-fermentative in each of these low oxygen conditions, the actual amount of oxygen available resulted in different contributions through respirative and fermentative pathways.