Xu Zhaojun, Tsurugi Kunio
Department of Biochemistry 2, University of Yamanashi, Faculty of Medicine, 1110 Shimokato, Chuo, Yamanashi 409-3898, Japan.
Yeast. 2007 Mar;24(3):161-70. doi: 10.1002/yea.1468.
Energy-metabolism oscillation (EMO) in an aerobic chemostat culture of yeast is basically regulated by a feedback loop of redox reactions in energy metabolism and modulated by metabolism of storage carbohydrates. In this study, we investigated the role of Gts1p in the stabilization of EMO, using the GTS1-deleted transformant gts1Delta. We found that fluctuations in the redox state of the NAD co-factor and levels of redox-regulated metabolites in glycolysis, especially of ethanol, are markedly reduced in amplitude during EMO of gts1Delta, while respiration indicated by the oxygen uptake rate (OUR) and energy charge is not so affected throughout EMO in gts1Delta. Further, the transitions of the levels of OUR, NAD(+) : NADH ratio and intracellular pH between the two phases were apparently retarded compared with those in the wild-type, suggesting attenuation of EMO in gts1Delta. Furthermore, the mRNA levels of genes encoding enzymes for the synthesis of trehalose and glycogen are fairly reduced in gts1Delta, consistent with the decreased synthesis of storage carbohydrates. In addition, the level of inorganic phosphate, which is required for the reduction of NAD(+) and mainly supplied from trehalose synthesis, was decreased in the early respiro-fermentative phase in gts1Delta. Thus, we suggested that the deletion of GTS1 as a transcriptional co-activator for these genes inhibited the metabolism of storage carbohydrates, which causes attenuation of the feedback loop of dehydrogenase reactions in glycolysis with the restricted fluctuation of ethanol as a main synchronizing agent for EMO in a cell population.
酵母需氧恒化器培养中的能量代谢振荡（EMO）基本上由能量代谢中氧化还原反应的反馈回路调节，并受储存碳水化合物代谢的影响。在本研究中，我们使用缺失GTS1的转化体gts1Delta研究了Gts1p在EMO稳定中的作用。我们发现，在gts1Delta的EMO过程中，NAD辅因子的氧化还原状态波动以及糖酵解中氧化还原调节代谢物（尤其是乙醇）的水平波动幅度显著降低，而以氧气摄取率（OUR）和能量电荷表示的呼吸作用在gts1Delta的整个EMO过程中受影响较小。此外，与野生型相比，gts1Delta中OUR、NAD(+) : NADH比值和细胞内pH值在两个阶段之间的转变明显延迟，表明gts1Delta中EMO减弱。此外，gts1Delta中编码海藻糖和糖原合成酶的基因的mRNA水平大幅降低，这与储存碳水化合物合成减少一致。此外，在gts1Delta的早期呼吸发酵阶段，NAD(+)还原所需且主要由海藻糖合成提供的无机磷酸盐水平降低。因此，我们认为，作为这些基因的转录共激活因子的GTS1缺失抑制了储存碳水化合物的代谢，这导致糖酵解中脱氢酶反应的反馈回路减弱，乙醇波动受限，而乙醇是细胞群体中EMO的主要同步因子。
