Department of Applied Microbiology, Chemical Center, University of Lund, P.O. Box 124, S-221 00 Lund, Sweden.
Appl Environ Microbiol. 1990 Jan;56(1):120-6. doi: 10.1128/aem.56.1.120-126.1990.
Glucose and xylulose fermentation and product formation by Saccharomyces cerevisiae were compared in batch culture under anaerobic conditions. In both cases the main product was ethanol, with glycerol, xylitol, and arabitol produced as by-products. During glucose and xylulose fermentation, 0.74 and 0.37 g of cell mass liter, respectively, were formed. In glucose-fermenting cells, the carbon balance could be closed, whereas in xylulose-fermenting cells, about 25% of the consumed sugar carbon could not be accounted for. The rate of sugar consumption was 3.94 mmol g of initial biomass h for glucose and 0.39 mmol g of initial biomass h for xylulose. Concentrations of the intermediary metabolites fructose-1,6-diphosphate (FDP), pyruvate (PYR), sedoheptulose 7-phosphate (S7P), erytrose 4-phosphate, citrate (CIT), fumarate, and malate were compared for both types of cells. Levels of FDP, PYR, and CIT were lower, and levels of S7P were higher in xylulose-fermenting cells. After normalization to the carbon consumption rate, the levels of FDP were approximately the same, whereas there was a significant accumulation of S7P, PYR, CIT, and malate, especially of S7P, in xylulose-fermenting cells compared with in glucose-fermenting cells. In the presence of 15 muM iodoacetate, an inhibitor of the enzyme glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.12), FDP levels increased and S7P levels decreased in xylulose-assimilating cells compared with in the absence of the inhibitor, whereas fermentation was slightly slowed down. The specific activity of transaldolase (EC 2.2.1.2), the pentose phosphate pathway enzyme reacting with S7P and glyceraldehyde-3-phosphate, was essentially the same for both glucose- and xylulose-fermenting cells. It was, however, several orders of magnitude lower than that reported for a Torula yeast and Candida utilis. The presence of iodoacetate did not influence the activity of transaldolase in xylulose-fermenting cells. The results are discussed in terms of a competition between the pentose phosphate pathway and glycolysis for the common metabolite, glyceraldehyde-3-phosphate, which would explain the low rates of xylulose assimilation and ethanol production from xylulose by S. cerevisiae.
在厌氧条件下的分批培养中，比较了酿酒酵母对葡萄糖和木糖的发酵和产物形成。在这两种情况下，主要产物都是乙醇，同时还产生了甘油、木糖醇和阿糖醇等副产品。在葡萄糖和木糖发酵过程中，分别形成了 0.74 和 0.37 g/L 的细胞质量。在葡萄糖发酵细胞中，可以封闭碳平衡，而在木糖发酵细胞中，约 25%的消耗糖碳无法解释。糖的消耗速率为 3.94 mmol g 初始生物质 h 用于葡萄糖和 0.39 mmol g 初始生物质 h 用于木糖。比较了两种类型细胞的中间代谢物果糖-1,6-二磷酸 (FDP)、丙酮酸 (PYR)、景天庚酮糖 7-磷酸 (S7P)、赤藓糖 4-磷酸、柠檬酸 (CIT)、富马酸和苹果酸的浓度。在木糖发酵细胞中，FDP、PYR 和 CIT 的水平较低，而 S7P 的水平较高。归一化到碳消耗速率后，FDP 的水平大致相同，而 S7P、PYR、CIT 和苹果酸，尤其是 S7P 的积累量显著增加，与葡萄糖发酵细胞相比，木糖发酵细胞中 S7P、PYR、CIT 和苹果酸的积累量显著增加。在 15 μM 碘乙酸存在下，一种甘油醛-3-磷酸脱氢酶 (EC 1.2.1.12) 的抑制剂，与不存在抑制剂相比，FDP 水平在木糖同化细胞中增加，S7P 水平降低，而发酵速度略有减慢。转醛醇酶 (EC 2.2.1.2) 的比活度，与 S7P 和甘油醛-3-磷酸反应的戊糖磷酸途径酶，对于葡萄糖和木糖发酵细胞基本相同。然而，它比报道的用于Torula 酵母和 Candida utilis 的比活度低几个数量级。碘乙酸的存在并不影响木糖发酵细胞中转醛醇酶的活性。这些结果是根据甘油醛-3-磷酸在戊糖磷酸途径和糖酵解之间的竞争来讨论的，这可以解释酿酒酵母对木糖的低同化率和从木糖生产乙醇的低速率。
