Sierkstra L N, Nouwen N P, Verbakel J M, Verrips C T
Department of Molecular Cell Biology, University of Utrecht, The Netherlands.
Yeast. 1993 Jul;9(7):787-95. doi: 10.1002/yea.320090713.
In order to determine whether the changes in the activities and mRNA levels of enzymes involved in intermediary carbon metabolism previously observed in glucose-limited continuous cultures (Sierkstra et al., 1992a) were glucose specific, we have analysed their regulation in a galactose-limited continuous culture of Saccharomyces cerevisiae. The Vmax of the galactose uptake system was shown to be dilution rate (D) dependent, comparable with the high-affinity glucose uptake. The maximum uptake was observed at D 0.2 h-1 (0.25 mmol min-1 per g) and the minimum uptake (0.1 mmol min-1 per g) at D 0.05 h-1 and 0.3 h-1. The aerobic fermentation of galactose occurred at D 0.275-0.3 h-1 which is identical to the results obtained in glucose-limited continuous cultures of this strain. Because galactose is not a repressing carbon source, this demonstrates that the Crabtree effect is not mediated by, or in any way related to glucose repression. Moreover, invertase and hexokinase I mRNA levels (both subject to glucose repression at the transcriptional level) were present when the yeast produced ethanol in galactose- and glucose-limited continuous cultures. In glucose-limited continuous cultures a decrease in alcohol dehydrogenase (I and II) mRNA levels and activity and phosphoglucomutase activity was observed with increasing dilution rates. In addition, at D 0.3 h-1, when the yeast produced ethanol, glucose-6-phosphate dehydrogenase and pyruvate decarboxylase were induced and a decrease in respiration was observed.(ABSTRACT TRUNCATED AT 250 WORDS)
为了确定先前在葡萄糖限制的连续培养物中观察到的（Sierkstra等人，1992a）中间碳代谢相关酶的活性和mRNA水平变化是否具有葡萄糖特异性，我们分析了它们在酿酒酵母半乳糖限制连续培养物中的调控情况。半乳糖摄取系统的Vmax显示出与稀释率（D）相关，与高亲和力葡萄糖摄取相当。在D为0.2 h-1（每克0.25 mmol min-1）时观察到最大摄取量，在D为0.05 h-1和0.3 h-1时观察到最小摄取量（每克0.1 mmol min-1）。半乳糖的有氧发酵发生在D为0.275 - 0.3 h-1时，这与该菌株在葡萄糖限制连续培养物中获得的结果相同。由于半乳糖不是抑制性碳源，这表明克奈特效应不是由葡萄糖阻遏介导的，也不以任何方式与之相关。此外，当酵母在半乳糖和葡萄糖限制的连续培养物中产生乙醇时，存在转化酶和己糖激酶I的mRNA水平（两者在转录水平上都受葡萄糖阻遏）。在葡萄糖限制的连续培养物中，随着稀释率的增加，观察到乙醇脱氢酶（I和II）的mRNA水平和活性以及磷酸葡萄糖变位酶活性降低。此外，在D为0.3 h-1时，当酵母产生乙醇时，葡萄糖-6-磷酸脱氢酶和丙酮酸脱羧酶被诱导，并且观察到呼吸作用降低。（摘要截短至250字）
