Sierkstra L N, Verbakel J M, Verrips C T
Department of Molecular Cell Biology, University of Utrecht, The Netherlands.
J Gen Microbiol. 1992 Dec;138(12):2559-66. doi: 10.1099/00221287-138-12-2559.
mRNA steady-state levels and activities of enzymes of intermediary carbon metabolism (hexokinase, phosphoglucoisomerase, phosphofructokinase, glucose-6-phosphate dehydrogenase, phosphoglucomutase) and glucose-regulated enzymes (pyruvate decarboxylase, pyruvate dehydrogenase, invertase, alcohol dehydrogenase) were determined in glucose-limited continuous cultures of an industrial strain of Saccharomyces cerevisiae at different dilution rates (D) ranging from 0.05 to 0.315 h-1. The activity of most enzymes measured remained constant over this range except for alcohol dehydrogenase I/II which decreased proportionally with increasing dilution rate. A decrease in phosphoglucomutase activity occurred with increasing dilution rate but reached a minimum at D 0.2 h-1 and from thereon remained constant. A decrease in pyruvate decarboxylase activity and a slight decrease in phosphoglucoisomerase activity was observed. At D 0.29/0.315 h-1, at the onset of the Crabtree effect, most glycolytic enzymes remained constant except for pyruvate decarboxylase and glucose-6-phosphate dehydrogenase which increased at D 0.315 h-1 and alcohol dehydrogenase I/II which decreased. The ADHI/II and PDC1 mRNA levels obtained at the different dilution rates were in accordance with the activity measurements. The mRNA level of HXK1 decreased with increasing dilution rates, whereas the transcription of HXK2 increased. Pyruvate dehydrogenase (PDA1) and PGI1 mRNA fluctuated but no significant change could be detected. These results indicate that there is no transcriptional or translational regulation of glycolytic flux between D 0.05 h-1 and 0.315 h-1 except at the branch point between oxidative and fermentative metabolism (pyruvate decarboxylase/pyruvate dehydrogenase) at D 0.315 h-1. Surprisingly regulation of the Crabtree effect does not seem to involve transcriptional regulation of PDA1.(ABSTRACT TRUNCATED AT 250 WORDS)
在不同稀释率（D）范围为0.05至0.315 h⁻¹的条件下，对工业酿酒酵母菌株进行葡萄糖限制连续培养，测定了mRNA稳态水平以及中间碳代谢酶（己糖激酶、磷酸葡萄糖异构酶、磷酸果糖激酶、葡萄糖-6-磷酸脱氢酶、磷酸葡萄糖变位酶）和葡萄糖调节酶（丙酮酸脱羧酶、丙酮酸脱氢酶、转化酶、乙醇脱氢酶）的活性。除乙醇脱氢酶I/II随稀释率增加成比例下降外，在此范围内所测的大多数酶活性保持恒定。磷酸葡萄糖变位酶活性随稀释率增加而降低，但在D为0.2 h⁻¹时达到最小值，此后保持恒定。观察到丙酮酸脱羧酶活性降低以及磷酸葡萄糖异构酶活性略有下降。在D为0.29/0.315 h⁻¹，即克奈特效应开始时，除丙酮酸脱羧酶和葡萄糖-6-磷酸脱氢酶在D为0.315 h⁻¹时增加以及乙醇脱氢酶I/II降低外，大多数糖酵解酶保持恒定。在不同稀释率下获得的ADHI/II和PDC1 mRNA水平与活性测量结果一致。HXK1的mRNA水平随稀释率增加而降低，而HXK2的转录增加。丙酮酸脱氢酶（PDA1）和PGI1 mRNA有波动，但未检测到显著变化。这些结果表明，在D为0.05 h⁻¹至0.315 h⁻¹之间，除了在D为0.315 h⁻¹时氧化代谢与发酵代谢的分支点（丙酮酸脱羧酶/丙酮酸脱氢酶）外，糖酵解通量不存在转录或翻译调控。令人惊讶的是，克奈特效应的调控似乎不涉及PDA1的转录调控。（摘要截短至250字）
