Institut für Biotechnologie, Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany.
Biotechnol Bioeng. 1997 Oct 20;56(2):168-80. doi: 10.1002/(SICI)1097-0290(19971020)56:2<168::AID-BIT6>3.0.CO;2-N.
To evaluate the importance of reactions within the central metabolism under different flux burdens the fluxes within the pentose phosphate pathway (PPP), as well as the other reactions of the central metabolism, were intensively analyzed and quantitated. For this purpose, Corynebacterium glutamicum was grown with [1-(13)C]glucose to metabolic and isotopic steady state and the fractional enrichments in precursor metabolites (e.g., pentose 5-phosphate) were quantified. Matrix calculus was used to express these data together with metabolite mass data. The detailed analysis of the dependence of (13)C enrichments on exchange fluxes enabled the transketolase-catalyzed exchange rate (2 pentose 5-phosphate <--> sedoheptulose 7-phosphate + glyceraldehyde 3-phosphate) to be quantified as 74.3% (molar metabolite flux) at a net flux of 10.3% and the exchange rate (pentose 5-phosphate + erythrose 4-phosphate <--> fructose 6-phosphate + glyceraldehyde 3-phosphate) to be quantified as 5.6% at a net flux of 8.1%. The flux entering the tricarboxylic acid cycle was 93.3%. The same comprehensive flux analysis as performed for the nonexcreting condition was done with the identical strain that had been forced to excrete L-glutamate. Because we had already quantified the fluxes for L-lysine excretion with an isogenic strain, three directly comparable flux situations are thus available. Consequently, this comparison permits a direct cause-and-effect relationship to be specified. In response to the different flux burdens of the cell, the PPP flux decreased from a maximum of 67% to 26%, with the glycolytic flux increasing accordingly. The carbon flux through isocitrate dehydrogenase increased from 20% to 36%. The bidirectional carbon flux between pyruvate and oxaloacetate decreased from 36% to 9%. Since the cause of the three different flux states was the allelic exchange in the final L-lysine assembling pathway or the glutamate export activity, respectively, the flexible response is the effect. This shows conclusively the enormous flexibility within the central metabolism of C. glutamicum to supply precursors upon their withdrawal for the synthesis of amino acids. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 168-180, 1997.
为了评估在不同通量负荷下中心代谢物内反应的重要性，对戊糖磷酸途径 (PPP) 以及中心代谢的其他反应的通量进行了深入分析和定量。为此，将谷氨酸棒杆菌用 [1-(13)C]葡萄糖培养至代谢和同位素稳态，并定量了前体代谢物（如戊糖 5-磷酸）的分数丰度。使用矩阵微积分将这些数据与代谢物质量数据结合起来。对 (13)C 丰度与交换通量之间的依赖关系的详细分析，使转酮醇酶催化的交换速率（2 个戊糖 5-磷酸 <--> 景天庚酮糖 7-磷酸 + 甘油醛 3-磷酸）能够被量化为 74.3%（摩尔代谢物通量），在净通量为 10.3%时，以及交换速率（戊糖 5-磷酸 + 赤藓糖 4-磷酸 <--> 果糖 6-磷酸 + 甘油醛 3-磷酸）能够被量化为 5.6%，在净通量为 8.1%时。进入三羧酸循环的通量为 93.3%。对于非排泄条件下进行的相同综合通量分析，使用相同的菌株进行，该菌株被迫排泄 L-谷氨酸。因为我们已经使用同基因菌株量化了 L-赖氨酸排泄的通量，因此有三个可直接比较的通量情况。因此，这种比较可以指定直接的因果关系。为了应对细胞的不同通量负荷，PPP 通量从最大值 67%下降到 26%，同时糖酵解通量相应增加。异柠檬酸脱氢酶的碳通量从 20%增加到 36%。丙酮酸和草酰乙酸之间的双向碳通量从 36%下降到 9%。由于三种不同通量状态的原因分别是最终 L-赖氨酸组装途径中的等位基因交换或谷氨酸外排活性，因此灵活的响应是其结果。这清楚地表明，谷氨酸棒杆菌的中心代谢具有巨大的灵活性，可以在合成氨基酸时提供前体。（c）1997 年 John Wiley & Sons，Inc. 生物技术与生物工程 56:168-180，1997 年。
