Departamento de Bioquímica, Instituto Nacional de Cardiología Ignacio Chávez, Tlalpan, Mexico.
FEBS J. 2013 Nov;280(22):5737-49. doi: 10.1111/febs.12490. Epub 2013 Sep 13.
To determine the extent to which the supply of the precursor 2-oxoglutarate (2-OG) controls the synthesis of lysine in Saccharomyces cerevisiae growing exponentially in high glucose, top-down elasticity analysis was used. Three groups of reactions linked by 2-OG were defined. The 2-OG supply group comprised all metabolic steps leading to its formation, and the two 2-OG consumer groups comprised the enzymes and transporters involved in 2-OG transformation into lysine and glutamate and their further utilization for protein synthesis and storage. Various 2-OG steady-state concentrations that produced different fluxes to lysine and glutamate were attained using yeast mutants with increasing activities of Krebs cycle enzymes and decreased activities of Lys synthesis enzymes. The elasticity coefficients of the three enzyme groups were determined from the dependence of the amino acid fluxes on the 2-OG concentration. The respective degrees of control on the flux towards lysine (flux control coefficients) were determined from their elasticities, and were 1.1, 0.41 and -0.52 for the 2-OG producer group and the Lys and Glu branches, respectively. Thus, the predominant control exerted by the 2-OG supply on the rate of lysine synthesis suggests that over-expression of 2-OG producer enzymes may be a highly effective strategy to enhance Lys production.
为了确定前体 2-氧戊二酸（2-OG）的供应在多大程度上控制了酿酒酵母在高葡萄糖中指数生长时赖氨酸的合成，采用了自上而下的弹性分析。定义了三组通过 2-OG 连接的反应。2-OG 供应组包括所有导致其形成的代谢步骤，而 2-OG 两个消费者群体包括参与 2-OG 转化为赖氨酸和谷氨酸的酶和转运蛋白，以及它们进一步用于蛋白质合成和储存。通过使用克雷布斯循环酶活性增加和赖氨酸合成酶活性降低的酵母突变体，可以获得产生不同赖氨酸和谷氨酸通量的各种 2-OG 稳态浓度。从氨基酸通量对 2-OG 浓度的依赖性确定了这三个酶组的弹性系数。从它们的弹性得出了各酶组对赖氨酸通量的控制程度（通量控制系数），对于 2-OG 产生组和 Lys 和 Glu 分支，分别为 1.1、0.41 和-0.52。因此，2-OG 供应对赖氨酸合成速率的主要控制作用表明，过表达 2-OG 产生酶可能是提高 Lys 产量的一种非常有效的策略。
