Elucidation of a Self-Sustaining Cycle in Escherichia colil-Serine Biosynthesis That Results in the Conservation of the Coenzyme, NAD+,Biochemistry

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Elucidation of a Self-Sustaining Cycle in Escherichia colil-Serine Biosynthesis That Results in the Conservation of the Coenzyme, NAD+
Biochemistry ( IF 2.9 ) Pub Date : 2018-03-01 00:00:00 , DOI: 10.1021/acs.biochem.8b00074
Gregory A. Grant ₁

Affiliation

The equilibrium of the reaction catalyzed by d-3-phosphoglycerate dehydrogenase (PGDH), the first enzyme in the l-serine biosynthetic pathway, is far in the direction away from serine synthesis. As such, the enzyme is usually assayed in this direction. To easily assay it in the direction of l-serine synthesis, it can be coupled to the next enzyme in the pathway, phosphoserine aminotransferase (PSAT), with the activity monitored by the conversion of NAD⁺ to NADH by PGDH. However, when PGDHs from several different species were coupled to PSAT, it was found that one of them, ecPGDH, conserves the coenzyme in the production of l-serine by utilizing an intrinsic cycle of NAD⁺/NADH interconversion coupled with the conversion of α-ketoglutarate (αKG) to α-hydroxyglutarate. Furthermore, the cycle can be maintained by production of αKG by the second enzyme in the pathway, PSAT, and does not require any additional enzymes. This is not the case for PGDH from another bacterial source, Mycobacterium tuberculosis, and a mammalian source, human liver, where net consumption of NAD⁺ occurs. Both NAD⁺ and NADH appear to remain tightly bound to ecPGDH during the cycle, effectively removing a requirement for the presence of an exogenous coenzyme pool to maintain the pathway and significantly reducing the energy requirement needed to maintain this major metabolic pathway.

中文翻译：

阐明大肠杆菌L-丝氨酸生物合成中的自我维持周期，该过程导致辅酶NAD ⁺的保守

由d -3-磷酸甘油酸脱氢酶（PGDH）催化的反应平衡是远离丝氨酸合成的方向，而PGDH是1-丝氨酸生物合成途径中的第一个酶。因此，通常沿该方向测定酶。容易地测定它在方向升-丝氨酸的合成，它可以耦合到在所述途径中，磷酸丝氨酸氨基转移酶（PSAT）下一酶，与活动监测由NAD的转化⁺至NADH通过PGDH。然而，当从几个不同的物种PGDHs偶联至PSAT，发现它们中的一个，EC PGDH，节省生产辅酶升通过利用NAD的固有周期-丝氨酸⁺ / NADH互变，同时将α-酮戊二酸（αKG）转化为α-羟基戊二酸。此外，可以通过途径中的第二种酶PSAT产生αKG来维持循环，并且不需要任何其他酶。来自另一细菌来源的结核分枝杆菌和哺乳动物来源的人肝脏的PGDH并非如此，在那儿会发生NAD ^+的净消耗。在循环过程中，NAD ⁺和NADH似乎都与ec PGDH保持紧密结合，从而有效地消除了维持外源辅酶池以维持该途径的需求，并显着降低了维持该主要代谢途径所需的能量需求。

更新日期：2018-03-01

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