MSU-DOE Plant Research Laboratory, Michigan State University, 210 Wilson Road, East Lansing, MI 48824, U.S.A.
Department of Biochemistry and Molecular Biology, Michigan State University, 603 Wilson Road, East Lansing, MI 48824, U.S.A.
Biochem J. 2019 May 31;476(10):1539-1551. doi: 10.1042/BCJ20190234.
Glucose-6-phosphate dehydrogenase (G6PDH) can initiate the glucose-6-phosphate (G6P) shunt around the Calvin-Benson cycle. To understand the regulation of flux through this pathway, we have characterized the biochemical parameters and redox regulation of the three functional plastidic isoforms of G6PDH. When purified, recombinant proteins were measured, all three exhibited significant substrate inhibition by G6P but not NADP, making the determination of enzyme kinetic parameters complex. We found that the half-saturation concentration of G6PDH isoform 1 is increased under reducing conditions. The other two isoforms exhibit less redox regulation, however, isoform 2 is strongly inhibited by NADPH. Redox regulation of G6PDH1 can be partially reversed by hydrogen peroxide or protected against by the presence of its substrate, G6P. Overall, our results support the conclusion that G6PDH can have significant activity throughout the day and can be dynamically regulated to allow or prevent flux through the glucose-6-phosphate shunt.
葡萄糖-6-磷酸脱氢酶（G6PDH）可以启动卡尔文-本森循环周围的葡萄糖-6-磷酸（G6P）分流。为了了解该途径通量的调节，我们已经对三种功能性质体 G6PDH 同工型的生化参数和氧化还原调节进行了表征。在纯化时，测量重组蛋白，所有三种同工型都表现出对 G6P 的显著底物抑制，但对 NADP 没有抑制，这使得酶动力学参数的确定变得复杂。我们发现同工型 1 的 G6PDH 的半饱和浓度在还原条件下增加。另外两种同工型表现出较少的氧化还原调节，但同工型 2 被 NADPH 强烈抑制。G6PDH1 的氧化还原调节可以部分被过氧化氢逆转，或者通过其底物 G6P 的存在来保护。总的来说，我们的结果支持以下结论：G6PDH 可以在一天中保持相当高的活性，并可以通过动态调节来允许或阻止葡萄糖-6-磷酸分流的通量。
