Hao Meng-Shu, Jensen Anna M, Boquist Ann-Sofie, Liu Yun-Jun, Rasmusson Allan G
Department of Biology, Lund University, Lund, Sweden.
Department of Biology, Lund University, Lund, Sweden; Department of Forestry and Wood Technology, Linnaeus University, Växjö, Sweden.
PLoS One. 2015 Sep 28;10(9):e0139224. doi: 10.1371/journal.pone.0139224. eCollection 2015.
NADPH is a key reductant carrier that maintains internal redox and antioxidant status, and that links biosynthetic, catabolic and signalling pathways. Plants have a mitochondrial external NADPH oxidation pathway, which depends on Ca2+ and pH in vitro, but concentrations of Ca2+ needed are not known. We have determined the K0.5(Ca2+) of the external NADPH dehydrogenase from Solanum tuberosum mitochondria and membranes of E. coli expressing Arabidopsis thaliana NDB1 over the physiological pH range using O2 and decylubiquinone as electron acceptors. The K0.5(Ca2+) of NADPH oxidation was generally higher than for NADH oxidation, and unlike the latter, it depended on pH. At pH 7.5, K0.5(Ca2+) for NADPH oxidation was high (≈100 μM), yet 20-fold lower K0.5(Ca2+) values were determined at pH 6.8. Lower K0.5(Ca2+) values were observed with decylubiquinone than with O2 as terminal electron acceptor. NADPH oxidation responded to changes in Ca2+ concentrations more rapidly than NADH oxidation did. Thus, cytosolic acidification is an important activator of external NADPH oxidation, by decreasing the Ca2+-requirements for NDB1. The results are discussed in relation to the present knowledge on how whole cell NADPH redox homeostasis is affected in plants modified for the NDB1 gene.
还原型辅酶Ⅱ（NADPH）是一种关键的还原剂载体，它维持着细胞内的氧化还原和抗氧化状态，并连接生物合成、分解代谢和信号传导途径。植物具有一条线粒体外部NADPH氧化途径，该途径在体外依赖Ca2+和pH值，但所需的Ca2+浓度尚不清楚。我们使用氧气和癸基泛醌作为电子受体，在生理pH范围内测定了马铃薯线粒体和表达拟南芥NDB1的大肠杆菌膜中外源NADPH脱氢酶的K0.5（Ca2+）。NADPH氧化的K0.5（Ca2+）通常高于NADH氧化的K0.5（Ca2+），并且与后者不同的是，它依赖于pH值。在pH 7.5时，NADPH氧化的K0.5（Ca2+）较高（≈100μM），而在pH 6.8时测定的K0.5（Ca2+）值低20倍。与以氧气作为末端电子受体相比，以癸基泛醌作为末端电子受体时观察到更低的K0.5（Ca2+）值。NADPH氧化对Ca2+浓度变化的响应比NADH氧化更快。因此，细胞质酸化是外部NADPH氧化的重要激活剂，它通过降低NDB1对Ca2+的需求来实现。我们结合目前关于NDB1基因修饰植物中全细胞NADPH氧化还原稳态如何受到影响的知识对这些结果进行了讨论。
