GLYCOLATE OXIDASE3, a Glycolate Oxidase Homolog of Yeast L-Lactate Cytochrome c Oxidoreductase, Supports L-Lactate Oxidation in Roots of Arabidopsis
GLYCOLATE OXIDASE3, a Glycolate Oxidase Homolog of Yeast L-Lactate Cytochrome c Oxidoreductase, Supports L-Lactate Oxidation in Roots of Arabidopsis
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DOI：
10.1104/pp.15.01003
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发表时间：
2015-10-01
期刊：
影响因子：
7.4
通讯作者：
Maurino, Veronica G.
中科院分区：
文献类型：
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作者：
Engqvist, Martin K. M.;Schmitz, Jessica;Maurino, Veronica G.
在拟南芥（Arabidopsis thaliana）的根中，通过L-乳酸脱氢酶还原丙酮酸产生L-乳酸，但是该酶不能有效地催化逆反应。在这里，我们确定拟南芥乙醇酸氧化酶（GOX）旁系同源GOX 1，GOX 2和GOX 3作为推定的L-乳酸代谢酶的基础上，他们的同源性CYB 2，L-乳酸细胞色素c氧化还原酶从酵母酿酒酵母。我们发现GOX 3使用L-乳酸的效率与乙醇酸相似;相比之下，具有相似酶性质的光呼吸亚型GOX 1和GOX 2使用乙醇酸的效率比L-乳酸高得多。使GOX 3比GOX 1和GOX 2对L-乳酸更有效的关键因素是底物的Km低5至10倍。因此，只有GOX 3可以在低细胞内浓度下有效地代谢L-乳酸。同位素示踪实验以及使用GOX 3功能丧失和过表达植物的底物毒性测试表明，L-乳酸在体内由GOX 3代谢。此外，GOX 3挽救了缺乏CYB 2的酵母菌株的致死生长表型，该酵母菌株不能在L-乳酸盐作为唯一碳源上生长。GOX 3主要存在于根和成熟到老化的叶中，但在年轻的光合叶中基本上不存在，这表明它主要在异养组织而不是自养组织中起作用，至少在标准生长条件下是这样。在常氧条件下生长的植物根中，GOX 3功能的丧失诱导代谢重排，反映了缺氧条件下的野生型反应。因此，我们确定GOX 3作为在体内将L-乳酸代谢为丙酮酸的酶，并假设它可以确保在常氧下形成后维持低水平的L-乳酸。
In roots of Arabidopsis (Arabidopsis thaliana), L-lactate is generated by the reduction of pyruvate via L-lactate dehydrogenase, but this enzyme does not efficiently catalyze the reverse reaction. Here, we identify the Arabidopsis glycolate oxidase (GOX) paralogs GOX1, GOX2, and GOX3 as putative L-lactate-metabolizing enzymes based on their homology to CYB2, the L-lactate cytochrome c oxidoreductase from the yeast Saccharomyces cerevisiae. We found that GOX3 uses L-lactate with a similar efficiency to glycolate; in contrast, the photorespiratory isoforms GOX1 and GOX2, which share similar enzymatic properties, use glycolate with much higher efficiencies than L-lactate. The key factor making GOX3 more efficient with L-lactate than GOX1 and GOX2 is a 5- to 10-fold lower Km for the substrate. Consequently, only GOX3 can efficiently metabolize L-lactate at low intracellular concentrations. Isotope tracer experiments as well as substrate toxicity tests using GOX3 loss-of-function and overexpressor plants indicate that L-lactate is metabolized in vivo by GOX3. Moreover, GOX3 rescues the lethal growth phenotype of a yeast strain lacking CYB2, which cannot grow on L-lactate as a sole carbon source. GOX3 is predominantly present in roots and mature to aging leaves but is largely absent from young photosynthetic leaves, indicating that it plays a role predominantly in heterotrophic rather than autotrophic tissues, at least under standard growth conditions. In roots of plants grown under normoxic conditions, loss of function of GOX3 induces metabolic rearrangements that mirror wild-type responses under hypoxia. Thus, we identified GOX3 as the enzyme that metabolizes L-lactate to pyruvate in vivo and hypothesize that it may ensure the sustainment of low levels of L-lactate after its formation under normoxia.