Amako Katsumi, Fujita Kazuyo, Shimohata Taka-aki, Hasegawa Etsuko, Kishimoto Ritsuko, Goda Kiyoshi
Faculty of Nutrition, Kobe Gakuin University, 518 Arise, Kobe, Hyogo 651-2180, Japan.
FEBS Lett. 2006 Nov 27;580(27):6428-34. doi: 10.1016/j.febslet.2006.10.058. Epub 2006 Nov 3.
Erythroascorbic acid (eAsA) is a five-carbon analog of ascorbic acid, and it is synthesized from D-arabinose by D-arabinose dehydrogenase (ARA) and D-arabinono-gamma-lactone oxidase. We found an NAD+-specific ARA activity which is operative under submillimolar level of d-arabinose in the extracts of Saccharomyces cerevisiae. The hypothetical protein encoded by YMR041c showed a significant homology to a l-galactose dehydrogenase which plays in plant ascorbic acid biosynthesis, and we named it as Ara2p. Recombinant Ara2p showed NAD+-specific ARA activity with Km=0.78 mM to d-arabinose, which is 200-fold lower than that for the conventional NADP+-specific ARA, Ara1p. Gene disruptant of ARA2 lost entire NAD+-specific ARA activity and the conspicuous increase in intracellular eAsA by exogenous d-arabinose feeding, while the double knockout mutant of ARA1 and ARA2 still retained measurable amount of eAsA. It demonstrates that Ara2p, not Ara1p, mainly contributes to the production of eAsA from d-arabinose in S. cerevisiae.
赤藓糖型抗坏血酸（eAsA）是抗坏血酸的一种五碳类似物，它由D -阿拉伯糖通过D -阿拉伯糖脱氢酶（ARA）和D -阿拉伯糖酸-γ-内酯氧化酶合成。我们在酿酒酵母提取物中发现了一种NAD⁺特异性的ARA活性，该活性在亚毫摩尔水平的D -阿拉伯糖条件下起作用。由YMR041c编码的假定蛋白与在植物抗坏血酸生物合成中起作用的L -半乳糖脱氢酶具有显著同源性，我们将其命名为Ara2p。重组Ara2p表现出对D -阿拉伯糖的NAD⁺特异性ARA活性，Km = 0.78 mM，这比传统的NADP⁺特异性ARA即Ara1p低200倍。ARA2基因敲除突变体失去了全部NAD⁺特异性ARA活性以及通过外源添加D -阿拉伯糖导致的细胞内eAsA的显著增加，而ARA1和ARA2的双敲除突变体仍保留可测量量的eAsA。这表明在酿酒酵母中，主要是Ara2p而非Ara1p有助于从D -阿拉伯糖生产eAsA。
