Abstract
Erythroascorbic acid (eAsA) seen in budding yeast has been supposed to be synthesized by the successive reactions of NADP-dependent arabinose dehydrogenase (ARA) and arabinonolactone oxidase (ALO1). Here, we found NAD-dependent ARA and identified its corresponding gene.
First, we showed the presence of NAD-dependent ARA activity with a higher affinity against arabinose than NADP-dependent ARA in protein extracts of yeasts. Next, we found that the uncharacterized YMR041c gene is the ortholog of plant galactose dehydrogenase, and that its recombinant protein possesses NAD-dependent ARA activity. YMR041c coupled with ALO1 produced eAsA in vitro. Moreover, the gene disruptant of YMR041c abolished the increase in intracellular eAsA by arabinose feeding, while wild-type and NADP-dependent ARA disruptant showed more than 10-fold. These results clearly shows the similarity between the biosynthetic pathway of eAsA in yeasts and that of ascorbic acid in higher plants also in terms of enzyme structures.
