Impact of oxidative stress on ascorbate biosynthesis in Chlamydomonas via regulation of the VTC2 gene encoding a GDP-L-galactose phosphorylase
(2012) Journal of Biological Chemistry — Vol. 287, n° 17, p. 14234-14245 (2012)
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- The L-galactose (Smirnoff-Wheeler) pathway represents the major route to L-ascorbic acid (vitamin C) biosynthesis in higher plants. Arabidopsis thaliana VTC2 and its paralogue VTC5 function as GDP-L-galactose phosphorylases converting GDP-L-galactose to L-galactose-1-P, thus catalyzing the first committed step in the biosynthesis of L-ascorbate. Here we report that the L-galactose pathway of ascorbate biosynthesis described in higher plants is conserved in green algae. The Chlamydomonas reinhardtii genome encodes all the enzymes required for vitaminC biosynthesis via the L-galactose pathway. We have characterized recombinant C. reinhardtii VTC2 as an active GDP-L-galactose phosphorylase. C. reinhardtii cells exposed to oxidative stressshow increased VTC2 mRNA and L-ascorbate levels. Genes encoding enzymatic components of the ascorbate-glutathione system (e.g. ascorbate peroxidase, manganese superoxide dismutase, and dehydroascorbate reductase) are also up-regulated in response to increased oxidative stress.Theseresults indicate that C. reinhardtii VTC2, like its plant homologs, is a highly regulated enzyme in ascorbate biosynthesis in green algae and that, together with the ascorbate recycling system, the L-galactose pathway represents the major route for providing protective levels of ascorbate in oxidatively stressed algal cells. © 2012 by The American Society for Biochemistry and Molecular Biology, Inc.
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Urzica, E. I., Adler, L. N., Page, M. D., Linster, C., Arbing, M. A., Casero, D., Pellegrini, M., Merchant, S. S., & Clarke, S. G. (2012). Impact of oxidative stress on ascorbate biosynthesis in Chlamydomonas via regulation of the VTC2 gene encoding a GDP-L-galactose phosphorylase. Journal of Biological Chemistry, 287(17), 14234-14245. https://doi.org/10.1074/jbc.M112.341982 (Original work published 2012)