Impact of oxidative stress on ascorbate biosynthesis in Chlamydomonas via regulation of the VTC2 gene encoding a GDP-L-galactose phosphorylase.
J Biol Chem
; 287(17): 14234-45, 2012 Apr 20.
Article
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| MEDLINE
| ID: mdl-22393048
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 vitamin C 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 stress show 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. These results 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.
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1
Banco de datos:
MEDLINE
Asunto principal:
Regulación de la Expresión Génica
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Chlamydomonas reinhardtii
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Monoéster Fosfórico Hidrolasas
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Proteínas de Arabidopsis
Idioma:
En
Revista:
J Biol Chem
Año:
2012
Tipo del documento:
Article
País de afiliación:
Estados Unidos