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Plant Physiol. 2006 Jul;141(3):851-7. Epub 2006 May 12.

Early steps in the biosynthesis of NAD in Arabidopsis start with aspartate and occur in the plastid.

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  • 1Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara 630-0192, Japan.


NAD is a ubiquitous coenzyme involved in oxidation-reduction reactions and is synthesized by way of quinolinate. Animals and some bacteria synthesize quinolinate from tryptophan, whereas other bacteria synthesize quinolinate from aspartate (Asp) using L-Asp oxidase and quinolinate synthase. We show here that Arabidopsis (Arabidopsis thaliana) uses the Asp-to-quinolinate pathway. The Arabidopsis L-Asp oxidase or quinolinate synthase gene complemented the Escherichia coli mutant defective in the corresponding gene, and T-DNA-based disruption of either of these genes, as well as of the gene coding for the enzyme quinolinate phosphoribosyltransferase, was embryo lethal. An analysis of functional green fluorescent protein-fused constructs and in vitro assays of uptake into isolated chloroplasts demonstrated that these three enzymes are located in the plastid.

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