Enzymatic synthesis and purification of uridine diphospho-beta-L-arabinopyranose, a substrate for the biosynthesis of plant polysaccharides

Many plant cell wall components such as the polysaccharides xylans and pect ins or the glycoproteins arabinogalactan proteins and extensins contain ara binosyl residues. The arabinosyl substituents are thought to be incorporate d into these wall polymers by the action of arabinosyltransferases using UD P-L-arabinose as the precursor. UDP-L-arabinose is not commercially availab le and therefore a procedure for generating UDP-L-arabinose was developed f or use in studies on the biosynthesis of the arabinose-containing polymers. In this procedure UDP-D-xylose is incubated with an enzyme preparation fro m wheat germ and the nucleotide sugars in the reaction mixture are extracte d. High-performance anion-exchange chromatography of the extract resolves t wo major UV-absorbing components: one corresponding to UDP-xylose and a sec ond that elutes earlier. TLC analysis of collected and hydrolyzed fractions demonstrated the presence of L-arabinose in the early eluting fraction. Fu rther analysis by NMR identified the compound as UDP-beta-L-arabinopyranose . The procedure reported here provides an efficient method for preparing ei ther radioactive UDP-L-[C-14]arabinose or nonradioactive UDP-L-arabinose an d can also be used as an assay for UDP-xylose-4-epimerase activity. (C) 200 0 Academic press.