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 pectins or the glycoproteins arabinogalactan proteins and extensins contain arabinosyl residues. The arabinosyl substituents are thought to be incorporated into these wall polymers by the action of arabinosyltransferases using UDP-l-arabinose as the precursor. UDP-l-arabinose is not commercially available and therefore a procedure for generating UDP-l-arabinose was developed for use in studies on the biosynthesis of the arabinose-containing polymers. In this procedure UDP-d-xylose is incubated with an enzyme preparation from wheat germ and the nucleotide sugars in the reaction mixture are extracted. High-performance anion-exchange chromatography of the extract resolves two major UV-absorbing components: one corresponding to UDP-xylose and a second that elutes earlier. TLC analysis of collected and hydrolyzed fractions demonstrated the presence of l-arabinose in the early eluting fraction. Further analysis by NMR identified the compound as UDP-beta-l-arabinopyranose. The procedure reported here provides an efficient method for preparing either radioactive UDP-l-[(14)C]arabinose or nonradioactive UDP-l-arabinose and can also be used as an assay for UDP-xylose-4-epimerase activity. Copyright 2000 Academic Press.