Abstract
Arabinose is a quantitatively major component of numerous plant polysaccharides. In these polysaccharides the arabinosyl residues exit predominantly in the α-L-arabinofurasoyl (α-L-Araf) form. UDP-Β-L-arabinopyranose (UDP-Arap) has been used for in vitro biosynthesis of arabinose-containing plant polysaccharides. But the structure of the incorporated arabinosyl residues were not fully characterized. We studied transfer of arabinose residues from UDP-Arap to exogenous galactooligosaccharides using solubilized microsomal fraction from mung bean (Vigna radiate).
The enzymatically formed mono-arabinose-containing galactooligosaccharides were analyzed by MS and NMR. The incorporated Ara is α-L-arabinopyranosyl and the Ara is linked at 0-4 of non-reducing Gal residues of the oligosaccharides. Galactooligosaccharides are acceptors for galactosyltransferase (GalT), but the arabinose-containing oligosaccharides are not acceptors for GalT, indicating that the non-reducing Ara residue of galactooligosaccharides terminates galactan chain elongation.
