Abstract
Arabinose is a major component of numerous plant polysaccharides, and it exists predominantly in the α-L-arabinofuranosyl (α-L-Araf) form. However, small amounts of arabinopyranosyl (Arap) residues were detected. In in vitro studies of the biosynthesis of arabinose-containing polysaccharides UDP-arabinopyranose (UDP-Arap) has been used as the glycosyl donor. However, the enzymatically formed products and acceptor substrates have not been well characterized. We studied arabinosyltransferase (AraT) activity and the structure of the products formed when UDP-Arap and UDP-arabinofuranose (UDP-Araf) are reacted with fluorescent-labeled arabinofurano-oligosaccharides in the presence of mung bean microsomal membranes. Our data show that the membranes contain AraT activity that transfers a single arabinopyranosyl residue to O-3 of the non-reducing terminal Araf of the oligosaccharides when UDP-Arap is the glycosyl donor. A small amount of Araf residues are incorporated to O-5 of the non-reducing terminal Araf of the oligosaccharides, in addition to incorporation of arabinopyranosyl residues when UDP-Araf is used.
