Identification of a mung bean arabinofuranosyltransferase that transfers arabinofuranosyl residues onto (1,5)-linked α-L-arabino-oligosaccharides

Abstract

Arabinofuranosyltransferase activity was identified in Golgi membranes obtained from mung bean (Vigna radiata) hypocotyls. The enzyme transfers the arabinofuranosyl (Araf) residue from UDP-β-L-arabinofuranose to exogenous (1,5)-linked α-L-arabino-oligosaccharides labeled at their reducing ends with 2-aminobenzamide. The transferred residue was shown, using 1H-nuclear magnetic resonance spectroscopy and α-L- arabinofuranosidase treatment, to be α-L-Araf and to be linked to O-5 of the nonreducing terminal Araf residue of the acceptor oligosaccharide. The enzyme was nonprocessive because only a single Araf residue was added to the acceptor molecule. Arabino-oligosaccharides with a degree of polymerization between 3 and 8 were acceptor substrates. The 2-aminobenzamide-labeled arabino-tetra- and pentasaccharides were the most effective acceptor substrates analyzed. The enzyme has a pH optimum between 6.5 and 7.0 and its activity is stimulated by Mn2+ and Co2+ ions. The apparent K m and Vmax values of the arabinofuranosyltransferase for UDP-arabinofuranose are 243 μM and 243 pmol min-1 mg protein -1, respectively. The highest enzyme activity was detected in the elongating regions of mung bean hypocotyls. The data show that UDP-arabinofuranose is the donor molecule for the generation of arabino-oligosaccharides composed of Araf residues. © 2006 American Society of Plant Biologists.