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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

Identification of a Mung Bean Arabinofuranosyltransferase That Transfers Arabinofuranosyl Residues onto (1, 5)-Linked -L-Arabino-Oligosaccharides¹

Forestry and Forest Products Research Institute, Tsukuba, Ibaraki 305–8687, Japan (T.K., T.I.); and National Food Research Institute, Tsukuba, Ibaraki 305–8642, Japan (H.O., M.O.-K., S.K.)

Arabinofuranosyltransferase activity was identified in Golgi membranes obtained from mung bean (Vigna radiata) hypocotyls. The enzyme transfers the arabinofuranosyl (Araf) residue from UDP--L-arabinofuranose to exogenous (1, 5)-linked -L-arabino-oligosaccharides labeled at their reducing ends with 2-aminobenzamide. The transferred residue was shown, using ¹H-nuclear magnetic resonance spectroscopy and -L-arabinofuranosidase treatment, to be -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 V_max 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.

The author responsible for the distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Tadashi Ishii (tishii{at}ffpri.affrc.go.jp).

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.106.080309.

^* Corresponding author; e-mail tishii{at}ffpri.affrc.go.jp; fax 81–29–874–3720.

Received March 13, 2006; returned for revision April 26, 2006; accepted April 26, 2006.

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