PLANT PHYSIOLOGY , Vol 110, Issue 2 665-673, Copyright © 1996 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
[alpha]-L-Fucosyltransferases from Radish Primary Roots
H. Misawa, Y. Tsumuraya, Y. Kaneko and Y. Hashimoto
Department of Biochemistry (H.M., Y.T., Y.H.) and Department of Regulation Biology (Y.K.), Faculty of Science, Saitama University, 255 Shimo-okubo, Urawa 338, Japan
A novel [alpha]-L-fucosyltransferase capable of transferring L-fucose
(L-Fuc) from GDP-L-Fuc to the O-2 of [alpha]-L-arabinofuranosyl residue
(GDP-L-Fuc:[alpha]-L-arabinofuranoside 2-[alpha]-L-fucosyltransferase) has
been found in the microsomal fraction of primary roots from 6-d-old radish
(Raphanus sativus L.) seedlings. Enzyme activity was measured
fluorometrically at 25[deg]C using a pyridylaminated trisaccharide,
L-arabinofuranosylf[alpha](1->3)D-galactopyranosyl[beta](1->6)D-galac
tose (AraGalGal-PA) as the acceptor. This enzyme found in the microsomal
fraction is maximally active at pH 6.8 and requires 0.1% (w/v) Zwittergent
3-16 and 5 mM Mn2+. Chemical and enzymatic analyses of fucosylated
AraGalGal-PA confirmed the attachment of L-Fuc to the L-arabinofuranosyl
(L-Araf) residue at O-2 by [alpha]-glycosidic linkage. Radiolabeling was
used to assay L-Fuc transfer to L-Araf-containing galacto-oligomers and
tamarind xyloglucan. The enzyme specific for the L-Araf residue undergoes
development- and organ-specific expression in root tissue, whereas the
L-Fuc transfer to tamarind xyloglucan can be detected in microsomal
fractions from various organs in developing radish plants. Enzyme assays of
membranes fractionated from microsomal fractions revealed that two distinct
[alpha]-L-fucosyltransferases with different acceptor specificity are
associated with Golgi membranes from primary roots, whereas hypocotyl Golgi
membranes completely lack the enzyme specific for the L-Araf residue.
