[alpha]-L-Fucosyltransferases from Radish Primary Roots

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 degrees C using a pyridylaminated trisaccharide, L-arabinofuranosylf alpha(1-->3)D-galactopyranosyl beta(1-->6)D-galactose (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.