Abstract
We have investigated β-galactosyltransferase (GalTase) involved in the synthesis of arabinogalactan-proteins whose basic carbohydrate structure comprises a β-(1→3)-galactan, branched with consecutive (1→6)-linked β-Galp residues, to which α-L-Araf residues are attached through (1→3)-linkages.
The enzymatic reaction was carried out in a mixture composed of a microsome fraction prepared from etiolated soybean hypocotyls, UDP-[14C]Gal, and β-(1→3)-galactan as an acceptor at 25°. The Gal transfer occurred maximally at pH 5.7 in the presence of 15 mM Mn2+ and 0.75% Triton X-100 (specific activity about 500 pmol/min/mg protein). Digestion of the radiolabeled product with exo-β-(1→3)-galactanase released radiolabeled β-1,6-galactobiose as the main product, indicating preferential transfer of Gal groups onto the β-(1→3)-galactan chains through β-(1→6)-linkages, creating branching points. β-1,3-Galactooligomers served as acceptor while β-1,6-oligomers were inactive.
