Abstract
We have investigated the properties of β-galactosyltransferase (GalT) involved in the synthesis of the sugar portion of arabinogalactan-proteins whose basic structure comprises a β-(1->3)-galactan, branched with consecutive (1->6)-linked β-Gal residues, to which α-L-Ara and uronosyl residues are attached.
The activity of GalT was assayed by a reaction mixture containing a microsomal fraction prepared from etiolated soybean hypocotyls, UDP-Gal, and various galactooligosaccharides. Resulting Gal transfer products were derivatized with p-aminobenzoic acid ethyl ester (ABEE) and analyzed on HPLC.
The GalT catalyzed incorporation of Gal onto β-(1->3)-galactotriose as an acceptor through β-(1->6)-linkages, producing a branched tetrasaccharide, β-Gal-(1->3)[β-Gal-(1->6)]-β-Gal-(1->3)-Gal. The GalT appeared to prefer the formation of single β-(1->6)-linked Gal branches on the linear β-(1->3)-galactan chains. The GalT also transferred Gal onto β-(1->6)-galactotriose, producing β-(1->6)-galactotetraose. These results indicate that the enzyme involves in the synthesis of β-(1->3)(1->6)-galactan framework in AGPs.
