PURIFICATION AND SPECIFICITY OF BETA-1,2-XYLOSYLTRANSFERASE, AN ENZYME THAT CONTRIBUTES TO THE ALLERGENICITY OF SOME PLANT-PROTEINS

The enzyme that transfers D-xylose from UDP-xylose to the beta-linked mannose of plant N-linked oligosaccharides was purified about 51,000-f old to apparent homogeneity from soybean microsomes. On SDS gels, two proteins of 56 and 59 kDa were detected and both were labeled to the s ame extent by the photoaffinity label, 5-N-3-UDP-[P-32]xylose. Labelin g of both proteins was inhibited by cold UDP-xylose, but not by UDP-gl ucose. The amount of 5-N-3-UDP-[P-32]xylose that bound to the two prot ein bands was greatly increased in the presence of oligosaccharide acc epters. The best acceptor for xylose transfer and for stimulation of U DP-xylose binding was GlcNAc(2)Man(3)GlcNAc(2)-T, but GlcNAc(1)Man(3)G lcNAc(2), with the GlcNAc on the 3-branch, was also a good acceptor an d a good stimulator. A number of other N-linked oligosaccharides were poor accepters, especially those with galactose units at the nonreduci ng termini, Many of the properties of this enzyme have been described, and the product of the reaction of UDP-xylose and GlcNAc(2)Man(3)(Glc NAc)(2) was characterized as GlcNAc beta 1, 2Man alpha 1,6(GlcNAc beta 1,2Man alpha 1,3) (Xyl beta 1,2)Man beta 1,4GlcNA c(2)-T by chemical and NMR methods.