Biosynthesis of xyloglucan in suspension-cultured soybean cells. An assay method for xyloglucan xylosyltransferase and attempted synthesis of xyloglucan from UDP-D-xylose.

Hydrolysis of the total non-cellulosic 14C-polysaccharides from soybean cell wall with carbohydrate hydrolases of an Aspergillus oryzae enzyme preparation yielded 14C-monosaccharides and [14C]isoprimeverose (6-O-alpha-D-xylopyranosyl-D-glucopyranose) in which all of the xylosyl residues of the xyloglucan were recovered. Based on this finding, an assay method for the activity of xyloglucan xylosyltransferase was developed. When UDP-[14C]xylose was incubated with a particulate enzyme fraction from soybean cells, radioactive polymers were synthesized. On digestion with the A. oryzae enzyme preparation, the product gave 14C-monosaccharides and [14C]isoprimeverose. This result suggests that the activity of xyloglucan xylosyltransferase can be distinguished from other polysaccharide synthase activities.