A particulate enzyme preparation from suspension-cultured bean (Phaseolus vulgaris) was shown to incorporate xylose from UDP-D-[U14C] xylose, fucose from GDP-D-[U14C]fucose, and glucose from UDP-D-glucose, into polysaccharide. The xylosyltransferase was dependent upon the presence of UDP-glucose, and was stimulated and apparently protected by GDP-glucose and GDP-mannose, though neither was able to replace UDP-glucose as a glycosyl donor. The product of the reaction was identified as xyloglucan by analysis of the products of enzyme breakdown and acid hydrolysis, and by a cellulose binding study. Molecular weight determination following proteinase K digestion indicated that the nascent xyloglucan is closely attached to protein. Pre-incubation of the enzyme with UDP-glucose stimulated incorporated from UDP-D-[U14C] xylose suggesting the simultaneous presence of both nucleotides is not necessary for growth of the polysaccharide. The fucosyltransferase was not dependent upon the presence of other sugar nucleotides, though some stimulation by UDP-galactose occurred. Fucose was transferred from GDP-D-[U14C] fucose into a polysaccharide with the characteristics of xyloglucan, as indicated by enzyme and acid hydrolysis. Transfer of glucose from UDP-D-[U14C] glucose showed no stimulation by UDP-xylose and was slightly inhibited at higher concentrations of UDP-xylose. The product of the transfer was susceptible to beta1-3 glucanase digestion and did not show enzyme hydrolysis products characteristic of xyloglucan
