A xylosyltransferase involved in the synthesis of a protein-associated xyloglucan in suspension-cultured dwarf-French-bean (Phaseolus vulgaris) cells and its interaction with a glucosyltransferase.

A particulate enzyme preparation made from suspension-cultured dwarf-French-bean (Phaseolus vulgaris) cv. Canadian Wonder cells was shown to incorporate xylose from UDP-D-[14C]xylose into polysaccharide. The reaction was dependent upon the presence of UDP-D-glucose and was stimulated, and apparently protected, by GDP-D-glucose and GDP-D-mannose, though neither was able to replace UDP-D-glucose as a glycosyl donor. The product of the reaction was identified as xyloglucan by analysis of products of enzyme breakdown and acid hydrolysis. Mr determination after proteinase K digestion indicated that the nascent xyloglucan is closely associated with protein. Preincubation of the enzyme with UDP-D-glucose stimulated incorporation from UDP-D-[14C]xylose, suggesting an 'imprecise' mechanism of biosynthesis, as defined by Waldron & Brett [(1985) in Biochemistry of Plant Cell Walls (Brett, C. T. & Hillman, J. R., eds.) (SEB Semin. Ser. 28), pp. 79-97, Cambridge University Press, Cambridge].