Partial purification of Golgi-bound arabinosyltransferase and two isoforms of xylosyltransferase from French bean (Phaseolus vulgaris L.)

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Abstract
The purification of glycosyltransferases involved in wall matrix polysaccharide synthesis has been attempted. A number of activities readily demonstrated in isolated Golgi membranes are lost following detergent solubilization. However, solubilization releases pyrophosphorylases and phosphatases that hydrolyse the substrate in enzyme assays, whether UDP-glucose, -arabinose or -xylose is used. This hydrolysis, which cannot be completely inhibited, appears to be the major factor in the apparent loss of activity. Separation of this hydrolytic activity during further purification by ion-exchange and gel exclusion leads to recovery of glycosyltransferase activity. Thus two xylosyltransferases and one arabinosyltransferase could be partially purified. These appeared to be differentially expressed. The arabinosyltransferase of apparent M(r) 70,000 on size-exclusion chromatography was isolated from cells undergoing rapid growth and division. A xylosyltransferase of apparent M(r) 38,000 on size-exclusion chromatography was associated with cell expansion and primary wall synthesis. A second xylosyltransferase, which was purified to near homogeneity with M(r) 40,000, showed a peak of activity during the period of maximum secondary wall synthesis.