Figure 2. Biochemical properties of xylan xylosyltransferase activity in microsomes from rice stems. The xylosyltransferase activity was assayed by incubating microsomes with the UDP-[¹⁴C]-xylose donor and the Xyl₄ acceptor for 30 min unless otherwise indicated. The activity (CPM) was measured by the transfer of the radiolabeled xylosyl group onto the acceptor. All assays were repeated twice and the data are means ± SE of assays from 3 independently isolated microsomes. (A) Dependence of the xylosyltransferase activity on the Xyl₄ acceptor concentration. (B) Time course of the transfer of the radiolabeled xylosyl residues onto the acceptor by the xylosyltransferase activity. (C) The xylosyltransferase activity is protein concentration-dependent.