Cheong J J, Hahn M G
Complex Carbohydrate Research Center, University of Georgia, Athens 30602.
Plant Cell. 1991 Feb;3(2):137-47. doi: 10.1105/tpc.3.2.137.
The presence of a specific binding site for a hepta-beta-glucoside elicitor of phytoalexin accumulation has been demonstrated in soybean microsomal membranes. A tyramine conjugate of the elicitor-active hepta-beta-glucoside was prepared and radiolabeled with 125I. The labeled hepta-beta-glucoside-tyramine conjugate was used as a ligand in binding assays with a total membrane fraction prepared from soybean roots. Binding of the radiolabeled hepta-beta-glucoside elicitor was saturable, reversible, and with an affinity (apparent Kd = 7.5 x 10(-10) M) comparable with the concentration of hepta-beta-glucoside required for biological activity. A single class of hepta-beta-glucoside binding sites was found. The binding site was inactivated by proteolysis and by heat treatment, suggesting that the binding site is a protein or glycoprotein. Competitive inhibition of binding of the radiolabeled hepta-beta-glucoside elicitor by a number of structurally related oligoglucosides demonstrated a direct correlation between the binding affinities and the elicitor activities of these oligoglucosides. Thus, the hepta-beta-glucoside-binding protein fulfills criteria expected of a bona fide receptor for the elicitor-active oligosaccharin.
在大豆微粒体膜中已证实存在一种可引发植物抗毒素积累的七-β-葡糖苷激发子的特异性结合位点。制备了激发子活性七-β-葡糖苷的酪胺缀合物并用125I进行放射性标记。将标记的七-β-葡糖苷-酪胺缀合物用作配体，与从大豆根制备的总膜部分进行结合测定。放射性标记的七-β-葡糖苷激发子的结合是可饱和的、可逆的，其亲和力（表观Kd = 7.5×10(-10) M）与生物活性所需的七-β-葡糖苷浓度相当。发现了一类单一的七-β-葡糖苷结合位点。该结合位点通过蛋白水解和热处理而失活，这表明该结合位点是一种蛋白质或糖蛋白。多种结构相关的寡糖苷对放射性标记的七-β-葡糖苷激发子结合的竞争性抑制表明，这些寡糖苷的结合亲和力与激发子活性之间存在直接相关性。因此，七-β-葡糖苷结合蛋白符合作为激发子活性寡糖素真正受体所期望的标准。
