title: A specific, high-affinity binding site for the hepta-beta-glucoside elicitor exists in soybean membranes.
abstract: 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.
authors.affiliation: Complex Carbohydrate Research Center, University of Georgia, Athens 30602.
authors.forename: J J
authors.initials: JJ
authors.lastname: Cheong
authors.forename: M G
authors.initials: MG
authors.lastname: Hahn
mesh_terms: D001665:Binding Sites; D001667:Binding, Competitive; D002240:Carbohydrate Sequence; D005936:Glucans / Q000737:chemistry / Q000378:metabolism*; D005960:Glucosides / Q000737:chemistry / Q000378:metabolism; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D008861:Microsomes / Q000378:metabolism*; D008969:Molecular Sequence Data; D010936:Plant Extracts / Q000096:biosynthesis; D011402:Pronase / Q000378:metabolism; D012717:Sesquiterpenes; D013025:Glycine max / Q000378:metabolism*; D013729:Terpenes; D014439:Tyramine; D000094162:Phytoalexins
chemical_list: D005936:Glucans; D005960:Glucosides; D010936:Plant Extracts; D012717:Sesquiterpenes; D013729:Terpenes; C073685:heptaglucoside; D011402:Pronase; D014439:Tyramine; D000094162:Phytoalexins