title: Cooperative binding of concanavalin A to thymocytes at 4 degrees C and micro-redistribution of concanavalin A receptors.
abstract: The mode of binding of 125I-labelled concanavalin A and succinyl-concanavalin A to rat thymocytes at 4 degrees C was investigated. Simultaneously, the free binding sites of the cell-bound lectin molecules were quantified by horseradish peroxidase binding. Concanavalin A showed cooperative binding while succinyl-concanavalin A did not. The number of molecules of concanavalin A bound to the cell surface when it was saturated was twice the number of molecules of succinyl-concanavalin A. We interpret these results as showing that the binding of native concanavalin A to thymocytes at 4 degrees C brings about a cooperative modification of the membrane which leads to appearance of new receptors. Divalent succinyl-concanavalin A has no such effect. Horseradish peroxidase binding to cell-bound lectin was shown to be related to the immobilization of membrane receptors; the more they are immobilized, the more receptor-associated lectin can bind horseradish peroxidase. This allowed us to establish that post-binding events, which we called micro-redistribution, occurred at 4 degrees C when either concanavalin A or succinyl-concanavalin A binds to cells. A cooperative restriction of the micromobility of cell receptors is produced by increasing concentrations of concanavalin A. Succinyl-concanavalin A does not restrict cell receptor mobility at any concentration tested. The results are discussed in terms of cell stimulation and cell agglutination.
mesh_terms: D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D003208:Concanavalin A / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D006735:Horseradish Peroxidase / Q000378:metabolism; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D008766:Methylmannosides / Q000494:pharmacology; D011485:Protein Binding; D051381:Rats; D011955:Receptors, Drug; D013386:Succinates; D013696:Temperature; D013950:Thymus Gland / Q000187:drug effects / Q000378:metabolism*
chemical_list: D008766:Methylmannosides; D011955:Receptors, Drug; D013386:Succinates; D003208:Concanavalin A; D006735:Horseradish Peroxidase