Concanavalin A-reactive protein of rabbit thymocyte plasma membranes: analysis by crossed immune electrophoresis and sodium dodecylsulfate/polyacrylamide gel electrophoresis.

1. Thymocyte plasma membrane extracts, prepared with the non-ionic detergent Triton X-100, show 10 major protein components upon sodium dodecysulfate/polyacrylamide gel electrophoresis and at least 11 immunologic components upon crossed immune electrophoresis. 2. Concanavalin A reactive membrane proteins have been identified using crossed immune electrophoresis with receptor-ligand interaction. 3. These proteins are absorbed from Triton X-100-solubilized membranes onto immobilized concanavalin A. They are eluted in stepwise fashion, using increasing concentrations of alpha-methyl-d-glucoside, between 0.0004 M and 0.1 M. The predominant proteins eluted in each step are components with high electrophoretic mobility in crossed immune electrophoresis and are identical with a glycosylated component in sodium dodecysulfate/polyacrylamide gel electrophoresis with molecular weight of 55 000. 4. This component forms multimers in the presence of Triton X-100 which are not totally dissociated in sodium dodecylsulfate. 5. Neuramidase treatment followed by crossed immune electrophoresis of total plasma membrane isolates, as well as the purified glycoprotein fraction, indicates that the concanavalin A-reactive proteins are sialoglycoproteins. 6. Sodium dodecylsulfate component 5.1 comprises at least two different populations of glycoproteins (6 and 9) in crossed immune electrophoresis, one of which exclusively exhibits heterogenous carbohydrate antigenic sites (component 9). 7. Present data, taken together with previously published experiments, indicate that concanavalin A binding to intact thymocytes induces an increased turnover and release of the receptor protein(s).