DISTRIBUTION AND MOBILITY OF LECTINS WITH DIFFERENT CARBOHYDRATE-BINDING SPECIFICITIES ON L CELL PLASMA MEMBRANES AS REVEALED BY IMMUNO-FERRITIN TECHNIQUES

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DivisiFerritin-conjugated lectins were utilized for L cells as cytochemical stains for sugar residues in the complex carbohydrates of the cell membranes. Concanavalin A, Ricinus communis toxin, and Bauhinia purpurea hemagglutinin were coupled to ferritin with glutaraldehyde and purified by affinity chromatography. On fixed L cell plasma membranes, all of these ferritinconjugated lectins were uniformly distributed. The number of binding sites of these lectins on L cells was determined as 1.4×10⁶ for concanavalin A, 7.7×10⁶ for Ricinus communis toxin, and 0.2×10⁶ for Bauhinia purpurea hemagglutinin, from binding experiments with 131I-labeled lectins. On unfixed L cell plasma membranes, ferritin-conjugated concanavalin A became unevenly clustered at a low temperature (4°C). A small proportion of ferritinconjugated Ricinus communis toxin clustered, but ferritin-conjugated Bauhinia purpurea hemagglutinin did not cluster under the same conditions. Incubation at 37°C for 30 minutes, after the binding of ferritin-conjugated concanavalin A and Ricinus communis toxin, induced invagination of the plasma membranes, accompanied by internalization of the bound ferritin-conjugates.