A study on concanavalin A binding to human erythrocytes.

Interactions of concanavalin A with human erythrocytes were studied using 125I-labelled concanavalin A and a centrifugal technique with dibutyl phthalate which permitted complete separation of bound and free concanavalin A. Binding of 125I-labelled concanavalin A to human erythrocytes was dependent on cell concentration, pH and temperature. Specificity of binding was confirmed by inhibition and dissociation studies with sugars and native concanavalin A. Positive cooperative binding of concanavalin A to human erythrocytes was observed at low concanavalin A concentrations (less than I microgram/ml) in both buffers studied. Positive cooperativity at higher concanavalin A concentrations (more than 100 microgram/ml) was seen in Tris-Hepes buffer but not in phosphate-buffered saline. Consistent with this cooperative effect was the observation that although dissociation of 125I-labelled concanavalin A from the erythrocytes was complete in the presence of 1 mg/ml of the native lectin, release was inhibited by low concentrations (1 microgram/ml). A comparison of concanavalin A binding with hemagglutination studies suggests that the amount of concanavalin A bound determines the rate of erythrocyte agglutination and the size of the aggregates formed.