Cooperative binding of concanavalin A to thymocyte membrane vesicles augments uptake of alpha aminoisobutyrate.

(1) Membrane vesicles from rabbit thymocytes accumulate alpha-aminoisobutyrate in the presence of 0.1 M NaCl. Uptake is 1/2 maximal after about 2 min and reaches a plateau value (61 pmoles/mg protein) after 30 min. (2) Up to 25 mug concanavalin A/ml, binding of the lectin describes a sigmoid curve indicative of a cooperative process. (3) At lectin concentrations up to 8 mug/ml, lectin binding enhances the uptake of alpha-aminoisobutyrate (maximally 30%).