Effects of Phagocytosis and Colchicine on the Distribution of Lectin-Binding Sites on Cell Surfaces

The effect of phagocytosis on lectin binding to plasma membranes of polymorphonuclear leukocytes was examined. The specific activities of binding sites of concanavalin A and Ricinus communis agglutinin (defined as mug of lectin bound per 100 mug of membrane protein) were measured on isolated membranes; they decreased in parallel with phagocytosis. Our data suggest that this removal occurs by concentration of binding sites into internalized membrane. Colchicine and vinblastine, which did not inhibit phagocytosis, prevented the selective removal of lectin-binding sites from the surface. It was also shown that at 37 degrees lectins induce their own internalization. This property was used to define operationally three classes of lectin receptors, one of which is most extensively removed from plasma membrane during phagocytosis. Based on other morphological studies in which it is shown that before phagocytosis the surface distribution of concanavalin-binding sites is random, it is inferred that phagocytosis alters surface topography by inducing the selective movement of binding sites into membrane undergoing internalization and that colchicine-sensitive proteins are essential for this imposed topographical reorganization.