Effects of Phagocytosis and Colchicine on the Distribution of Lectin-Binding

The effect of phagocytosis on lectin bind- ing to plasma membranes of polymorphonuclear leuko- cytes was examined. The specific activities of binding sites of concanavalin A and Ricinus communis agglutinin (defined as gg of lectin bound per 100 pg 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 lectins induce their own internaliza- tion. 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 con- canavalin-binding sites is random, it is inferred that phagocytosis alters surface topography by inducing the selective movement of binding sites into membrane under- going internalization and that colchicine-sensitive pro- teins are essential for this imposed topographical re- organization.