Interactions of lectins with CHO cell surface membranes. I. Competition studies indicate concanavalin a and WGA bind to discrete populations of sites.

The binding of radioiodinated lectins to the CHO cell surface was measured for the following affinity purified plant agglutinins; concanavalin A, wheat germ agglutinin, Ricinus agglutinins (I, II) pea agglutinin, peanut agglutinin, and Bandeiria simpliciafolia agglutinin (BSLI). The number of binding sites at saturation ranged from 6 x 10(5) for BSL I to 5 x 10(7) for pea and Ricinus. Affinity constants calculated by the Steck-Wallach procedure ranged form 2 x 10(5) m(-1) for pea lectin to 4.5 x 10(5) M(-1) L for peanut lectin. Competition studies between homologous and heterologous radiolabeled and unlabeled lectins indicated that homologous unlabeled lectin could fully block binding of radiolabeled lectin. For heterologous pairs, a variety of results were observed. Of particular interest is the finding that concanavalin A and wheat germ agglutinin mutually failed to compete for binding indicating that these two lectins bind to distinct, nonoverlapping populations of surface sites. This finding suggests that the binding sites for WGA and Con A reside, for the most part, on discrete populations of membrane molecules; this concept is further validated in a companion paper in the upcoming issue of this journal (Schwartz et al., 1982).