Differences in the binding of fluorescent concanavalin A to the surface membrane of normal and transformed cells

The binding of fluorescein-conjugated Concanavalin A to the cell surface has been studied in normal and transformed cells in interphase and mitosis. Binding to the cell surface was in the form of an incomplete ring of fluorescence, and the binding was inhibited by alpha-methyl-D-mannopyranoside. All the cells were fluorescent when treated with 25-250 mug/ml of fluorescent Concanavalin A. With 10 mug, the cells were all fluorescent after 30 min of binding, but after 0.5-5 min with 10 mug or 30 min with 1 or 2.5 mug, transformed interphase cells showed a higher percentage of cells with surface fluorescence than did normal interphase cells. Trypsinized normal and transformed interphase cells showed the same fluorescence. Binding with 2.5 mug at 4 degrees instead of at 24 degrees , gave a higher percentage of fluorescent cells with trypsinized than with untrypsinized transformed cells. Mitotic normal cells were similar to transformed interphase cells, whereas mitotic transformed cells were intermediate between normal and transformed interphase cells. The results indicate that the use of low concentrations of fluorescent Concanavalin A can show differences in surface fluorescence between normal and transformed, interphase and mitotic, and trypsinized and untrypsinized cells. It is suggested that the observed differences in fluorescence can be explained by differences in affinity of the lectin binding sites and/or differences in the clustering of sites.