Molecular heterogeneity of the concanavalin A tetramer: effects on binding to human red blood cells.

We have found that the distribution of the three main monomer species found in tetrameric concanavalin A was approximately 73% type A monomer (27,000 MW); 4% type B monomer (14,000 MW); and 23% type C monomer (12,000 MW). When this tetrameric concanavalin A was bound to human erythrocytes and the monomer distribution of the bound concanavalin A was examined, we found that it resembled that of the concanavalin A used in the binding reaction. However, when competing sugars were used, either to inhibit the binding of concanavalin A or to remove previously-bound lectin, examination of cell-bound monomer distribution revealed that there was a significant increase in type C monomers and a simultaneous decrease in type A monomers. The shifts in monomer distribution varied depending on experimental conditions and the particular competing inhibitor employed. These findings were taken to indicate that not all concanavalin A cell surface interactions are identical and that quantitative methods are available for studying this phenomenon.