Equilibrium dialysis and cell binding studies on Bandeiraea simplicifolia lectin

Equilibrium dialysis studies on the binding of the blood group B-specific Bandeiraea simplicifolia lectin to methyl alpha-D-galactopyranoside demonstrated the existence of one carbohydrate binding site per subunit for the tetrameric protein, with an intrinsic association constant of 8.6 x 10(4) (M) (-1) at 2 degrees and 3.3 x 10(4) (M)(-1) at 20 degrees. These values correspond to a free energy of binding, ΔG(0') (pH 7.2), of -6.21 kcal/mol and-6.06 kcal/mol at 2 degrees and 20 degrees, respectively. The sites appeared homogeneous and noninteracting. B. simplicifolia lectin receptor sites per human B erythrocyte varied from 0.72 x 10(5) to 1.34 x 10(5) with an apparent association constant of 1.1 x 10(7) (M)(-1) to 2.9 x 10(7) (M)(-l). The binding characteristics of B. simplicifolia lectin are compared to other purified lectins.