Binding of two molecules of 4-methylumbelliferyl galactose or 4-methylumbelliferyl N-acetylgalactosamine to the B chains of ricin and Ricinus communis agglutinin and to purified ricin B chain.

The binding of 4-methylumbelliferyl galactose and 4-methylumbelliferyl N-acetylgalactosamine to ricin, Ricinus communis agglutinin, and ricin B chain was studied by fluorescence polarization and equilibrium dialysis. The binding of [3H]galactose to ricin was also studied by equilibrium dialysis. The results were consistent with binding of 2 mol of ligand to ricin (which contains 1 A chain and 1 B chain) and ricin B chain and 4 mol of ligand to the agglutinin (which contains 2 A chains and 2 B chains). There was no evidence for interaction between the 2 sites on any of the B chains.