Differential ligand binding to OBPs. A. Binding curve of OBPs to 1-NPN, showing dissociation constants in the range of 1 to 5 μM which allowed for an accurate evaluation of the affinities towards other ligands in competitive binding assays. Purified recombinant proteins at the concentration of 2 μM in Tris buffer were titrated with increasing amounts of the fluorescent probe. B, C and D: Competition curves for the seven ligands with the highest affinities for OBP16, OBP18 and OBP21 respectively using the procedure described in Figure 7 and in the Methods section.