 The strength of complex formation in solution is related to the stability constants of complexes, however in case of large biomolecules, such as receptor-ligand pairs, their interaction is also dependent on other structural and thermodynamic properties of reactants plus their orientation and immobilization.There are several methods to investigate protein–protein interactions existing with differences in immobilization of each reactant in 2D or 3D orientation.The measured affinities are stored in public databases, such as the Ki Database and BindingDB.