Binding constant
The binding constant is a special case of the equilibrium constant K. It is associated with the binding and unbinding reaction of receptor (R) and ligand (L) molecules, which is formalized as:
The reaction is characterized by the on-rate constant kon and the off-rate constant koff, which have units of mol s and s, respectively. In equilibrium, the forward binding transition R + L → RL should be balanced by the backward unbinding transition RL → R + L. That is,