The dissociation rate in chemistry, biochemistry, and pharmacology is the rate or speed at which a ligand dissociates from a protein, for instance, a receptor. It is an important factor in the binding affinity and intrinsic activity (efficacy) of a ligand at a receptor. The dissociation rate for a particular substrate can be applied to enzyme kinetics, including the Michaelis-Menten model. Substrate dissociation rate contributes to how large or small the enzyme velocity will be. In the Michaelis-Menten model, the enzyme binds to the substrate yielding an enzyme substrate complex, which can either go backwards by dissociating or go forward by forming a product. The dissociation rate constant is defined using K.
The Michaelis-Menten constant is denoted by K and is represented by the equation K= (K + K)/ K. The rates that the enzyme binds and dissociates from the substrate are represented by K and K respectively. K is also defined as the substrate concentration at which enzymatic velocity reaches half of its maximal rate. The tighter a ligand binds to a substrate, the lower the dissociation rate will be. K and K are proportional, thus at higher levels of dissociation, the Michaelis-Menten constant will be larger.