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It is associated with the binding and unbinding reaction of receptor (R) and ligand (L) molecules, which is formalized as: R + L ⇌ RL. The reaction is characterized by the on-rate constant k on and the off-rate constant k off, which have units of M −1 s −1 and s −1, respectively. In equilibrium, the forward binding transition R + L → ...
When each receptor has a single ligand binding site, the system is described by [] + [] [] with an on-rate (k on) and off-rate (k off) related to the dissociation constant through K d =k off /k on. When the system equilibrates,
The definition can easily be extended to include any number of reagents. The reagents need not always be a metal and a ligand but can be any species which form a complex. Stability constants defined in this way, are association constants. This can lead to some confusion as pK a values are dissociation constants. In general purpose computer ...
Receptor–ligand binding kinetics also involves the on- and off-rates of binding. A main goal of receptor–ligand kinetics is to determine the concentrations of the various kinetic species (i.e., the states of the receptor and ligand) at all times, from a given set of initial concentrations and a given set of rate constants.
The dissociation rate constant is defined using K off. [2] The Michaelis-Menten constant is denoted by K m and is represented by the equation K m = (K off + K cat)/ K on [definition needed]. The rates that the enzyme binds and dissociates from the substrate are represented by K on and K off respectively.
In these applications, terms such as stability constant, formation constant, binding constant, affinity constant, association constant and dissociation constant are used. In biochemistry, it is common to give units for binding constants, which serve to define the concentration units used when the constant's value was determined.
In chemistry, biochemistry, and pharmacology, a dissociation constant (K D) is a specific type of equilibrium constant that measures the propensity of a larger object to separate (dissociate) reversibly into smaller components, as when a complex falls apart into its component molecules, or when a salt splits up into its component ions.
When determining the stability constants of metal-ligand complexes, it is common practice to fix ligand protonation constants at values that have been determined using data obtained from metal-free solutions. Hydrolysis constants of metal ions are usually fixed at values which were obtained using ligand-free solutions.