equilibrium constantmedical dictionary

<chemistry> The ratio of the reverse and forward rate constants for a reaction of the type:

A + B = AB

at equilibrium the equilibrium constant (K) equals the product of the concentrations of reactants divided by the concentration of product and has dimensions of concentration.

Kd = (concentration A.concentration B) / (concentration AB).

The affinity constant (Ka) is the reciprocal of the equilibrium constant.

Dimension: moles per litre. In general the concept of Kd is more readily understood than that of Ka, for example: in considering the conversion of A to AB by the binding of ligand B, the Kd = B when A = AB. Thus Kd is equal to the ligand concentration which produces half maximal conversion (response).

(10 Jan 1998)