Competitive interactions of drugs with their targets: a computerized improvement of Dixon's algorithm.

Many drugs are competitive and reversible enzyme inhibitors. When the target enzyme kinetics follows the Michaelis-Menten equation, the enzyme affinity of the inhibitor is characterized by a single parameter: the Ki value. This parameter is usually determined via Dixon's procedure: (i). the rate of reaction (V) is measured in the presence of a few concentrations of the inhibitor (I); (ii.) 1/V versus I gives a straight line, which allows a graphic determination of the inhibitory constants, or better via a least-square fit the linear regression. The introduction of appropriate weighting factors in the linear regression may improve the accuracy of the Ki determinations.