CALCULATING THE DISSOCIATION-CONSTANT OF AN UNLABELED COMPOUND FROM THE CONCENTRATION REQUIRED TO DISPLACE RADIOLABEL BINDING BY 50-PERCENT

  • 1 January 1982
    • journal article
    • research article
    • Vol. 8  (3) , 163-172
Abstract
To determine the binding dissociation constant (KI) of a nonradiolabeled compound, the method of Cheng and Prusoff has been widely employed. The technique involves monitoring the competitive displacement from receptors of a radiolabeled compound with a known Kd by a nonradiolabeled compound. The concentration of nonradiolabeled compound which displaces 50% of the radiolabel, the IC50, is used to estimate its KI, with correction for competition with the radiolabel. The error of this method is small if the concentration of receptor is much less than Kd and Ki, constraints which are sometimes difficult to meet. Formulae are derived from which KI can be calculated from IC50 with no constraints on the receptor concentration.

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