Horovitz A, Levitzki A
Department of Biological Chemistry, Hebrew University of Jerusalem, Israel.
Proc Natl Acad Sci U S A. 1987 Oct;84(19):6654-8. doi: 10.1073/pnas.84.19.6654.
Receptor-ligand dissociation constants are usually calculated from the displacement curve of a radioactively labeled ligand bound to the receptor. The formula used is restricted to cases in which the concentration of receptor is negligible compared to the concentration of both the displacing ligand and the radioactive ligand used. In this study, we rigorously derive a simple equation that can be used for calculating receptor-ligand dissociation constants for any set of experimental conditions. A linearized form of this equation provides a convenient plot from which the dissociation constant of the displacing ligand can be directly obtained. The plot is also a test for the competitive mode of binding. This exact equation now allows us to estimate the error incurred by the conventionally used equations. Similarly, we show that for competitive inhibition in enzymology, one can derive the analogous formula. Our new formula is free of the usual restrictions--namely, that the enzyme concentration is very small compared to the concentration of both the substrate and the inhibitor. It may therefore be applied to any set of experimental conditions.
受体-配体解离常数通常根据与受体结合的放射性标记配体的置换曲线来计算。所使用的公式仅限于受体浓度与置换配体和所用放射性配体的浓度相比可忽略不计的情况。在本研究中，我们严格推导了一个简单的方程，该方程可用于计算任何一组实验条件下的受体-配体解离常数。该方程的线性化形式提供了一个方便的图表，从中可以直接获得置换配体的解离常数。该图表也是对结合竞争模式的一种检验。这个精确的方程现在使我们能够估计传统使用的方程所产生的误差。同样，我们表明，对于酶学中的竞争性抑制，可以推导出类似的公式。我们的新公式没有通常的限制，即酶浓度与底物和抑制剂的浓度相比非常小。因此，它可以应用于任何一组实验条件。
