Determination of Equilibrium and Kinetic Constants during Changes in the Ligand Concentration Due to Ligand--Receptor Interaction

K. G. Gurevich¹

¹Laboratory of Pathophysiology, Scientific Center for Mental Health, Russian Academy of Medical Sciences, Zagorodnoe Shosse 2, Moscow, 113152 Russia.

Submitted April 30, 1997.

---

Mathematical modeling was used to study ligand--receptor interaction (LRI) when the ligand and receptor concentrations are comparable. It is shown that for the exact definition of the kinetic constant of ligand--receptor association under these conditions it is necessary to take into account the receptor concentration and the receptor affinity. If the ligand concentration changes due to LRI, the analytic shape of graphs in Scatchard plots is not changed. However, with low ligand concentration equilibrium is reached later than with high ligand concentration. If with high ligand concentration equilibrium in the ligand--receptor system is reached and with low ligand concentration this equilibrium is not reached, a deviation of the graph in Scatchard plots from a straight line is observed. This can cause incorrect determination of the receptor affinity.

---

KEY WORDS: ligand--receptor interaction (LRI), discrimination of LRI models, Scatchard plots.

---