[New physical interpretation of S-shaped curves: competition between various types of binding of ligands with DNA]. / Novaia fizicheskaia interpretatsiia S-obraznogo vida krivykh: konkurentsiia mezhdu raznymi tipami sviazyvaniia liganda s DNK.

ABSTRACT

In studies of interactions of ligands with nucleic acid molecules, S-shaped curves are often obtained. In this work we show that the sigmoidal shape of the curves is due to a competition of ligand molecules for DNA binding sites. If a ligand that binds to DNA can form two types of complexes with the binding constants K1 and K2 and binding site sizes L1 and L2, respectively, then in the event that K1 < K2 and L1 < L2, the dependence of the concentration of complexes of the first type on the concentration of the ligand added to solution can be S-shaped.