A quantitative analysis of excluded‐site effects for highly cooperative binding systems

Binding isotherms can provide quantitive information regarding the stability of a molecular complex. Theorectical studies in recent years have been directed to systems in which a single ligand can exclude more than one polymer site (excluded‐site effect). This system has minium of thre parameters to describe the binding data: the intrinsic binding constant, B ; the remote‐neighbor cooperative paramaters, σ q and the number of excluded sites, q . It is suggested in the present communication that precise values for these three parameters can be obtained by utilizing the characteristics of two forms of data representation: θ vs ln m and θ/ m vs θ, where θ is the degree of saturation (0⩽θ⩽1) and m is the molality of free ligand. The matrix generation method is used to obtain empirical equations relating the midpoint location and slope at the midpoint of the θ vs ln m plot to the three molecular parameters. A modified Scatchard theory is also presented for highly cooperative systems, which results in an expression relaing the maximum in the θ/ m vs θ plot to the molecular parameters σ q and q , thus providing the third equation for the three unknown parameters. The novel method f analysis is illustrated with the AMP‐poly( L ‐arginine) and oligocytidylate–T7 DNA sstems.