Numerical analysis of binding studies: a direct procedure avoiding the pitfalls of a Scatchard analysis of equilibrium data for unknown binding models.

It is shown on theoretical grounds that the straightforward analysis of binding data according to Scatchard may lead to erroneous results, especially when more complicated binding schemes are involved. We have demonstrated this point by presenting Scatchard plots with slight variation of experimental parameters. These inherent difficulties of Scatchard analyses can be avoided by applying a direct procedure. We have developed a program, which compares the measured quantity and the theoretical value directly and which considers the following binding models: (i) independent equivalent binding of n ligands; (ii) independent unequivalent binding of 2 ligands; (iii) positive or negative cooperative binding of 2 ligands. Other binding schemes can easily be implemented. We have used this procedure for the evaluation of equilibrium data on the complex formation of tRNA-Tyr and tyrolyl tRNA synthetase from E. coli in terms of different binding models.