LIGAND BINDING - TUTORIAL #7 answer 7-2: separate analysis of each X binding isotherm       The analysis you suggested is acceptable but is not the best in the statistical sense; after reading this page you may consider going back one step and check the other answer.       Each binding isotherm is fitted to the approximate partition equation:       [PX]/[P]tot = [X] / (X50 +[X]) that we derive from the previously obtained [PX]/[P]tot = [X]Ky / ([Y]Kx +[X]Ky). Under this approximation, X50 = Kx [Y]/Ky       Notice that, because of the assumption we made ([Y]>Ky) the above equation necessarily implies X50 > Kx. The vales of X50 thus obtained are plotted against [Y] and from linear regression we obtain the slope, which equals Kp = Kx / Ky. Back one step.