LIGAND BINDING - TUTORIAL #7 answer 7-3: Global fitting of the equation to the exerimental data       Very good! Global fitting of the equation to the exerimental data is the statistically soundest procedure you can apply to this problem. It requires some skill with numerical data analysis and access to a suitable package, e.g. Matlab or Octave; if you have the necessary competence you can write down a dedicated program and compile it (e.g. in Fortran, C or Pascal).       We demonstrated in the preceding step of our analysis that the fraction of X-bound ligand binding sites according to the reaction scheme: PY + X <==> P + X + Y <==> PX + Y       is:       [PX]/[P]tot = [X]Ky / (KxKy + [Y]Kx +[X]Ky)       The above equation is a two variabel function, that allows us to calculate [PX]/[P]tot for every couple [X],[Y]. If we fit the above equation to the experimental data presented in the left panel of the figure shown at the beginning of this tutorial we obtain the following values: Kx = 1 mM; Ky = 0.3 mM; the partition constant of the protein between the two ligands results: Kp = 3.33.       proceed to the conclusion of this tutorial. Back one step.