Water receptor binding thermodynamics

Such structural models, however are hardly compatible with a lateral penetration of peptide ligands as required in a membrane-bound pathway c . he hormone/receptor recognition and binding process. Experimental evidences for such mechanism are difficult to produce, since in the partition equilibrium of hormones between the water and the lipid phase occupation of the receptor from the extracellular phase cannot be excluded. However, with an escape of the peptide ligands into the water phase and subsequent direct collision with the receptor binding site all the thermodynamic and conformational advantages of an accumulation at the membrane surface would be lost. 

Relative ligand binding in solution of different ligands Si and S2 to a receptor site or enzyme E can be estimated by the free energy perturbation method, using the principle of the thermodynamic cycle (Fig. 3), in which all processes are run with explicit inclusion of water. 

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