Binding (Molecular Biology)

Total binding BL is the number of ligand molecules that at any moment are in contact with (occupy sites on) the accessible surface of a protein molecule. It is related to preferential binding (as measured by equilibrium dialysis) by

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where BL and Bw are the numbers of ligand and water molecules, respectively, that are in contact with the protein surface.

When the interactions are weak, the ligand must be used at high concentration (eg, 1M sucrose, 3 M glycerol, 8 Murea). As a consequence, the total binding is not given by equilibrium dialysis, as the last term of Eq. (1) (binding of water) becomes significant. Total binding can be measured by nonthermodynamic techniques that respond to contacts between ligand molecules and protein [(1)]. Such techniques include calorimetric titration, which detects the heat of protein-ligand contact, or spectroscopic techniques (eg, fluorescence or uv absorbance) that detect spectral perturbations each time a ligand-protein contact is made. If the total hydration is known from other techniques, then total binding can be derived from dialysis equilibrium results by the application of Eq. (1).

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