Single-site binding model

Figure 5.9 Typical ITC data for binding of a trisaccharide inhibitor (tri-/V-acetyl-glucosamine tri-NAG) to hen egg white lysozyme, in 0.1 mol dm ethanoate buffer, pH 5. Each exothermic heat pulse (upperpanel) corresponds to injection of 10 nL (0.01 cm ) of tri-NAG (0.45 mmol dm ) into the protein solution (36 nmol dm ). Integrated heat data (lower panel) constitute a differential binding curve that may be fit to a standard single-site binding model to give, in this instance, the stoichiometry of binding (number ol binding sites), A/=0.99 binding affinity.

For simple processes in which multiple metals bind to a single ligand = 1 and iEL = 1 (AEE1 = 0) and hence the extended site binding model reduces back the basic site binding model. Figure 10.17 shows... 

Let us consider the fixation of a bidentate ligand to a single metal as depicted in Figure 84. The first step simply corresponds to a standard intermolecular binding process modeled by a statistical factor and an absolute intermolecular affinity according to the site-binding model... 

In order to measure any constant, we need an equation that relates this constant to variables that maybe determined by experiment. For a single-site, single-affinity binding model, there is a relatively simple way of deriving such an equation. If we define total concentration of receptor [R]o according to... 

The fitting of ITC data requires a model to calculate the change in complex concentration for each incremental increase in ligand concentration. For example, for single-site binding with a binding constant K, the concentration of complex after the ith injection is given by ... 

It is surprising that data on natural particles can be fitted over a range of concentrations (representative of those encountered in natural waters) on the basis of a "single-site" surface complex formation model. Apparently similar types of binding groups are predominant and of importance in these particles. 

Finally, we consider the effects on recognition and binding of single site replacements [34] of the individual charged residues which have been emphasized in molecular modeling studies. These residues include Lys (18, 32, 77) in cytochrome c and Asp (37, 79, 217) in ccp. 

One of our main assumptions in the derivation of the Langmuir model [and implicitly made by Langmuir himself (1918)] is that the binding process does not affect the distribution of states of the adsorbent molecules. Removal of this assumption has a profound effect on the form of the BI of systems with more than a single site. 

Substituting these expressions into the equations above yields a new expression that enables the interaction kinetics to be readily modeled for single-site, reversible binding between a protein and a single ligand ... 

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