Binding site noninteracting

Fig. 3. Ligand binding behavior of a hypothetical protein exhibiting a unit Hill coefficient of (hh = 1). Such behavior would be expected (a) for the case of a protein with only a single binding site or (b) for the case of an oligomeric protein containing n independent and noninteracting binding sites.

Figure 1. Ligand binding to a lattice of noninteracting binding sites.

Myer and Schellman (469) have measured the binding of 5 -AMP by equilibrium dialysis. The data appeared to indicate two noninteracting binding sites characterized by a single dissociation constant. At pH 7.5 in 0.05 M tris buffer the value of the constant was 3mM at 30°. AH for the association reaction was —4.2 kcal/mole and AS = —2.0 eu. There is no evidence for two equivalent binding sites for any other nucleotide. 

Question If the hemoglobin tetramer had four identical noninteracting binding sites, what relative values would the intrinsic binding constants have ... 

The data below describe the binding of ligand L to its receptor R (100 /association constant and the number of noninteracting equivalent sites. 

Equilibrium-dialysis experiments revealed two 2-acetamido-2-deoxy-D-galactose binding-sites per molecule of soybean agglutinin.544 This value was confirmed by gel filtration of the lectin on a column equilibrated with a radioactive ligand. The noninteracting, identical sites exhibited an association constant of Ka = 3.0 X 104 liter.mole-1 for this 2-acetamido-2-deoxyhexose. 

The first case of multiple-site bindings involves a biomacromolecule with n equivalent sites (each of the n sites has the same affinity, K for the ligand) and the binding is non-cooperative (each of the n sites is noninteracting/independent). Consideration of the stereochemistry of the bounded A for n equivalent sites suggests that there are... 

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