Oxygen binding constants

In the concerted model, the first binding of substrate increases the affinity of the other active sites, but further bindings have no effect. This doesn t contradict the haemoglobin/oxygen binding constants presented earlier, as the increased affinities at ever increasing oxygen concentrations could be due to the increased proportion of relaxed form, rather than to individual increases in each protein molecule (Fig. 6.16). 

The oxygen binding constant log Kq2 was defined for the equilibrium, according to the formula ... 

Thermodynamically it would be expected that a ligand may not have identical affinity for both receptor conformations. This was an assumption in early formulations of conformational selection. For example, differential affinity for protein conformations was proposed for oxygen binding to hemoglobin [17] and for choline derivatives and nicotinic receptors [18]. Furthermore, assume that these conformations exist in an equilibrium defined by an allosteric constant L (defined as [Ra]/[R-i]) and that a ligand [A] has affinity for both conformations defined by equilibrium association constants Ka and aKa, respectively, for the inactive and active states ... 

The binding constants are also influenced by the number of ion-dipole interactions present involving the metal and the ether oxygen donors. As the ring size increases, so will the number of available dipoles this effect will be superimposed (and may dominate) the metal-ion binding pattern along a series of crowns. 

Cellular oxygen is bound by myoglobin molecules that store it until it is required for metabolic action, where upon they release it to other acceptors. Hemoglobin has a additional function, however, and that is to carry CO2 back to the lungs this is done by certain amino acid side chains, and the heme groups are not directly involved. Because the circumstances under which Hb and Mb are required to bind and release O2 are very different, the two substances have quite different binding constants as a function of O2 partial pressure (Fig.). 

As noted earlier, the similarities between H+ and alkali metal cations have led to the use of the former as a probe in biological studies, including studies with various macrocydic ligands, especially those with oxygen donor atoms. The thallium(I) cryptates behave kinetically like the potassium compounds, and the binding constants to 18-crown-6 have been measured by 205T1 NMR methods.347 Several Tl1 compounds with crown ethers (L) have been prepared in... 

Binding Constants of Protons to Dianions of Dicarboxylic Acids Thermodynamic Functions for Oxygenation of Hemoglobin A Few Well-Known Structural Domains... 

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