Hemoglobins oxygen equilibria

Hemoglobin (Hgb) binds with oxygen molecules that enter your bloodstream, producing oxygenated hemoglobin (Hgb(02)4). The equilibrium of Hgb and O2 is represented as follows. 

In the mountains The equilibrium reacts to the stress of thin mountain air by producing oxygen at an increased rate. The shift to the left releases oxygen molecules in your lungs, leaving less oxygenated hemoglobin in your blood. 

Figure 9-9. Oxygen-binding equilibrium curves for (a) cell-free hemoglobin in pH 7.4 aqueous solution at 37 °C, (b) Co picketfence-Ofrn in the membrane state at 25 C, (c) Co picketfence-Olm in toluene solution at 25 C, (d) CoOEP-OIm in CH2CI2 at -15 °C, and (e) Co picketfence-OPy in toluene solution at 25 C. Inset UV-Vis absorption spectral change of the CoOEP-OIm complex in CH2CI2 at -15 C in response to oxygen partial pressure from 0 to 760 mmHg.

As blood flows out of the lungs and into muscles and organs where oxygen concentrations have been depleted (because muscles and organs use oxygen), the equilibrium shifts to the left— hemoglobin releases oxygen ... 

Figure 4 Oxygen-binding equilibrium curves for the aqueous solution of (a) liposomal lipid-heme, (b) hemoglobin in red blood cell, (c) hemoglobin (cell-free), (d) cobalt-poly(ethyleneimine), and (e) myoglobin at pH 7.4, at 37 C po2, atmospheric oxygen partial pressure.

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 ... 

In hemoglobin M, histidine F8 (His F8) has been replaced by tyrosine. The iron of HbM forms a tight ionic complex with the phenolate anion of tyrosine that stabilizes the Fc3 form. In a-chain hemoglobin M variants, the R-T equilibrium favors the T state. Oxygen affinity is reduced, and the Bohr effect is absent. P Ghain hemoglobin M variants exhibit R-T switching, and the Bohr effect is therefore present. 

The binding and release of oxygen by hemoglobin can be represented as a ligand-exchange equilibrium at the sixth coordination site on the Fe ion. Each of the four polypeptide chains of hemoglobin contains one heme unit, so... 

Fig. 8. Oxygen equilibrium curves of caiman and horse hemoglobin with and without C02. C0] = 40Torr, 25°C, I = 0.2 M, pH 7,2 for caiman (60), pH 7.4 for horse (104).

Papoulis, A., 1965, Probability, Random Variables, and Stochastic Processes, McGraw-Hill, New York. Pauling, L., 1935, The oxygen equilibrium of hemoglobin and its structural interpretation, Proc. Natl. 

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