Binding oxygen

The most conspicuous use of iron in biological systems is in our blood, where the erythrocytes are filled with the oxygen-binding protein hemoglobin. The red color of blood is due to the iron atom bound to the heme group in hemoglobin. Similar heme-bound iron atoms are present in a number of proteins involved in electron-transfer reactions, notably cytochromes. A chemically more sophisticated use of iron is found in an enzyme, ribo nucleotide reductase, that catalyzes the conversion of ribonucleotides to deoxyribonucleotides, an important step in the synthesis of the building blocks of DNA. 

Mb Sperm whale myoglobin, an oxygen-binding protein 153 amino acid residues. Note that Mb lacks cysteine. 

We can determine quantitatively the physiological significance of the sigmoid nature of the hemoglobin oxygen-binding curve, or, in other words, the biological importance of cooperativity. The equation... 

The experimentally observed oxygen-binding curve for Hb does not fit the graph given in Figure A15.3 exactly. If we generalize Equation (A15.10) by replacing the exponent 4 by n, we can write the equation as... 

The value Pso has been defined above for myoglobin as the pO that gives 50% saturation of the oxygen-binding protein with oxygen. Noting that at 50% saturation, F= (1 — F), then we have from Equation (A15.13). 

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 ... 

Thermodynamics of oxygen binding in natural and synthetic dioxygen complexes. E. C. Nieder-hoffer, J. H. Timmons and A. E. Martell, Chem. Rev., 1984, 84,137-203 (599). 

Allcock, H. R., Neenan, T. X., and Boso, B., Synthesis, oxygen-binding behavior, and Mossbauer spectroscopy of covalently-bound polyphosphaene heme complexes, Inorg. Chem.. 

Histidines F8 E7 Perform Unique Roles in Oxygen Binding... 

The potential of relevance for competitive adsorption of water may shift upon alloying Pt. The calculated ratio of water to oxygen binding energies at the UHV... 

Greeley J, Nprskov JK. 2005. A general scheme for the estimation of oxygen binding energies on binary transition metal surface alloys. Surf Sci 592 104-111. 

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