Oxyhemoglobins

Hemoglobin (Hb) transports O2 from the Inngs to the tissnes of the body. At high pressures in the lungs, O2 combines with the iron atoms of hemoglobin, and is released into the body tissnes at low pressures. 

Hemoglobin has a molecular weight of -64500 and contains four (formally Fe(II)) iron atoms. Each of these atoms is coordinated to four nitrogen atoms of porphyrin, and to the nitrogen atom of a proximal histidine group. This bonding is shown in structure (31), 

Chapter 18 Transition Metal Complexes with CO, N2, NO and O2 Ligands 

To account for the diamagnetism of oxyhemoglobin, in 1936 Pauling and Coryell suggested that an S = 0 spin excited state with valence-bond structme (33) 

By delocalizing lone-pair electrons from the Fe and 0 of structures (35) and (36) into vacant bonding Fe-O or 0-0 orbitals, we reduce the magnitude of the atomic formal charges, and obtain increased-valence structures (37) arrd (38)16-20 

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Oxygen solubility Oxygen tents Oxygen transfer Oxygen transfer rate Oxygen transport Oxyhalide Oxyhemoglobin... 

In addition to COg, Cl and BPG also bind better to deoxyhemoglobin than to oxyhemoglobin, causing a shift in equilibrium in favor of Og release. These various effects are demonstrated by the shift in the oxygen saturation curves for Hb in the presence of one or more of these substances (Figure 15.35). Note that the Og-binding curve for Hb + BPG + COg fits that of whole blood very well. 

The sixth coordination position of Fe2+ in heme is occupied by a water molecule that can be replaced reversibly by oxygen to give a derivative known as oxyhemoglobin, which has the bright red color characteristic of arterial blood. 

Unfortunately, hemoglobin forms a complex with carbon monoxide that is considerably more stable than oxyhemoglobin. The equilibrium constant for the reaction... 

Oxyhemoglobin is red, and hemoglobin is blue. Use Le CMtelier s principle to explain why venous blood is blue and arterial blood is bright red. 

Lungs saturated with oxygen so the shift is to oxyhemoglobin formation. Tissues low in oxygen, so in venal blood, the shift is to hemoglobin formation. 

Oxides of nitrogen vapor la 86 11 -Oxoanderosterone lb 78 11 -Oxolanostenyl acetate la 62 Oxomemazine lb 354 17-Oxosteroids lb 78,79 Oxprenolol la 299 lb 268 Oxycodeinone lb 280 Oxydemeton methyl lb 164,165 Oxyhemoglobin, dipole moment la 97 Oxymorphone lb 280 Oxypertin lb 354 Oxytetracycline lb 271... 

Matthew, JB Hanania, GIH Gurd, ERN, Electrostatic Effects in Hemoglobin Hydrogen Ion Equilibria in Human Deoxy- and Oxyhemoglobin A, Biochemistry 18, 1919, 1979. 

Orttung, WH, Interpretation of the Titration Curve of Oxyhemoglobin. Detailed Consideration of Coulomb Interactions at Low Ionic Strength, Journal of the American Chemical Society 91, 162, 1969. 

C20-0111. Oxyhemoglobin is bright red, but deoxyhemoglobin is blue. In both cases the iron is in the +2 oxidation state. Give a detailed explanation for the difference in color. How would you test your hypothesis Based on your explanation, what color would you predict for a sample of blood that is saturated with carbon monoxide ... 

Hemoglobin Is a large complex protein molecule the atomic model of oxyhemoglobin at 2.8 a resolution has been reported In 1968 by Perutz and coworkers, and a similar model of deoxy-hemoglobin In 1970 (1,2). The molecule Is a spheroid, approx-... 

G. "Three-dimensional Fourier Synthesis of Horse Oxyhemoglobin at 2.8 A Resolution (II) The Atomic Model". Nature (1968), 219, 131. 

At the moment, only three in vitro studies have been performed on Bfx metabolic behavior, hi one case, it has been shown that Bfxs are able to be reduced by oxyhemoglobin to the corresponding o-nitroaniline derivatives (Scheme 5) [237]. hi the reaction between compoimd 135 and oxyhemoglobin compound 136 was generated as secondary product resulting from both nitrile hydrolysis and deoxygenation. This study indicates that blood is a possible site for metabolism of Bfxs with the consequent methemoglobinemia. 

Describe the physiological significance of the steep and plateau portions of the oxyhemoglobin dissociation curve... 

The P02 of blood is the major factor determining the amount of oxygen chemically combined with hemoglobin, or the percent of hemoglobin saturation. The relationship between these two variables is illustrated graphically by the oxyhemoglobin dissociation curve (see Figure 17.6). This relationship is not... 

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