Hemoglobin tetramer

Hemoglobins bind four molecules of Oj per tetramer, one per heme. A molecule of Oj binds to a hemoglobin tetramer more readily if other Oj molecules are already bound (Figure 6-4). Termed cooperative binding, this phenomenon permits hemoglobin to maximize both the quantity of O2 loaded at the PO2 of the lungs and the quantity of O2 released at the PO2 of the peripheral tissues. Gooperative interactions, an exclusive property of multimeric proteins, are critically important to aerobic life. 

The subunit composition of hemoglobin tetramers undergoes complex changes during development. The... 

Within the a2 2 hemoglobin tetramer, the a and /3 subunits (made up of 141 and 146 amino acid residues, respectively) can be thought of as two a/S-dimeric units that are symmetrically positioned about a central cavity ... 

Human carbonic anhydrase II, found primarily in the erythrocyte, is the prototypical member of the family of carbonic anhydrases and has been extensively reviewed (Pocker and Sarkanen, 1978 Lindskog, 1983, 1986 Silverman and Lindskog, 1988). Within the erythrocyte carbonic anhydrase II hydrates CO2 to form bicarbonate ion plus a proton via tandem chemical processes (Silverman and Lindskog, 1988) (Scheme 2). Most of the carbon dioxide generated during the process of respiration requires this carbonic anhydrase Il-catalyzed event for transport out of the cell. The resultant protons of CO2 hydration are taken up by His-146)8, His-122a, and the amino terminus of the a subunits of the hemoglobin tetramer. As a reference. Scheme 3 outlines the interconversions... 

A. B-Globin gene deletions in the p-tnalassemias. B. Hemoglobin tetramers formed in p-thalassemias. 

Hemoglobin tetramers tend to stay tightly associated but some dissociation of oxyhemoglobin into dimers does occur (fQ = 7 x 105 M).137/138 Deoxyhemoglobin is about 40,000 times more tightly associated. All of... 

When HbS is deoxygenated it tends to "crystallize" in red blood cells, which contain 33% by weight hemoglobin. The crystallization (actually gel formation) distorts the cells into a sickle shape and these distorted corpuscles are easily destroyed, leading to anemia. The introduction of the hydrophobic valine residue in Hb S at position 6 near the end of the molecule helps form a new bonding domain by which the hemoglobin tetramers associate to form long semicrystalline microfilamentous arrays. 3 6 s... 

Table 7.1 Standard Transformed Gibbs Energy of Formation AfG ° and Standard Further Transformed Gibbs Energies of Formation AfG ° of Hemoglobin Tetramer at 21.5JC, 1 bar, pH 7.4, [Cl ] = 0.2 M, and 0.2 M Ionic Strength...

An alternative way of viewing the concept of extrinsic binding constants is as follows. The experimentally measured binding constant for each site of a polymeric protein, or enzyme, will depend on the number of available sites on each molecule e.g., for the hemoglobin tetramer the first binding reaction is... 

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

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