Hemoglobin tetramers determination

Calculate the fractional saturation YT of the tetramer of human hemoglobin with molecular oxygen using the equilibrium constants determined by Mills, Johnson, and Akers (1976) at 21.5 °C, 1 bar, pH 7.4, [Cl"] = 0.2 M and 0.2 M ionic strength. Make the calculation with the Adair equation and also by using the binding polymomial YT. 

At specified concentration of molecular oxygen, the five forms of hemoglobin are pseudoisomers, and they have the same further transformed Gibbs energy of formation at equilibrium. The further transformed thermodynamic properties of the tetramer can be calculated from experimental measurements of the fractional saturation, but in order to interpret experimental data, it is necessary to provide for the partial dissociation of tetramer 02 Bz into dimers a/3 (3). Seven apparent equilibrium constants are required to describe experimental data, and it is shown that all seven can be determined using limiting forms (4). 

There are two major molecular variants of thalassemia, the a- and jS-type. In each type, the genetically determined block interferes with biosynthesis of either the a- or jS-chain. j8-Thalassemia is the most common and is associated with a reduction in A (aj ) hemoglobin and an increase in A2 hemoglobin. An a4 tetramer does not usually appear in the blood it is too unstable. In contrast, no A2 is formed in a-thalassemia, and tetramers of either the y-hemoglobin Bart (74) or j8-hemoglobin H P4) may appear in the blood. 

The hemoglobins of erythrocytes (molecular weight 68,000) are tetramers with one heme per polypeptide the association of the four subunits results in a spheroid approximately 71 X 54 X 52 A. The position of the hemes, at least for horse hemoglobin has been determined by electron spin resonance (2H) the hemes are not parallel to each other. One pair lies in the a, b plane of the crystal while the other pair is tilted 13° above and below the plane. The three dimensional structure of hemoglobin to a resolution of 6 A has been achieved (215). 

---