PubMed Health⌕ Search

Biomedical subjects

B Magdoff-Fairchild

Publications and source records attributed to B Magdoff-Fairchild.

5 recordsLinked to original sources
PubMed1979

X-ray diffraction studies of fibers and crystals of deoxygenated sickle cell hemoglobin.

Paracrystalline fibers of deoxygenated sickle hemoglobin in erythrocytes or concentrated solutions exhibit a phase transformation to a fully crystalline state. X-ray diffraction patterns of the fiber and crystallites are similar except in two respects: the equatorial spacings of the fibers suggest that they pack into a square lattice with a = 220 A, whereas those of the crystals can be indexed on the basis of a net of 187 A by 54 A, and the second-order near-meridional reflections are strong on the fiber pattern but weak on that of the crystallites. The crystallites are isomorphous with single crystals grown in polyethylene glycol solution at pH 4.5 whole structure has been determined at near-atomic resolution (Wishner, B.C., Ward, K.B. Lattmen, E.E. & Lowve, W.E. (1975) J. Mol. Biol. 98, 179-194). Double filaments of molecules with an axial repeat of 64 A comprise the basic unit of both the crystal and fiber structures. Each filament of the pair is translated with respect to its neighbor by half a molecular diameter along the fiber axis. The two filaments are held together by contacts made by Val 6beta in the molecules of one strand with hydrophobic side chains of the molecule in the neighboring strand. This interaction is probably the cause of the aggregation of filaments into fibers that leads to the sickling of erythrocytes.

Crystallography↗
PubMed1977

Effect of 2, 3-diphosphoglycerate on the solubility of deoxy-sickle hemoglobin.

We have examined the effect of 2, 3-diphosphoglycerate (DPG) on the solubility of deoxy-sickle hemoglobin (deoxy-Hb S) under conditions such that concentration, pH, and osmolarity of deoxy-Hb S solutions approached physiological. The range of DPG/Hb molar ratios encompassed the extremes found for this ratio in erythrocytes from individuals with sickle cell anemia. After monomer-polyer equilibrium had been established, the phases were separated by centrifugation and assayed for concentrations of Hb and DPG. DPG had no effect on the solubility of deoxy-Hb S. Furthermore, at DPG/Hb molar ratios less than one, there was no preferential incorporation of deoxy-Hb S containing bound DPG into polymers. At DPG/Hb molar ratios greater than one, concentrations of free DPG in monomer and polymer phases were virtually identical. Thus, under the specified equilibrium conditions, DPG is not a determining factor in the polymerization of deoxy-Hb S.

Anemia, Sickle Cell↗
PubMed1976

Thermodynamic studies of polymerization of deoxygenated sickle cell hemoglobin.

Solubilities of deoxygenated sickle cell hemoglobin (deoxy-Hb S), at varying pH and temperature over a range of concentrations encompassing those found in erythrocytes, were measured. The technique involved ultracentrifugation, which gave values of the supernatant concentration and the mass of the sedimented material. The data establish that the solubility of doexy-Hb S is the saturation concentration and is independent of initial concentration. The mass of the pellet phase increases linearly with initial concentration. Moreover, the saturation concentration represents the critical concentration above which monomers are in equilibrium with polymers. These polymers are the putative cause of erythrocytes deformation associated with sickle cell anemia. The solubility-pH profiles of deoxy-Hb S at various temperatures, unlike those of other proteins, show no minima at the isoelectric pH but instead show a marked decrease in solubility below pH 7.0, indicating the predominance of polymerization over the expected increase in solubility. Deoxy-Hb S, within specified ranges of temperature and pH, possesses a negative temperature coefficient of solubility, a property characteristic of hydrophobic interactions. The saturation concentration is, however, temperature independent at conditions close to physiological. The enthalpy of polymerization (3.5 kcal/mol) is temperature independent from 6 degrees to 22 degrees for all pH values between 6.45 and 7.40. In the range of 22 degrees to 38 degrees, this parameter becomes less endothermic, having a value of 2.5 kcal/mol at pH 6.45 and a value of zero at pH 7.20. Such behavior of the system suggests a phase transition near 22 degreas. Within the range of conditions examined the polymerization is entropically driven.

Hemoglobin, Sickle↗