Polymerization ofthe deoxy form ofsickle cell hemoglobin (Hb S; 136 Glu-*Val) involves both hydrophobic and electrostatic intermolecular contacts. These interactions drive the mutated molecules into long fibrous rods composed of seven pairs of strands. X-ray crystallography of Hb S and electron microscopy image reconstruction of the fibers have revealed the remarkable complementarity between one of the 186 valines ofeach molecule (the donor site) and an acceptor site at the EF corner of a neighboring tetramer. This interaction constitutes the major lateral contact between the two strands in a pair. To estimate the relative importance of this key hydrophobic contact in polymer formation we have generated a modeling of the donor-acceptor interaction shows that the presence of an isoleucine side chain at the donor site induces increased contacts with the receptor site and an increased buried surface area, in agreement with the higher hydrophobicity of the isoleucine residue. The agreement between the predicted and experimental differences in solubility suggests that the transfer of the 136 valine or isoleucine side chain from water to a hydrophobic environment is sufficient to explain the observations.Sickle cell hemoglobin (Hb S) has been the subject of intense interest because the replacement of the charged glutamate residue at the sixth position (A3) in the 13 chains by an uncharged valine leads to a drastic decrease in the solubility of the mutant Hb in its deoxy form. This drives the mutated molecules into long fibrous rods, distorting the erythrocytes into their characteristic sickle shape (1, 2). The thermodynamic behavior and kinetics of polymerization have been studied in detail (for recent reviews see refs. 3 and 4). The long rods in sickled cells possess a highly ordered structure involving 14 helical strands of the mutated tetramers. X-ray analyses of the structure of the polymers (5) as well as molecular imaging studies (6-8) have provided a clear understanding of the mechanisms responsible for the formation of the polymers, which include both hydrophobic and electrostatic interactions between the abnormal tetramers.Three other natural mutations at the 136 position have been described: Hb C (Glu--Lys), Hb Machida (Glu-oGln) (9), and Hb G-Makassar (Glu--Ala) (10). None of these Hbs exhibit gelling properties similar to those of Hb S (10, 11). These reports strongly suggested that the localized change in hydrophobicity at the surface of the A helix in the 13 chains of Hb S is a major determinant in producing the oxygenlinked decrease in solubility of deoxy Hb S, leading to the formation of the polymers. Structural analyses of the fibers and computer molecular modeling have revealed the remarkable complementarity between the side chain of the 136 valine of one tetramer with an acceptor site constituted by the 185 phenylalanine and ,B88 leucine side chains of another tetramer, thereby explaining the primary intermolecular interaction in Hb S fibers. The solubility of the Hb S tetramers may be furth...

Increased homotropic allosteric effect, while maintaining normal heterotropic effects, was observed in hemoglobin Loire. The oxygen binding curves, at equilibrium, and the kinetic measurements demonstrated that the substitution of a88(F9) Ala for a Ser results in increased oxygen affinity and decreased ns0 value. The function of the residues involved in the Bohr effect or in the regulation by 2,3-bisphosphoglycerate is not altered. The effects of bezafibrate, which binds specifically to the a chains, was similar to that observed in Hb A. The functional properties of Hb Loire may be explained by a slight displacement of some key residues of the Cterminal region of the a chain destabilizing the T structure.

High-performance liquid chromatography allows one to perform effective and rapid separations on microquantities of material. The miniaturization of the techniques led to new approaches involving iso-electric focusing (IEF) of immobilized pH gradient IEF for haemoglobin preparation, successive enzymic hy-drolyses for isolating abnormal peptides and amino acid composition determination after precolumn derivati-zation