In 1949, the discovery that sickle hemoglobin (α2 βS2) has an abnormal electrophoretic mobility prompted Linus Pauling and his colleagues to christen sickle cell anemia “a molecular disease.”1 The ensuing five decades have produced a wealth of information on the mechanisms by which a single base substitution in the gene encoding the human β-globin subunit, with the resulting replacement of β6 glutamic acid by valine, leads to the protean and devastating clinical manifestations of sickle cell disease. Until recently there was a disappointing lag in the application of this knowledge to the design of safe and effective . . .

Pathogenesis and Treatment of Sickle Cell Disease

Genetic, biochemical, and clinical features of chronic granulomatous disease

Oxygen Carriers (“Blood Substitutes”)Raison d'Etre, Chemistry, and Some Physiology Blut ist ein ganz besondrer Saft1

Publisher Summary The chapter describes the understanding of the physics and physical chemistry of sickle cell hemoglobin polymerization in solutions and in red cells. The polymerization of sickle cell hemoglobin has probably become the best understood of all protein self-assembly systems. The structure of the hemoglobin S molecule, the structure of the various aggregated forms of hemoglobin S, and the structural analysis of the polymers are discussed in the chapter. The chapter discusses the thermodynamics of hemoglobin S polymerization, and includes a description of the nonideal behavior of concentrated hemoglobin S solutions and the effects of physiologically relevant variables, especially oxygen, and the presence of non-S hemoglobins on the polymerization process. Understanding the polymerization process is not only important for understanding the pathophysiology of sickle cell disease, but is critical to the major problem of developing a specific therapy that could be used in the treatment of patients. The kinetic and thermodynamic studies have played a major role by providing relevant and sensitive assays for potential therapeutic agents. The results of the thermodynamic and kinetic studies of solutions are used to explain various properties of cells, including morphological and rheological properties.

Sickle cell hemoglobin polymerization.

The effect of excluded volume on the thermodynamic activity of globular macromolecules and macromolecular complexes in solution is studied in the hard-particle approximation. Activity coefficients are calculated as a function of the fraction of total volume occupied by macromolecules using relations obtained from scaled particle and lattice models. Significant and readily observable effects are predicted to occur as the fraction of volume occupied by globular macromolecules increases, including the following: (i) Compact quasi-spherical macromolecular conformations become increasingly energetically favored over extended anisometric conformations. (ii) Self- and heteroassociation processes are enhanced, particularly those leading to the formation of compact quasi-spherical aggregates. (iii) Depending upon the details of the reaction mechanism, the rate of an enzyme-catalyzed reaction may monotonically decrease, go through a maximum, or exhibit more complex behavior. A given degree of volume occupancy by larger macromolecules is predicted to have less effect on the structure and self-association of smaller macromolecules than the same degree of volume occupancy by smaller macromolecules has on the structure and self-association of larger macromolecules.

Excluded volume as a determinant of macromolecular structure and reactivity

The stability of the heme-globin linkage in some normal, mutant, and chemically modified hemoglobins.

Labeling of hemoglobin with pyridoxal phosphate.

The polymerization of mixtures of Hb S with hemoglobins A, A2, and F has been investigated by analysis of the proportions of S and non-S hemoglobin both in the supernate and in the pellet after centrifugation. In all cases the non-S hemoglobin was incorporated into the polymer even in the absence of hybrids in the order A > A2 > F. The solubility of Hb S is substantially increased by the other hemoglobins, especially by Hb F, which would account for its antisickling effect. It appears that the excluded volume effect of the other hemoglobin on Hb S is largely counterbalanced by the solubilizing effect arising from the interaction between the two hemoglobins in solution. The ability of hybrid hemoglobins to gel was demonstrated directly with tetramers in which alpha beta s dimers were covalently linked to alpha beta A, alpha delta A2, and alpha gamma F dimers.

Solubilization of hemoglobin S by other hemoglobins

The solubility of 14 hybrid haemoglobins composed of α chains with a single substitution and β chains from HbS was compared with that of sickle haemoglobin. A substantial reduction in the insolubility of native deoxyhaemoglobin S results from surface mutations in certain regions of the α chain while changes in other areas have no effect. Also, the chemical nature of the substitution is decisive and points to the type of intermolecular bonding at several loci.

Suzanna Kwong

Papers

The stability of the heme-globin linkage in some normal, mutant, and chemically modified hemoglobins.

Labeling of hemoglobin with pyridoxal phosphate.

Solubilization of hemoglobin S by other hemoglobins

Location and bond type of intermolecular contacts in the polymerisation of haemoglobin S

Oxygen affinity as an index of hemoglobin S polymerization: A new micromethod