Danek Elbaum

Surface activity of hemoglobin S and other human hemoglobin variants

The kinetics of surface pressure change (deltapi vs. t isotherms) were determined for several single point mutations of the human hemoglobin system. It was observed that hemoglobin S and hemoglobin CHarlem (both containing beta6 Glu leads to Val substitutions) have a specific behavior at the water-air interface: their extent of surface pressure change is larger than for hemoglobin A, hemoglobin C and hemoglobin Korle Bu (beta73 Asp leads to Asn). In addition, hemoglobin S seems to occupy a larger area per molecule than hemoglobin A. The conformational requirements for this property, in addition to the beta6 Val substitution, appear to be the liganded state of the betas chain in the tetramer. Electrostatic, hydrogen bonding and hydrophobic interactions are involved in determining the surface activity of a hemoglobin molecule. The differences between the surface activity of oxyhemoglobin S and oxyhemoglobin A could be the basis for their differences in mechanical precipitability, although other factors may play a role.

Kinetics of Hb S gelation Effect of alkylureas, ionic strength and other hemoglobins

Using a light scattering (turbidity) method to estimate the delay time of gelation of deoxy hemoglobin S hemolysates, we have examined the effects of various alkylureas, variations in ionic strength by addition of NaCl, and admixture with other hemoglobins on gelation kinetics. Each of these factors substantially prolonged the delay times to different extents, but the dependence of the delay times on a high power of the hemoglobin concentration varied only slightly. These findings suggest that the events preceding gelation, most likely the formation of nuclei, are affected by these factors, but the critical nuclear size for gelling is fairly constant. Parallel changes indicated good qualitative correlation between gelation, delay times, minimum gelling concentrations of solutions of mixed hemoglobins and kinetics of sickling of red cells containing these mixtures, with the exception of hemoglobin Charlem trait cells the sickling kinetics of which were slower than predicted by the solution properties.

Oxyhemoglobin A and oxyhemoglobin S films at an air-water interface: Absorption spectra studies

Abstract Properties of oxyhemoglobin at an interface are important to further the understanding of tertiary and quaternary changes in hemoglobin. Absorption spectra of oxyhemoglobin films were studied directly at the air-water interface. Both oxy Hb A and oxy Hb S show a bathochromic shift in the Soret band as compared to the solution spectra. No spectral difference is observed between oxy Hb A and oxy Hb S. However, surface isotherms show a greater unfolding of the molecule for oxy Hb S than oxy Hb A. Hemolysates appear to be more stable on the surface than their corresponding chromatographed material. The lack of spectral shift upon compression might be the consequence of the high dielectric constant of the medium. A model for this surface phenomenon with respect to observed mechanical precipitation of oxy Hb S is discussed.

Decreased Binding of 2,3-Diphosphoglycerate to Deoxy Hemoglobin S: A Polymerization-Independent Functional Abnormality

ABSTRACT Binding of the 2,3-diphosphoglycerate to Hb A and Hb S was studied using proton uptake measurements. As expected from oxygen affinity and CO2, competition experiments,18 the binding constant of deoxy Hb S for 2,3-diphosphoglycerate was lower than that for deoxy Hb A. This result represents a functional abnormality of the deoxy Hb S molecule that is independent of a polymerization properties and suggests a small alteration of the conformation of the N termini of the βs chain.