The entropically favored osmotic "compression" of sickle cell hemoglobin gels.
Contrary to the accurate, hard-sphere depiction of monomeric hemoglobin in solution, sickle cell hemoglobin (HbS) polymerization/gelation requires attention to molecular interactions. From the temperature dependence of the osmotic compressibility of HbS gels, we were able to extract the entropy increase for concentrating HbS in this phase. Normalized per mole of water removed, the entropy increase from gel compression DeltaS(gel) is four times the previously measured DeltaS(trans), for the transition from monomeric HbS solution to HbS gel. The positive entropy change cannot emerge from the assembly of hard spheres but can indicate remodeling of HbS fibers driven by release of ordered water. The fourfold difference in DeltaS(gel) and DeltaS(trans) suggests that the act of initial fiber/gel formation from monomeric solution differs from the process of further polymerization due to tighter packing within the gel phase.
Chik
J K
JK
National Institute of Child Health and Human Development, Laboratory of Physical and Structural Biology, National Institutes of Health, Building 12A, Room 2041, Bethesda, MD 20892-5626, USA.
Parsegian
V A
VA
D019277:Entropy; D005782:Gels; D006451:Hemoglobin, Sickle / Q000737:chemistry*; D006801:Humans; D009994:Osmolar Concentration; D009997:Osmotic Pressure; D013816:Thermodynamics
D005782:Gels; D006451:Hemoglobin, Sickle