Circular dichroism spectra of human hemoglobin reveal a reversible structural transition at body temperature
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Previously we have shown that human red blood cells (RBCs) undergo a sudden change from blocking to passing through a 1.3±0.2-µm micropipette when applying an aspiration pressure of 2.3 kPa at a critical transition temperature (Tc=36.4±0.3 °C). Low-shear viscosity measurements suggested that changes in the molecular properties of hemoglobin might be responsible for this effect. To evaluate structural changes in hemoglobin at the critical temperature, we have used circular dichroism (CD) spectroscopy. The thermal denaturation curves of human hemoglobin A (HbA) and hemoglobin S (HbS) upon heating between 25 and 60 °C were non-linear and showed accelerated denaturation between 35 and 39 °C with a midpoint at 37.2±0.6 °C. The transition was reversible below 39 °C and independent of solution pH (pH 6.8–7.8). It was also independent of the oxygenation state of hemoglobin, since a sample that was extensively deoxygenated with N2 showed a similar transition by CD. These findings suggest that a structural change in hemoglobin may enable the cellular passage phenomenon as well as the temperature-dependent decrease in viscosity of RBC solutions.
KeywordsCircular dichroism Heat denaturation Hemoglobin oxygenation state Red blood cells
- Kinderlerer J, Lehmann H, Tipton KF (1970) Thermal denaturation of human haemoglobins. Biochem J 119:66P–67PGoogle Scholar
- Makarevic J, Jokic M, Frkanec L, Katalenic D, Zinic M (2002) Gels with exceptional thermal stability formed by bis(amino acid) oxalamide gelators and solvents of low polarity. Chem Commun (Cambridge) 2238–2239Google Scholar
- Walters MC, Nienhuis AW, Vichinsky E (2002) Novel therapeutic approaches in sickle cell disease. Hematology (Am Soc Hematol Educ Program) 10–34Google Scholar