Aggregation effects on oxygen binding of sickle cell hemoglobin.

Area of Science:

• Biochemistry
• Hematology
• Molecular Biology

Background:

• Sickle cell disease is characterized by abnormal hemoglobin.
• Hemoglobin deoxygenation leads to polymerization and red blood cell sickling.
• Understanding hemoglobin's oxygen binding properties is crucial for disease mechanisms.

Purpose of the Study:

• To investigate the oxygen binding characteristics of deoxygenated sickle cell hemoglobin solutions.
• To correlate oxygen binding with physical changes like light scattering.
• To elucidate the impact of aggregation on hemoglobin's oxygen affinity.

Main Methods:

• Preparation of concentrated sickle cell hemoglobin solutions (0.33 g/mL).
• Measurement of oxygen binding curves during deoxygenation and oxygenation.
• Monitoring of light scattering properties of the solutions.

Main Results:

• A distinct "crisis point" was observed during deoxygenation, characterized by a steep oxygen binding curve (Hill coefficient of 5-6).
• A simultaneous increase in light scattering indicated molecular aggregation.
• Oxygen binding curves were nearly identical during oxygenation and deoxygenation, suggesting reversibility under these conditions.
• Hemoglobin aggregation was found to shift the oxygen binding curve towards higher pressures, indicating reduced oxygen affinity.

Conclusions:

• Concentrated sickle cell hemoglobin exhibits unique oxygen binding behavior upon deoxygenation, linked to aggregation.
• The observed steepness in the oxygen binding curve at the "crisis point" may signify a critical transition in hemoglobin's quaternary structure.
• Aggregation significantly influences sickle cell hemoglobin's oxygen affinity, potentially exacerbating cellular hypoxia in sickle cell disease.