Saturation transfer electron paramagnetic resonance detection of sickle hemoglobin aggregation during deoxygenation

Spin-label saturation transfer EPR (ST-EPR) methods have been used to study the sickle hemoglobin (HbS) aggregation behaviors induced by slow deoxygenation at a constant temperature of 30 degrees C, and by a rapid temperature increase from 1 degree to 30 degrees C for fully deoxygenated HbS. For slow deoxygenation at 30 degrees C, we find that the effective HbS correlation time exhibits a continuous increase, without any abrupt transitions, suggesting that polymer formation in concentrated HbS at high temperature occurs even at high oxygenation levels. Upon a rapid temperature increase, fully deoxygenated HbS exhibits a short delay time, then an abrupt increase in effective correlation time. These results also indicate that ST-EPR provides a useful method for probing the molecular dynamics of HbS aggregation.