Evidence for carbon monoxide binding to sickle cell polymers during melting

The melting of sickle cell hemoglobin (HbS) polymers was induced by rapid dilution using a stopped-flow apparatus. The kinetics of polymer melting were monitored using light scattering. Polymer melting in the absence of any hemoglobin ligand was compared to melting when the diluting buffer was saturated with carbon monoxide (CO). In this way the role of CO in polymer melting could be assessed. The data were analyzed using models that assumed that melting occurs only at the ends of polymers. It was further assumed that CO could only bind to HbS in the solution phase. However, our data could not be fitted to this model, where CO cannot bind directly to the polymer. Thus, CO probably binds directly to the polymers during our melting experiments. This result is discussed in terms of oxygen induced polymer melting and polymerization processes in sickle cell disease