RT Journal Article
SR Electronic
T1 Hemoglobin Non-equilibrium Oxygen Dissociation Curve
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 2020.01.09.900001
DO 10.1101/2020.01.09.900001
A1 Rosella Scrima
A1 Sabino Fugetto
A1 Nazzareno Capitanio
A1 Domenico L. Gatti
YR 2020
UL http://biorxiv.org/content/early/2020/01/09/2020.01.09.900001.abstract
AB Abnormal hemoglobins can have major consequences for tissue delivery of oxygen. Correct diagnosis of hemoglobinopathies with altered oxygen affinity requires a determination of hemoglobin oxygen dissociation curve (ODC), which relates the hemoglobin oxygen saturation to the partial pressure of oxygen in the blood. Determination of the ODC of human hemoglobin is typically carried out under conditions in which hemoglobin is in equilibrium with O2 at each partial pressure. However, in the human body due to the fast transit of RBCs through tissues hemoglobin oxygen exchanges occur under non-equilibrium conditions. We describe the determination of non-equilibrium ODC, and show that under these conditions Hb cooperativity has two apparent components in the Adair, Perutz, and MWC models of Hb. The first component, which we call sequential cooperativity, accounts for ∼70% of Hb cooperativity, and emerges from the constraint of sequential binding that is shared by the three models. The second component, which we call conformational cooperativity, accounts for ∼30% of Hb cooperativity, and is due either to a conformational equilibrium between low affinity and high affinity tetramers (as in the MWC model), or to a conformational change from low to high affinity once two of the tetramer sites are occupied (Perutz model).