Two-state analysis for allosteric properties of abnormal hemoglobins

To shed light upon the understanding of structure and function relationship of hemoglobin, we determined the oxygen equilibrium curves of a series of alpha 1 beta 2 contact anomalous hemoglobins, low and high spin derivatives of valency hybrid hemoglobins and normal hemoglobin under various conditions comparable with each other using an automatic recording apparatus. The Hill plots of their curves were analyzed by a trial and error method without any assumptions using computer graphic display. The results deduced from these analyses are as follows. Anomaly in alpha 1 beta 2 contact region, weakening or rupture of the Bohr effect and Cl- dependent salt-bridges, small displacement of heme iron from porphyrin plane result in not only shifting the R--T equilibrium towards R but also raising the oxygen affinity of the T state to various extents. IHP binding can oppose these effects. A relation that the change in L strongly depends upon the change in c was newly discovered. These results suggest that the T state of individual Hb takes a single structure of many heterogeneous T quaternary structures depending on its function.