Functional and structural analyses on abnormal hemoglobins with impaired oxygen binding properties—To elucidate the allosteric mechanism of hemoglobin

Abstract

The altered oxygen binding curves for various abnormal hemoglobins were analyzed according to a two-state allosteric model. Of three allosteric parameters computed for abnormal hemoglobins, KR was nearly constant, but KT and L varied with the correlation of log c=−0.4 log L, where c is KR/KT. This correlation indicates that the abnormal allosteric oxygen binding of hemoglobin is due to altered molecular properties of the deoxy-T state but not that of the deoxy-R state. To clarify the molecular basis of this idea, resonance Raman spectra in the low-frequency region of abnormal hemoglobins were measured under different solvent conditions. Varied frequencies of iron-histidine stretching Raman lines was found to correlate with varied oxygen affinities (KT) of deoxy-T states. The strength of the iron-histidine bond of deoxy-T states was changed, depending upon the magnitude of the strain imposed on hemes by globin, and this bond presumably comprises an important part of the regulation mechanisms for hemoglobin oxygen binding and structure changes.