The Hemoglobin Conformation in Erythrocytes at Different Levels of Oxygen Partial Pressure

Abstract

The variation in the conformations of hemoglobin heme and globin in response to different oxygen partial pressures (pO₂) has been studied by Raman spectroscopy inside erythrocytes and in hemoglobin dissolved in incubation medium. The spectra of hemoglobin inside erythrocytes and in the medium show that several characteristic bands in the range from 1000 to 1700 cm^–1 (stretching vibrations in the heme group) and in the high-frequency range from 2800 to 3000 cm^–1 (stretching vibrations in globin amino acids) vary with pO₂ levels. The curve of hemoglobin saturation with oxygen (sO₂) obtained from the Raman-scattering data displays sigmoidal behavior only in hemoglobin inside erythrocytes. It has been shown that differences in heme conformation at different pO₂ levels affect the ability of hemoglobin to form complexes with nitric oxide. As the pO₂ level increases, the conformational changes of hemoglobin heme in the cell entail an increase in the contribution of vibrations of lateral –CH₃ groups in pyrrole half-rings and group vibrations of bonds inside pyrrole half-rings, whereas the globin conformation is associated with a higher contribution of vibrations from H-methine groups and symmetrical terminal methylene groups in amino acids.