Subunit Dissociation of the Abnormal Hemoglobins G Georgia (α295Leu(G2) β2) and Rampa (α295Ser(G2) β2)

The liganded derivatives of hemoglobins G Georgia (α295Leu(G2) β2) and Rampa (α295Ser(G2) β2) were found by sedimentation velocity, viscosity, and diffusion measurements to be extensively dissociated into dimers in 0.1 mNaCl at pH 7.2 to 7.4 and 25°. The deoxygenated derivatives of both hemoglobin variants are tetramers under the same conditions. The deoxyhemoglobins also retain a predominantly tetrameric structure in NaCl solutions of increasing concentration up to 2 m, and in dilute alkaline buffers, at least to pH 9.8. In addition, association-dissociation in oxy- or cyanferrihemoglobin Rampa is both pH- and temperature-dependent. The liganded Rampa molecule is primarily a tetramer at 4° in the pH range 6 to 7, whereas liganded hemoglobin G Georgia shows only slightly increased tetramer formation under identical conditions. Both hemoglobin G Georgia and hemoglobin Rampa have decreased heme-heme interactions and increased oxygen affinities.