title: Quaternary equilibrium analysis of the imidazole methemoglobin bound with inositol hexaphosphate.
abstract: The visible and proton NMR spectral responses of imidazole methemoglobin by the binding of inositol hexaphosphate were examined in the 2-40 degrees C range. The magnitude of the +/- (inositol hexaphosphate) visible difference spectrum increased and the intensity of the 33 ppm NMR peak decreased with lowering of the temperature. The NMR results were quantitatively analyzed with a simple two-state allosteric model. The results show that the T conformer fraction is 0.6 at 20 degrees C and that the equilibrium shifts toward the T state at lower temperature. The large changes in delta H and delta S associated with the equilibrium suggest participation of numerous factors in the determination of the equilibrium position. The increase in the T conformer population of imidazole methemoglobin, which is pure low-spin, suggests that the appearance of the T state with decreasing temperature is not directly coupled to an increase in spin of the heme iron.
mesh_terms: D000328:Adult; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008433:Mathematics; D008706:Methemoglobin / Q000378:metabolism*; D010833:Phytic Acid / Q000378:metabolism*; D013696:Temperature
chemical_list: D010833:Phytic Acid; D008706:Methemoglobin