title: Changes in the Bohr effect due to pyridoxylation of the alpha-chain terminal amino groups of hemoglobin.
abstract: Deoxyhemoglobins substituted with pyridoxal 5'-phosphate or pyridoxal 5'-deoxymethylenephosphonate at the N-terminal amino groups of the alpha-chains were investigated by 31P-NMR spectroscopy. Titration curves of the 5'-side-chains show a substantial increase in acid strength in alpha-pyridoxylated deoxyhemoglobins when compared to the corresponding CO-liganded hemoglobins. These derivatives therefore contain a new oxygenation-linked acid group which opposes the normal Bohr effect. The loss in stabilization of the monoanion of the phosphate or phosphonate group derived from the three-dimensional structure can account for the lower pK of this ionization in deoxyhemoglobin as compared to CO-liganded hemoglobin. The reduction in the Bohr effect caused by modification of the alpha-chains with pyridoxal 5'-deoxymethyl-enephosphonate is quantitatively equal to the expected contribution of alpha-chain N-terminal amino groups.
mesh_terms: D000494:Allosteric Regulation; D000595:Amino Acid Sequence; D005914:Globins / Q000502:physiology*; D006441:Hemoglobin A / Q000502:physiology*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D011732:Pyridoxal Phosphate
chemical_list: D011732:Pyridoxal Phosphate; D005914:Globins; D006441:Hemoglobin A