Oxygen affinity responses to 2,3-diphosphoglycerate, and methaemoglobin formation in horse and human haemoglobins.

The oxygen affinities of horse and human haemoglobins were compared in the absence and presence of the allosteric effector 2,3-diphosphoglycerate (2,3-DPG). Horse haemoglobin solutions showed significantly smaller responses to the presence of 2,3-DPG, and this difference may be due to different amino acid substitutions at position NA2(2)beta. Horse haemoglobin solutions from erythrocytes containing different ratios of the two different haemoglobin types showed similar oxygen affinities in the absence and presence of 2,3-DPG. Horse haemoglobins in solution were found to autoxidise to methaemoglobin much more readily than human haemoglobin under the same conditions, and this is an important consideration when measuring the oxygen affinity of horse haemoglobin solutions. This difference could be due to different amino acid residues at position NA2(2)beta.