Observations on the Kinetics of the Reaction of Hemoglobin with Oxygen

The kinetics of the reaction of human deoxyhemoglobin with oxygen at high concentrations of ligand (∼10-4 m) has been studied with the use of a fast stopped flow apparatus with a dead time of approximately 300 µsec. The shape of the progress curve reveals that the apparent second order rate constant for the reaction with oxygen (k') increases with the extent of the reaction, similar to what was reported for other ligands (i.e. carbon monoxide). Within the oxygen concentration range studied, the rate of the reaction at any stage is proportional to the ligand concentration, notwithstanding the change in rate as the reaction proceeds. These results are interpreted to indicate that the ligand-linked intramolecular change in hemoglobin is a fast process which occurs in a fraction of a millisecond.