The Dissociation of the First Oxygen Molecule from Some Mammalian Oxyhemoglobins

The velocity of dissociation of oxygen from the α and β chains of saturated tetrameric oxyhemoglobin has been measured by detailed analysis of the time course of the replacement of oxygen by carbon monoxide. The rates for α chains vary over a 6-fold range, the lowest rate, for guinea pig hemoglobin, being only 2.5 sec-1 at pH 9 and 20°. When compared with isolated chains, the rates for human α chains within the hemoglobin molecule are decreased 2-fold; the rates for β chains are little affected. The rates for the β chains from man, horse (two electrophoretic types), guinea pig, and sheep (two electrophoretic types) are all larger than the corresponding α chain rates, vary over a 3-fold range, and are slightly slower at pH 9 than at pH 7.