Abstract
1. Spectrophotometric measurements, using a rapid mixing and stopped flow technique, have been made of the rate at which CO displaces O2 from its combination with haemoglobin.
2. In haemoglobin solutions, buffered at pH 7·2 and 9·1, the reaction proceeds by a unimolecular dissociation as proposed by Gibson & Roughton (1955). In a Ringer—Locke solution, equilibrated with a PCO2 of 3 cmHg and at pH 7·4, the reaction of HbO2 with CO is a two-stage process, with a transition from one form of Hb4O6 to another.
3. An investigation of the reaction between CO and HbO2 in erythrocytes, suspended in Ringer—Locke solution, indicates that the rate is determined by the chemical reaction and this also is a two-stage process.
4. The transition is probably associated with the reaction of CO2 with Hb4O6, following the dissociation from fully saturated oxyhaemoglobin of an oxygen molecule. It alters the relative velocity constants of the reactions of O2 and CO with Hb4O6 by 100:1.
5. The implications of these proposals of the equilibria of haemoglobin with CO and O2 are discussed. The difference between the sigmoid equilibria curves at high HbO2 and HbCO values can be explained as due to the different reaction pathways.
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Selected References
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