The Bohr effect on the reaction of carbon monoxide with fully oxygenated haemoglobin

1. The rate at which CO displaces O2 from its combination with haemoglobin in solution, has been measured spectrophotometrically, using a rapid-mixing stopped-flow technique. 2. In the presence of CO2, the reaction proceeds by a unimolecular dissociation, with a rate constant r. 3. The relationship of the reciprocal of r to the ratio PO2/PCO is nonlinear, and a different curve is obtained at each CO concentration. 4. Measurements were made of the rate of the reaction when the pH was varied, with constant or varying PCO2. In both situations the value of r was found to have a miximum, for a given PO2/PCO ratio and CO cencentration, at pH 7.2. 5. An analysis of these results suggest that the Bohr effect, of pH and PCO2, is a dynamic equilibrium between four stable tertiary states of each of the alpha and beta chains. Each intermediatory complex has different rate constants for CO and O2.