The effect of temperature on the reaction of carbon monoxide with oxygenated haemoglobin.

1. The rate at which carbon monoxide displaces oxygen from its combination with haemoglobin in solution, has been measured spectrophotometrically, using a rapid-mixing stopped-flow technique. 2. In the presence of carbon dioxide, 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 non-linear, and a different curve is obtained at each carbon monoxide concentration. 4. From measurements of the rate constant at temperatures between 5 and 35 degrees C, it is concluded that the non-linearity is due to the formation at a finite rate of an intermediate complex, CO2Hb4O6, by the reaction of carbon dioxide with Hb4O6.