The egress of oxygen from human HbO₂ in solution and in the erythrocyte

Spectrophotometric measurements, using the rapid-mixing constantflow and stopped-flow techniques, have been made of the rate of egress of oxygen from human HbO(2) in solution and in erythrocytes.2. By 1:20 dilution in a medium containing a high concentration of carbon monoxide k(4), the rate constant of the reaction Hb(4)O(8) --> Hb(4)O(6)+O(2) has been determined. At pH 7.4 and 20 degrees C, k(4) in solution was 42.0 sec(-1) and within the intact cell 41.4 sec(-1). The respective activation energies were 19.3 and 18 kcal.3. The rate of dissociation of HbO(2) to Hb, after mixing an erythrocyte suspension with Na(2)S(2)O(4), was identical, over at least 50% of the reaction, with the change of HbO(2) to HbCO above.4. An analysis of the data indicates that the cell membrane has little or no resistance to the passage of oxygen and the internal contents are effectively mixed.