The egress of oxygen from sheep erythrocytes after mixing with sodium dithionite

Spectrophotometric measurements, using the rapid-mixing technique, have been made of the initial rate of egress of oxygen from HbO₂ in sheep erythrocytes after mixing with dithionite. This rate is $\text{18}\text{sec}{}^{\mathrm{-1}}\text{± 20\%}$ at 25° and the activation energy is $\text{14}\text{kcal}\text{± 20\%}$ for HbB. No variation was found with a change of oxygen concentration from 0.075–0.35 mM at 10°, nor with a change of Na₂S₂O₄ concentration from 4–12 g/l. The rate of dissociation was found to be greater, during the later part of the reaction, with the stopped-flow system as compared with the constant-flow technique. An analysis of the results suggests that the cell membrane has negligible resistance to the egress of oxygen and that the initial rate is determined by the chemical reaction of $\text{HbO}{}_2\text{→}\text{Hb}$. It is also suggested that the internal contents of the erythrocyte may be effectively mixed.