An analysis of the stopped-flow kinetics of gaseous ligand uptake and release by adult mouse erythrocytes.
Ligand uptake and release by the haemoglobin contained within adult mouse erythrocytes was studied by using dual-wavelength stopped-flow techniques. The rate of O2 uptake is very much lower than that expected for an equivalent concentration of haemoglobin in free solution. The O2-concentration-dependence found in uptake experiments is greater than first-order. CO uptake shows the same pattern of reactivity as does O2, but the associated rates of uptake are lower and the concentration-dependence of the CO rates is first-order. O2 release from the adult erythrocytes was measured by stopped-flow mixing with Na2S2O4. Under these circumstances the deoxygenation of intracellular haemoglobin shows accelerating time courses. The apparent rate-constant-dependence on dithionite concentration shows a rate limit at high reductant concentrations. Computer simulations of both ligand uptake and release processes were carried out by using a three-dimensional model. The simulations clearly indicate that in rapid-mixing experiments the rather slow experimentally observed O2 uptake rate is due to rate-limiting diffusion through an extracellular stagnant solvent layer. In the case of O2 release, however, the major rate-controlling process is the rate of O2 dissociation from the haemoglobin molecules, which accelerates during the deoxygenation process.
Brittain
T
T
Department of Biochemistry, University of Auckland, New Zealand.
Simpson
R
R
D000818:Animals; D002245:Carbon Dioxide / Q000097:blood; D004912:Erythrocytes / Q000378:metabolism*; D006454:Hemoglobins / Q000378:metabolism; D007700:Kinetics; D008024:Ligands; D051379:Mice; D008810:Mice, Inbred C57BL; D010100:Oxygen / Q000097:blood*
D006454:Hemoglobins; D008024:Ligands; D002245:Carbon Dioxide; D010100:Oxygen