Ligand uptake and release by the haemoglobin contained within adult mouse erythrocytes was studied by using dual-wavelength stopped-flow techniques. The rate of 02 uptake is very much lower than that expected for an equivalent concentration of haemoglobin in free solution. The 02-concentration-dependence found in uptake experiments is greater than first-order. CO uptake shows the same pattern of reactivity as does 029 but the associated rates of uptake are lower and the concentration-dependence of the CO rates is firstorder. 02 release from the adult erythrocytes was measured by stopped-flow mixing with Na2S204. 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 02 uptake rate is due to rate-limiting diffusion through an extracellular stagnant solvent layer. In the case of 02 release, however, the major rate-controlling process is the rate of 02 dissociation from the haemoglobin molecules, which accelerates during the deoxygenation process.
Hypercalcaemia occurring after ten weeks of immobilisation was observed in four adult patients all of whom had had prior renal failure sufficient to require renal dialysis. In all patients parathyroid hormone levels were normal or low and in three plasma 1,25(OH)2D3 levels were low. These findings are consistent with immobilisation induced increases in bone calcium resorption. Renal excretion of calcium may have been impaired by renal dysfunction resulting in hypercalcaemia and suppression of plasma PTH and 1,25(OH)2D3 levels. Resolution of the hypercalcaemia was associated with remobilisation. Parathyroidectomy is inappropriate treatment.
The processes of O2 uptake and release by the three embryonic haemoglobins contained within early mouse embryonic red blood cells have been studied using dual-wavelength stopped-flow kinetic spectroscopy. The rate of O2 uptake in the pseudo-spherical, nucleated, embryonic red blood cells exhibits a greater than first-order dependence on O2 concentration. The time courses for the release from the red blood cells into dithionite-containing solutions tends towards a limiting rate at high dithionite concentrations. The rates of both the uptake and release processes observed in the embryonic cells are compared with those previously seen for adult mouse red blood cells. A new mathematical model is described which accurately simulates both uptake and release experimental data for the nucleated embryonic red blood cells.
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