Sickle-cell hemoglobin: fall in osmotic pressure upon deoxygenation.

Macromolecules such as hemoglobin exert both kinetic and matrix effects on osmotic pressure. The kinetic osmotic pressure of sickle-cell hemoglobin is lost upon deoxygenation at physiological erythrocyte concentrations. The non-kinetic or matrix component of osmotic pressure remains relatively unchanged. Loss of thermal-osmotic activity during deoxygenation occurs throughout a hemoglobin concentration range between 2.5 and 35 g/100 ml. Deoxygenation of sickle-cell hemoglobin causes aggregation such that the matrix effect is unchanged but the kinetic (van't Hoff) effect nearly vanishes. A loss of intracellular osmotic pressure during deoxygenation could dehydrate the erythrocyte sufficiently to promote more rapid sickle-cell hemoglobin aggregation. Subsequently, complete gelation of these aggregates could cause additional water loss and thrust the sickled cell into an irreversible cycle. The osmotic pressure of normal hemoglobin does not change appreciably during deoxygenation and is essentially the same as the osmotic pressure of oxygenated sickle-cell hemoglobin.