| Abstract: | Erythrocyte plasma membranes were isolated from a homogeneous population of human or rabbit erythrocytes fractionated into classes representing young, middle-age and old age in vivo. Lipid analyses of human erythrocyte plasma membranes reveal a decrease of the cholesterol to phospholipid molar ratio, followed by a marked decrease in the activities of the membrane-bound enzymes (Na+,K+)-stimulated ATPase, acetylcholinesterase and NAD+ase from young to old age. Such changes were not observed between young and middle-age rabbit erythrocytes. Incubation of rabbit young erythrocytes with phosphatidylcholine vesicles (liposomes) to obtain partial depletion of their membrane cholesterol, indicated that cholesterol depletion causes a statistically significant decrease of the (Na+,K+)-stimulated ATPase and acetylcholinesterase activities, but the NAD+ase activity remained almost unchanged. The biological significance of these data are discussed in terms of the differences and modifications in the interaction of membrane-bound enzymes with membrane lipids during in vivo ageing of erythrocytes. |
