Age-dependence of molecular and functional changes in biological membrane properties.

Some general aspects including results on the possible mechanisms of membrane ageing are reviewed. The liquid-crystalline fluid state of a biological membrane is an essential condition for maintenance of different membrane functions. The liquid-crystalline state of different plasma membranes changes with age of the organism. The degree of unsaturated fatty acids decreases and the content of cholesterol increases during ageing. It could be shown that superoxide radicals originate from minor side-reactions of oxidoreductase enzymes. Ageing increases the amount of superoxide radicals. A small amount of radicals escape quenching by superoxide dismutase. The formation of radicals leads to degradation of membrane lipids. The age-dependent changes in membrane lipid composition influence respiratory activity in rat heart mitochondria of old animals. Rat liver plasma membrane lipids also show a decrease in membrane fluidity which results in a change in transport parameters of cholic acid and thymidine. The change in age-dependent lipid-protein interactions was demonstrated by spin-label measurements in model membranes. The results demonstrated that peroxidative break-down of lipids is an ongoing post-transcriptional process of ageing. The possible role of protective repair mechanisms is discussed.