Phospholipids in tissues of the eye. 3. Composition and metabolism of phospholipids in human lens in relation to age and cataract formation.

Abstract

Abstract 1. 1. In human lens a marked change in phospholipid composition occurs during life. This is mainly caused by a continuous net synthesis of sphingomyelin and by a decrease in concentrations of the other phospholipids at higher age. 2. 2. These changes are correlated with the process of cell differentiation and the formation of the lens nucleus, as appeared from investigations of cortex and nucleus. Some similarities with developing brain were observed. 3. 3. 32 P i is rapidly incorporated into phosphatidic acid and phosphatidylinositol, while the ethanolamine and choline glycerophospholipids show a much lower phosphate turnover. These components contain, besides diacyl phospholipids, also vinylether analogues which have a low metabolic activity. 4. 4. The phospholipid composition of senile cataracts is similar to those of normal lenses of the same age. The amounts of bound lipids and of proteolipids decrease, which is an indication of membrane disintegration. The phosphate incorporation into phosphatidylinositol decreases while that into phosphatidic acid and phosphatidylglycerol increases.