MORPHOLOGICAL AND BIOCHEMICAL ANALYSES OF LIPID GRANULES ISOLATED FROM FAT-STORING CELLS IN RAT LIVER

Lipid granules in fat-storing cells4 were isolated from the rat liver. Electron microscopic studies revealed that the lipid granule fraction contained electron-dense, spherical lipid granules 0.3 to 3 μm in diameter. Vitamin A was demonstrated in the isolated lipid granules by fluorescence microscopy and fluorescence microscope spectrophotometry. The isolated lipid granules consisted of 83% lipids and 14% proteins. The lipid composition was 50% triacylglycerol, 12% vitamin A (mainly retinyl palmitate), 10% cholesteryl ester, 6% free fatty acid and 5% phospholipids. Only a trace amount of retinol or cholesterol was detected. Two major peptides with molecular weights of 33,000 and 28,000 were demonstrated by SDS-polyacrylamide gel electrophoresis. The activities of retinyl palmitate hydrolase and tripalmitin hydrolase in the isolated lipid granules were 3 to 5 times higher than those in the liver homogenate. The lipid granules contained less than 5 ppm of zinc and copper. The chemical composition and ultrastructure of lipid granules in fat-storing cells were similar to those of the plasma lipoproteins, but not to those of the fat globules in white adipose cells.