Molecular Species of Glycerophosphatides and Triglycerides of Egg Yolk Lipoproteins

Abstract

Four major density classes of lipoproteins were isolated from hen's egg yolk by conventional ultracentrifugation and each class was subjected to thin-layer chromatography on hydroxylapatite. Lipid extracts were obtained from the total egg yolk, the density classes recovered at each stage of centrifugation and from the fractions resolved on hydroxylapatite. The proportions of the lipid classes in the total lipid extracts were determined by direct gas chromatography. The molecular species of the glycerides and phospholipids were identified by means of specific enzymic hydrolyses following isolation of the lipid classes by thin-layer chromatography.The results indicate that the major differences in the lipid composition of the egg yolk lipoproteins are confined to variations in the proportions of cholesterol, triglycerides, and phospholipids. There are lesser differences in the proportions of the various phospholipid classes among the different lipoproteins. All lipoprotein classes, except the water-soluble fraction, contained the same species of each phospholipid and triglyceride. The lipids of the water-soluble fraction were more saturated than those of the other lipoproteins.