The fatty acids of phosphatidylethanolamine and phosphatidylcholine from hen's egg.

Glycerides and phospholipids from the same tissue exhibit appreciable differences in their fatty acid composition (Hilditch, 1956; Futter & Shorland, 1957), but very little is known about the distribution of fatty acids among the individual phospholipids. Progress in working out the pathways of phospholipid synthesis in living cells (Kennedy & Weiss, 1956; Smith, Weiss & Kennedy, 1957) has, however, stimulated interest in individual phospholipid compounds as chemical entities, rather than as mixtures. Consequently, it has become of interest to know if any selectivity with regard to fatty acids has occurred in the biological synthesis of phospholipids such as phosphatidylcholine and phosphatidylethanolamine. Because the individual lipids have not been separated in anything like quantitative yield this question has remained unanswered, although, working qualitatively, Klenk & Bohm (1951) found marked differences in the fatty acid composition of phosphatidylserine and phosphatidylethanolamine from ox brain. Recently, however, Rhodes & Lea (1957) have isolated almost quantitatively the component phospholipids in egg yolk on silicic acid and alumina columns. These authors isolated, in essentially pure form, all the phosphatidylethanolamine and 97 0% of the phosphatidylcholine. Two other fractions contained mixtures of the minor constituents-lysophosphatidylcholine and sphingomyelin in one fraction and lysophosphatidylethanolamine and inositol phospholipid in the other. More progress has been made in the elucidation of the composition of the phospholipid fraction in egg yolk than of the phospholipids in any other biological material. Contributing factors have been the ready availability of this phospholipid and the less divergent nature of its principal components. Rhodes & Lea (1957) found egg phospholipid to contain phosphatidylcholine 73 0, lysophosphatidylcholine 5-8, sphingomyelin 2-5, phosphatidylethanolamine 15-0, lysophosphatidylethanolamine 2-1, and inositol phospholipid 0-6, expressed as moles %. In the present work the egg phospholipids have been separated into two fractions, one containing phosphatidylethanolamine and the other containing the remaining components, among which phosphatidylcholine predominates. The fatty acids in each fraction have been examined.