Age differences in the positional distribution of phosphoglycerides and molecular species of choline phosphoglycerides during development of the chick embryo liver

Abstract

The total fatty acid composition and the distribution of acyl groups in the positions 1 and 2 of 1,2-diacyl- sn-glycero-3-phosphocholine and 1,2-diacyl- sn-glycero-3-phosphoethanolamine as well as in the molecular species of 1,2-diacyl- sn-glycero-3-phosphocholine from the chick embryo liver have been investigated at various stages of development. The fatty acid content of the main lipid classes from the yolks was also evaluated. The relative percentages of total saturated fatty acids in 1,2-diacyl- sn-glycero-3-phosphocholine remained constant during liver development; however, the levels of both main saturated acids, palmitic and stearic acids, were reciprocally counterbalanced as the age of the embryo proceeded. On the other hand, arachidonic acid decreased with time whereas linoleic acid and docosahexaenoic acid doubled their proportions during development. The relative amounts of total saturated fatty acids from liver 1,2-diacyl- sn-glycero-3-phosphoethanolamine were also constant during all stages of development; however, palmitic/ stearic acid ratio did not change with time in this phosphoglyceride. Fatty acid composition of the yolk phosphoglycerides did not change during embryonic development. It should be noted that marked differences between fatty acid composition of choline and ethanolamine phosphoglycerides from the embryo liver and those of the yolk phosphoglycerides were demonstrated. The general patterns of the positional distribution of the acyl groups in choline phosphoglycerides differed from those of ethanolamine phosphoglycerides. Palmitic and stearic acids were only positioned at position 1 in 1,2-diacyl- sn-glycero-3-phosphoethanolamine whereas both fatty acids did not acylate exclusively the position 1 in 1,2-diacyl- sn-glycero-3-phosphocholine. Some unsaturated fatty acids were located in both positions of both phosphoglycerides, poly-unsaturated acids being positioned exclusively at position 2. Age related changes in the acyl groups were mainly revealed in choline phosphoglycerides, stearic and linoleic acids replacing respectively palmitic acid (position 1) and arachidonic acid (position 2). Choline phosphoglycerides were fractionated in fifteen main molecular species in which the positional distribution of fatty acids was determined. 1,2-Dipalmitoyl- sn-glycero-3-phosphocholine was the main component of disaturated molecular species, the level of which (about 10%) remained unchanged until the 17th day of development and decreased afterwards until hatching. The molecular species containing saturated and unsaturated fatty acids were dominant in all stages of development of the embryo liver. The saturated fatty acids were predominantly palmitic and stearic acids acylating at position 1; the unsaturated fatty acids acylating at position 2 included oleic acid, linoleic acid, arachidonic acid and docosahexaenoic acid. Among these molecular species, those containing linoleic and arachidonic acids accounted for 70–80% of the total choline phosphoglycerides. The relative amounts of 1-palmitoyl-2-arachidonoyl- sn-glycerophosphocholine decreased while 1-stearoyl-2-linoleoyl- sn-glycero-3-phosphocholine increased during embryo development. Molecular species containing either two identical or different unsaturated fatty acids were quantitatively unimportant.