METABOLISM OF THE YOLK PHOSPHOLIPIDS BY THE DEVELOPING CHICK EMBRYO

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Abstract
A study was made of the concentrations and fatty acid compositions of the various phospholipids in the yolks of fertile unincubated eggs and in the yolks of eggs that had been incubated for 13,15,17,19, and 21 days. Phosphatidyl choline and phosphatidyl ethanolamine accounted for 69 and 24% respectively of the total phospholipids present in the yolk of the unincubated egg. The remaining 7% was accounted for by small amounts of phosphatidyl serine, sphingomyelin, and a phospholipid fraction that was tentatively identified as diphosphatidyl glycerol. Although the percentage of total phospholipids in the total yolk lipid did not vary during incubation, there was a pronounced increase in the phosphatidyl choline: phosphatidyl ethanolamine ratio as incubation proceeded. The phosphatidyl ethanolamine fraction was the only phospholipid fraction present in the yolk that showed any consistent change in fatty acid composition during incubation. The concentration of docosahexaenoic acid in the fatty acids of the yolk phosphatidyl ethanolamine decreased from 8% on day 0 to 1.6% on day 21. It is suggested that the developing embryo preferentially absorbs from the yolk a phosphatidyl ethanolamine fraction that is relatively rich in docosahexaenoic acid.