Regulation of the composition and positioning of saturated and monoenoic fatty acids in phosphatidylcholine.

The mechanism by which polyenoic acids control the amount and positioning of monounsaturated fatty acids in choline phosphoglycerides from baby hamster kidney cells was studied. Under normal growth conditions monoenoic acids were derived from the desaturation of saturated fatty acids and comprised over 50% of the fatty acids at position 1 of the glycerol moiety. The monoene content of positions 1 and 2 decreased in response to the addition of di- and polyenoic acids to the culture medium. All the di- and polyenoic acid supplements tested inhibited the desaturation of palmitic and stearic acid and replaced monoenes at position 2. However only linoleic, linolenic, and eicosadienoic acids replaced monoenes at position 1. The results suggest that under appropriate conditions up to 25% of the choline phosphoglyceride fraction consisted of a stable molecular species containing di- or trienoic fatty acids at both the 1 and 2 positions of glycerol moiety. With eicosatrienoic or arachidonic acid supplements, on the other hand, the monoenes at position 1 were replaced with saturated fatty acids. The magnitude of these effects, particularly at position 1, was proportional to the concentration of the fatty acid supplement. The results suggest that polyenes with at least 20 carbon atoms can play a key role in determining the ultimate composition and positioning of fatty acids in baby hamster kidney choline phosphoglycerides and that this control is mediated by their ability to inhibit delta 9 desaturase and by a retailoring system specific for these polyenes.