Positional distribution of fatty acids in fish and other animal lecithins

Phosphatidyl choline (lecithin) fractions were prepared from tuna, salmon, and menhaden muscle, from egg yolk, and from rat and beef liver. Hydrolysis by snake-venom phospholipase A (phosphatide acyl-hydrolase, EC 3.1.1.4) was used to determine the positional distribution of the fatty acids. The fatty acid composition of the hydrolyzed fatty acids (β position) and those remaining with the phosphatidyl moiety (α′ position) were separately determined by gas-liquid chromatography of the methyl esters. 36–86 mole % of the fatty acids esterified in the α′ position were saturated; 91–99 mole % of the fatty acids in the β position were unsaturated. Palmitic and stearic acids were the predominant saturated acids in the α′ position. Some similarity was noted in the β-position distribution of linoleic, arachidonic, eicosapentaenoic, docosaenoic, docosapentaenoic, and docosahexaenoic acids. This observation tends to support the hypothesis of the intechangeability of linoleic and arachidonic acids with “non-essential” polyenoic acids.