Distribution of fatty acids in lipids of rat brain, brain mitochondria and microsomes

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Abstract
Lipids from rat brain homogenate, mitochondrial and microsomal fractions were analysed for P, total N, amino N, choline, cholesterol, acyl ester and aldehyde content. They were separated into lipid classes by silicic acid column chromatography. The distribution of fatty acids in whole lipids and the lipid classes was obtained by gas-chromatographic analysis of methyl esters of the fatty acids. Lipids from all three tissue fractions were similar in their content of different lipid classes and in the fatty acid distribution both in total-lipid extracts and in individual lipid classes. Proteolipids resembled total-lipid extracts in their fatty acid distribution. In comparison with other lipids, brain phospholipids are remarkable for their high content of saturated fatty acids (50%) and low proportion of essential (polyenoic) fatty acids (16%). Linoleic acid accounts for only 1% of total fatty acids. Mitochondria contained 26%, of their tissue dry weight as phospholipid, 6% as cholesterol and 4% as neutral fat. The composition of mitochondrial phospholipid was 32% of lecithin, 50% of phosphatidylserine and phosphatidylethanolamine, 13% of phosphoinositide, 2% of polyglycerophosphatide, 17% of plasma-logens (serine and ethanolamine). No lecithin plasmalogens were found. Fatty acids from total mitochondrial extract contained 28% of palmitic acid, 23% of stearic acid, 32% of oleic acid, 11% of essential acids (linoleic acid and polyenoic acids) and traces of short-chain acids (Cn < 16). Mitochondrial serine-ethanolamine phosphatide fraction contained 9% of palmitic acid, 32% of stearic acid, 30% of oleic acid and 23% of essential fatty acids. Mitochondrial lecithin fatty acids consisted of 39% of palmitic acid, 17% of stearic acid, 32% of oleic acid and 8% of essential fatty acids. Polyglycerophosphatide fraction contained 13% of palmitic acid, 21% of stearic acid, 19% of oleic acid, 25% of essential acids and 4% of short-chain acids. No close resemblance was found between the composition of any brain lipid class and similar lipids from other organs, but some general trends were apparent. The findings are discussed in connexion with possible metabolic functions of lipids.