The Fatty Acid Composition of Individual Phospholipids from Rat Liver Nuclear Membrane and Nuclei*

The phospholipid distribution and the fatty acid composition of the individual phospholipids were determined for the nucleus and the bileaflet nuclear membrane. The phospholipid to protein ratio (milligram per mg) for the nuclear membrane was 0.45 and lipid phosphorus comprised 65% of the total membrane phosphorus. No significant differences were noted in the phospholipid composition of the nucleus and the nuclear membrane. The values for the nuclear membrane were phosphatidyl ethanolamine, 18.3 % ; phosphatidyl serine plus inositol, 13.8% ; phosphatidyl choline, 61.8% ; sphingomyelin, 2.5 % ; lysophosphatidyl choline, 1.4 % ; cardiolipin plus phosphatidic acid, 1.4 %. Differences between the nucleus and the nuclear membrane were detected in the fatty acid composition of the sphingomyelin, lysophosphatidyl choline, and phosphatidyl serine plus inositol fractions. These differences were confined largely to variations in the levels of fatty acids with carbon chain lengths of Czo and above. Phosphatidyl choline and phosphatidyl ethanolamine contained the highest levels of unsaturated fatty acids for both the nucleus (-53%) and nuclear membrane (-49%). The lowest degree of unsaturation for the nuclear membrane (23%) was found in sphingomyelin and lysophosphatidyl choline, while the minimum level of unsaturation for the nucleus (24%) was observed in lysophosphatidyl choline. Phosphatidyl serine plus inositol contained the largest amount of polyunsaturated fatty acids for both the nucleus (44%) and the nuclear membrane (33 %). A comparison of the fatty acid composition of the nuclear membrane phospholipids to the corresponding literature values for plasma membrane, golgi apparatus, and endoplasmic reticulum revealed major differences.