1. 1. Control and essential fatty acid deficient rats were injected with [Me-14C]-methionine and killed at intervals up to 5 h afterwards. Incorporation of the methyl label was then compared in monoene, diene, triene, tetraene and higher polyun-saturated fatty acid fractions of their liver choline phosphatides. 2. 2. The essential fatty acid deficiency increased oleic and eicosatrienoic acids and decreased linoleic and arachidonic acid in both the ethanolamine and choline phosphatides. The rate and extent of methyl incorporation into the total phosphatidylchohne were similar for both groups. 3. 3. In control rats, the predominant phosphatidylcholine fractions were tetraene (54% of total) and diene (28% of total). About 10% of the phosphatidylcholines was a highly unsaturated fraction containing mainly 22:5 and 22:6 fatty acids. The predominant phosphatidylcholine fractions in essential fatty acid deficiency were monoene (41% of total) and triene (38% of total) with the diene and tetraene fractions representing about 10% each of the total phosphatidylcholines. Fatty acid compositions suggested similar changes probably occurred in the major fractions of the phosphatidylethanolamines. 4. 4. Control rats incorporated methyl mainly into their tetraene and diene fractions, whereas deficient animals had most of the label in their monoene and triene fractions. The type of unsaturated fatty acid on the phosphatidylethanolamine substrate seemed much less of an influence on its methylation to phosphatidylcholine than was the concentration of a particular phosphatidylethanolamine fraction. 5. 5. A phosphatidylcholine fraction containing penta- and hexaene fatty acids appeared to be more active metabolically than did the phosphatidylcholine fractions having fatty acids with less unsaturation. © 1969.
