LIPID COMPOSITION OF SYNAPTIC PLASMA MEMBRANES ISOLATED FROM RAT BRAIN BY ZONAL CENTRIFUGATION

A plasma membrane fraction derived from rat brain nerve endings or the synaptic plasma membrane fraction, isolated by zonal centrifugation, was analyzed for their lipid content and their composition of lipid classes and their aliphatic moieties. With the exception of glycolipids and sphingomyelin, the lipid classes of synaptic plasma membrane are very similar to whole brain. Phosphatidylcholine and phosphatidylethanolamine are the major lipids and make up 62% of the total membrane lipid. Cholesterol and ceramide make up the major neutral lipids and 21 % of total brain lipid. The synaptic plasma membranes contain lower quantities of glyceryl ethers in phosphatidylethanolamine and phosphatidylcholine fractions than in whole brain. Certain distinctive features in fatty acid content were found; synaptic plasma membranes contained much less 18:1 acyl moieties in phosphatidylethanolamine and phosphatidylserine + phosphatidylinositol than found in whole brain, whereas most other acyl moieties with the exception of the longer chain unsaturated fatty acids are similar. The 22:6 acyl chains in synaptic plasma membrane account for approximately 32% of the total fatty acids in phosphatidylethanolamine and phosphatidylserine + phosphatidylinositol, but in whole brain the 22:6 fatty acids account for only about 26 and 20% of phosphatidylethanolamine and phosphatidylserine + phosphatidylinositol, respectively. The alk-1-enyl moieties in phosphatidylethanolamine are restricted to 16:0, 18:0, and 18:1 chain lengths in both synaptic plasma membrane and whole brain. © 1969, American Chemical Society. All rights reserved.