Abstract
Summary Subcellular fractions of rat brain were prepared by differential and sucrose density gradient centrifugation and examined for their lipid composition. Two fractions, retained by 0.9 and 1.0 M sucrose, respectively, had the morphological characteristics of synaptic membranes. The former was characterized by a high concentration of serine phosphoglyceride. The lipids (sphingomyelin excepted) of both synaptic membrane fractions differed from the lipids of myelin and mitochondria in that fatty acids had shorter chain lengths and lesser degrees of unsaturation. Charged phospholipids may play a role in attracting soluble enzymes to membrane fractions. An example is the high relative specific activity of carboxylic ester hydrolases and acetylcholinesterase in synaptic membranes. The data suggest that the short chain length of fatty acids in synaptic membranes militates against strong London-van der Waals forces, while the high concentration of serine phosphoglyceride in membranes retained by 0.9 M sucrose promotes ionic interaction and formation of phospholipid-enzyme complexes.
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