The Lipid Composition of Rat CNS Axolemma‐enriched Fractions

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Abstract
The lipid composition is reported for rat CNS axolemma‐enriched membrane fractions isolated from rat CNS white matter via a purified preparation of myelinated axons. The more dense axolemma‐enriched fraction is 51.5% lipid, comprised of 21.3% cholesterol, 11.3% galactolipid (cerebrosides and sulfatides in a molar ratio of 1.3:1.0), 24.2% ethanolamine glycerophospholipid (41.0% in the plasmalogen form), 27.8% choline glycerophospholipid (14.7% in the plasmalogen form), 5.3% serine glycerophospholipid, 2.8% inositol glycerophospholipid, and 2.0% sphingomyelin. The less dense axolemma‐enriched fraction has a lipid composition that is intermediate between that of the more dense axolemma‐enriched fraction and the concomitantly isolated myelin; this myelin has a lipid composition consistent with that previously reported for myelin isolated by an alternative procedure. A concomitantly isolated and operationally defined myelin‐free axon fraction has a lipid composition distinct from that which we have previously reported for a rat CNS myelin‐free axon preparation. The more dense axolemma‐enriched fraction contains 11.94 μg ganglioside NeuNAc per mg dry weight in contrast to the myelin fraction, which contains 0.88 μg ganglioside NeuNAc per mg dry weight, This axolemma‐enriched fraction contains all the major brain‐type gangliosides, while myelin contains mostly ganglioside GMI. The lipid composition of these fractions is compared with that of other neuronal and axolemmal preparations. The origin and function of the axolemmal glycolipid are discussed.

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