Isolation and Characterization of Multilayered Sheath Membrane Rich in Glucocerebroside from Shrimp Ventral Nerve

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Abstract
A membrane fraction rich in glucocerebroside was isolated from homogenates of ventral nerves of pink shrimp (Penaeus duorarum) by sucrose gradient centrifugation. The membrane fraction was observed at 0.15 M sucrose and was rich in lipids (lipid/protein ratio .apprx. 15:1). Electron microscopy showed that the fraction was derived from myelin-like multilayered glial membrane ensheathing axons, which has morphological similarities to myelin. Most of the lipids in shrimp nerve, including glucocerebroside, sphingomeylin, phosphatidylcholine, phosphatidylserine, phosphatidylethanolamine, and ethanolamine-plasmalogen, as well as cholesterol, appeared to be concentrated in this fraction. The fatty acids of these phospholipids were exclusively saturated or monounsaturated with C14.sbd.C26 chain lengths. The aldehyde moiety of plasmalogens contained only saturated C14.sbd.C18 carbon chains. Like glucocerebrosides, the sphingoid base of sphingomyelin consisted mainly of C14.sbd.C16 sphingenines and sphinganines, but they also contained significant amounts of C19 and C20 sphinganines. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the proteins in this fraction showed several bands in the 23,000-85,000 Mr range. Radioimmunoassay, however, did not show cross-reactivity with antibodies to myelin basic protein. The functional role of this membrane in relation to mammalian myelin is discussed.