The lipid composition of the salt (rectal) gland of spiny dogfish

Abstract

1. 1. The lipids from the salt (rectal) gland of spiny dogfish have been isolated and characterized. 2. 2. The major lipids were cholesterol, ethanolamine phosphoglycerides and choline phosphoglycerides. Other phospholipids were sphingomyelins, diphosphatidylglycerols, inositol phosphoglycerides and serine phosphoglycerides. The major fatty acid of ethanolamine phosphoglycerides was 22:6 with smaller amounts of 20:4, 18:1, 18:0 and 16:0. The major acids of choline phosphoglycerides were 16:0, 18:1, 20:4 and 22:6. 3. 3. The major glycosphingolipids were sulphatides and N-acetylneuraminylgalactosylglucosylceramides, and in addition there were minor amounts of glucosylceramides and galactosylceramides. 4. 4. The polar part of the sulphatides was galactose 3-sulphate. The fatty acids were mainly saturated and monounsaturated d-2-hydroxy C 22–C 24 acids. The longchain bases contained equal amounts of 1,3-dihydroxy-2-amino compounds and 1,3,4-trihydroxy-2-amino compounds with 16–20 carbon atoms. Bases with a methyl branch in Position 2, 3 or 4 from the methyl end were relatively abundant. The methyl branch was preferentially on carbon atom 16 as indicated from the polar end. 5. 5. The polar part of the choline phospholipids was phosphorylcholine exclusively. The sphingomyelin fatty acids were mainly normal C 14–C 24 acids with an unusually large amount of 22:1. A branched-chain 15:0 acid was identified, earlier unknown in sphingolipids of higher animals. All long-chain bases were dihydroxy bases with 15–19 carbon atoms. 6. 6. The unsaturation of paraffin chains was considerably higher among sphingolipids as well as glycerolipids of rectal gland of spiny dogfish (cold-blooded) than of salt gland of marine birds. Also, there was an unusually high amount of branched-chain components of sphingolipids of the rectal gland. These differences may be a prerequisite for an optimal liquid-crystalline state of the membrane. 7. 7. A role for sulphatides in Na + transport is indicated by a similar ratio of (Na +-K +)-ATPase and sulphatides in several tissues with increased transport capacity.