Structure and metabolism of phospholipids in bovine epididymal spermatozoa

Abstract

Lipid analysis of bovine epididymal spermatozoa showed relatively large amounts of alkylacyl- and alk-1-enylacylglycerols in their choline and ethanolamine phospholipids and alkylacylglycerol as the major constituent of a glycolipid tentatively identified as a monogalactosyl sulfate. The ether lipids exhibited remarkably simple molecular structures i.e., the phospholipids had only 16:0 as alkyl and alk-1-enyl groups and their constituent fatty acids were almost exclusively 22: 5 ( n−6) and 22: 6 ( n−3). The glycolipid had mainly 16:0 as both alkyl and acyl moieties. In contrast, the diacyl choline and ethanolamine phosphoglycerides exhibited a much more complex fatty acid composition. 1,2-Diacylglycerols were the major nonpolar glycerolipid class and their acyl groups consisted almost exclusively of 14: 0, 16: 0 and 18: 0. Labeled glycerol and dihydroxyacetone added to the incubation medium were readily incorporated into sperm lipids under both aerobic and anaerobic conditions. In each case, diacylcholine phosphoglycerides, diacylglycerols and phosphatidic acid were the major labeled lipids. Distribution of label among the molecular species of diacylglycerols and choline phosphoglycerides resembled somewhat their natural abundance. No radioactivity was found in alkylacyl or alk-1-enylacyl glycerolipids. The ether lipids may provide stable structural components of sperm membrane while the diacyl analogs undergo degradation and resynthesis.