Formation of ether lipids and wax esters in mammalian cells Specificity of enzymes with regard to carbon chains of substrates

Abstract

The incorporation of radioactivity from individual constituents of an equimolar mixture of saturated straight-chain alcohols (14:0, 16:0, 18:0, 20:0) and of nearly uniform mixtures of isomeric cis- or trans-octadecenols ( Δ 8- Δ 16) into alkyl, alk-1-enyl and acyl moieties of diradylglycerophosphocholines and diradylglycerophosphoethanolamines and into alkyl and acyl moieties of wax esters was studied in rat brain as well as in L 1210 and S 180 ascites cells. The pattern of incorporation of radioactivity from the substrates into alkyl and alk-1-enyl moieties of ether phospholipids and into alkyl moieties of wax esters reveals the following: 1. (1) The enzymes catalyzing the biosynthesis of alkylacylglycerols, the common intermediates of cholinephospholipids and ethanolaminephospholipids, have no substrate specificity with regard to position of the double bond of either cis- or trans-octadecenols or of intermediate ether lipids derived therefrom. 2. (2) CDPcholine:diradylglycerol cholinephosphotransferases exhibit a strong preference for alkylacylglycerols with cis-8, cis-9 and cis-10-octadecenyl moieties, but no preference for the double bond position in the trans-octadecenylacylglycerols. 3. (3) CDPethanolamine:diradylglycerol ethanolaminephosphotransferases have no substrate specificity with regard to position of the double bond in cis- or trans-octadecenyl moieties of alkylacylglycerols. 4. (4) The enzyme systems catalyzing the biosynthesis of alkylacylglycerophosphocholines and alkylacylglycerophosphoethanolamines exhibit substrate specificity with regard to chain-length of saturated alcohols and intermediate ether lipids derived therefrom. 5. (5) Alkylacylglycerophosphoethanolamine desaturase and 6. (6) wax ester synthase are highly specific for alkylacylglycerophosphoethanolamines and long-chain alcohols, respectively, with regard to chain-length of saturated alkyl moieties, but not with regard to position of double bonds of cis- or trans-octadecenyl moieties.