Ether glycerolipids: novel substrates for studying specificity of enzymes involved in glycerolipid biosynthesis in higher plants

Abstract

Ether glycerolipids, predominantly alkylacylglycerols and alkylacylglycerophosphocholines, are synthesized in photomixotrophc rape (Brassica napus) suspension cells from various exogenous monoalkylglycerols. The stereospecific distribution of acyl moieties was studied in these ether glycerolipids with regard to chain-length and degree of unsaturation of alkyl moieties and compared with the distribution of acyl moieties in the corresponding endogenous acyl glycerolipids. The results show the following : (1) Alkylacylglycerophosphocholines replaced up to one-half of the corresponding physiological membrane lipids, i.e. diacylglycerophosphocholines, without changing the total amount of cholineglycerophospholipids as compared to untreated cells. (2) The composition of acyl moieties in total lipids of rape cells was practically unaltered by fatty acids derived via oxidative cleavage from the various alkyl moieties of ether glycerolipids. (3) In 1-0-alkyl-2-acylglycerols derived from exogenous alkylglycerols and in endogenous 1,2-diacylglycerols compositions of acyl moieties were found to be different indicating that different pathways were operative in the biosynthesis of these two neutral glycerolipids. (4) Enzymes involved in synthesizing molecular species of I-0-alkyl-2-acylglycerophosphocholines or 2-O-alkyl-lacylglycerophosphocholines as well as 1,2-diacylglycerophosphocholines showed similar specificities with regard to chain-length and degree of unsaturation of both alkyl and corresponding acyl moieties. Thus, ether glycerolipids formed by plant cells from exogenous alkylglycerols are suitable metabolites for studying the specificity of enzymes involved in the biosynthesis of glyerolipids.Higher plants do not contain appreciable amounts of ether lipids [l -31. Yet, plant cells and plant cell microsomes are able to synthesize ether glycerolipids from suitable exogenous precursors [4-71. Thus, rape (Brassica napus) cells in culture have been found to convert exogenous 1 -0-alkylglycerols predominantly to l-O-alkyl-2-acylglycerols, 1-0-alkyl-3-acylglycerols and 1 -O-alkyl-2-acylglycerophosphocholines [8, 91. The alkyl moieties of ether glycerolipids have been found to be metabolically quite stable, as compared to the corresponding acyl moieties of acyl glycerolipids [lo]. Therefore, lipids containing alkyl moieties, rather than those containing only acyl moieties, may be useful as markers in studies on the biosynthesis and turnover of glycerolipids in plant cells. Using alkylglycerols as substrates we have studied the stereospecificity of enzymes involved in the formation of complex glycerolipids. MATERIALS AND METHODSChemicals and syntheses rac-1-0-Alkylglycerols were prepared following established procedures [I 1, 121. Similarly,

Stereospecific synthesis of ether and thioether phospholipids. The use of L-glyceric acid as a chiral phospholipid precursor

“…ch3 2 a number of human cancer cells.11 The lead compound (1) appeared to fulfill the criteria attributed to effective antitumor activity100 in possessing (1) an alkyl moiety at the sn-l-position, (2) a PAF-hydrolase resistant short-chain substituent at the sn-2-position,17 and (3) a phosphocholine function at the sn-3-position of glycerol.…”

“…1986, 29, 2114-2117. (12) (1) simplicity and efficiency, (2) flexibility with respect to the substituent groups that can be introduced, and (3) applicability to the development of specific ether and thioether phospholipid analogues with the desired target structures for biological and physicochemical studies. Synthetic work along these lines is currently under way in our laboratory.…”

Alterations of soybean lecithin during curd formation in cheese making

“…Stereospecific Analysis of Acyl Moieties at the sn-1 and sn -2 Positions of Diacylglycerophosphocholines and Diacylglycerophosphoethanolamines. About 2 mg of the two glycerophospholipids from curd and whey were hydrolyzed with phospholipase A2 from hog pancreas (Boehringer Mannheim, D-6800 Mannheim, FRG) and analyzed as described earlier (Weber and Benning, 1985).…”