Positional specificity in the incorporation of isomeric cis- and trans-octadecenoic acids into glycerolipids of cultured soya cells

Broad Separation of Isomeric Lipids by High-Resolution Differential Ion Mobility Spectrometry with Tandem Mass Spectrometry

Maturation of metabolomics has brought a deeper appreciation for the importance of isomeric identity of lipids to their biological role, mirroring that for proteoforms in proteomics. However, full characterization of the lipid isomerism has been thwarted by paucity of rapid and effective analytical tools. A novel approach is ion mobility spectrometry (IMS) and particularly differential or field asymmetric waveform IMS (FAIMS) at high electric fields, which is more orthogonal to mass spectrometry. Here we broadly explore the power of FAIMS to separate lipid isomers, and find a ~75% success rate across the four major types of glycero- and phospho- lipids (sn, chain length, double bond position, and cis/trans). The resolved isomers were identified using standards, and (for the first two types) tandem mass spectrometry. These results demonstrate the general merit of incorporating high-resolution FAIMS into lipidomic analyses. Graphical Abstract ᅟ.

Biosynthesis of storage lipids in plant cell and embryo cultures

The biosynthesis of storage lipids in plant cell and embryo cultures is discussed in the light of their significance in the breeding of agriculturally important oil seed crops. After a short introduction to the biosynthesis of storage lipids, i.e. triacylglycerols and wax esters, this review covers the occurrence and biosynthesis of storage lipids in plant cell and embryo cultures. Plant cells in culture generally contain low levels of both unusual fatty acids and triacylglycerols indicating that these cells are quite different from cells of oil storage tissues. There are a few exceptions to this rule which demonstrate that induction of genes involved in the expression of fatty acid modification and triacylglycerol assembly is possible in plant cell cultures. Such biosynthetically active plant cells may be of particular interest in future studies of storage lipid assembly. Both somatic and gametophytic embryos of oil plants exhibit high capacities for storage lipid biosynthesis and accumulation in vitro compared to cultured plant cells. Above all, the microspore-derived embryo system is recommended to both plant breeders and plant biochemists for the selection and multiplication of plants of superior quality.

Biosynthesis and biotransformation of ether lipids

Some naturally occurring as well as synthetic ether lipids are biologically active. In certain cases, the effects of these substances are enhanced, in others, they are inhibited by compounds that were isolated from natural sources or prepared by chemical synthesis. The biotransformation of natural or "unnatural" ether lipids in microorganisms, plant or animal tissue also can lead to substances that elicit biological effects. The production of such compounds through various biotechnological techniques is a field wide open for future exploration. In addition to animal cell cultures, plant cell cultures may become useful tools in biomedical studies concerned with ether lipids.

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

Ether glycerolipids, predominantly alkylacylglycerols and alkylacylglycerophosphocholines, are synthesized in photomixotrophic 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 either glycerolipids. (3) In 1-O-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 1-O-alkyl-2-acylglycerophosphocholines or 2-O-alkyl-1-acylglycerophosphocholines 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.

Formation of complex ether lipids from 1-O-alkylglycerols in cell suspension cultures of rape

Photomixotrophic cell suspension cultures of rape, Brassica napus, were incubated with rac-1-O-[1'-(14)C]hexadecylglycerol. Radioactivity was incorporated predominantly into choline glycerophospholipids. Prolonged incubation led also to considerable proportions of labeled ethanolamine glycerophospholipids. In addition to these ionic lipids,isomeric hexadecylacylglycerols as well as hexadecyldiacylglycerols were formed. About a third of the hexadecylglycerol supplied as substrate was cleaved within 48 h incubation. The palmitic acid formed by oxidative cleavage of the substrate was incorporated predominantly into choline glycerophospholipids, ethanolamine glycerophospholipids, and triacylglycerols. Incubation of an equimolar mixture of homologous saturated rac-1-O-[1'(14)C]alkylglycerols (C14, C16, C18, C20) with rape cells showed that alkylglycerols with alkyl moieties having 16 and 18 carbon atoms were incorporated preferentially. Incubation of labeled hexadecyglycerol with a homogenate of rape cells led also predominantly to choline glycerophospholipids; highest yields were obtained at pH 7. Neither the 1-O-alkyl moieties in choline glycerophospholipis nor those in ethanolamine glycerophospholipids were desaturated to 1-O-alk-1'-enylmoieties. The results of these experiments led to the following conclusions: (1) The acylation of 1-O-alkylglycerols to isomeric alkylacylglycerols is catalyzed by two acyltransferases differing in their specificity with regard to the chain length of the alkyl moiety in the substrate. (2) CDP-Choline: diacylglycerol cholinephosphotransferase and CDP-ethanolamine: diacylglycerol ethanolaminephosphotransferase are two enzymes differing in various respects. Cholinephosphotransferase exhibits a much higher affinity for 1-O-alkyl-2-O-acylglycerols than ethanolaminephosphotransferase. The two enzymes show marked differences with regard to their specificity for 1-O-alkyl-2-O-acylglycerols differing in the chain lengths of their alkyl moieties.

Metabolism of long-chain alcohols in cell suspension cultures of soya and rape

Heterotrophic cell suspension cultures of soya (Glycine max) and photomixotrophic cell suspension cultures of rape (Brassica napus) were incubated with cis-9-[1-(14)C]octadecenol for 3-48 h. It was found that under aerobic conditions large proportions of the alcohol are oxidized to oleic acid, which is incorporated predominantly into phospholipids, whereas up to 30% of the substrate is esterified to wax esters. This is true for both the heterotrophic and the photomixotrophic cell suspension cultures, but the metabolic rates are much higher in the latter. Under anaerobic conditions only small proportions of the radioactively labeled alcohol are oxidized to oleic acid, whereas a major portion of the alcohol is esterified to wax esters both in heterotrophic and photomixotrophic cultures. Incubations of homogenates of photomixotrophic rape cells with labeled cis-9-octadecenol showed that pH 6 is optimum for the formation of wax esters. This monounsaturated alcohol is preferred as a substrate over saturated longchain alcohols, whereas short-chain alcohols, cholesterol, and glycerol are not acylated. Incubations of an enzyme concentrate from a homogenate of rape cells with unlabeled cis-9-octadecenol and [1-(14)C]oleic acid, or [1-(14)C]stearoyl-CoA, or di[1-(14)C]palmitoyl-sn-glycero-3-phosphocholine showed that acylation of the longchain alcohol proceeds predominantly through acyl-CoA. Direct esterification of the alcohol with fatty acid as well as acyl transfer from diacylglycerophosphocholine could be demonstrated to occur to a much smaller extent.

Formation of (n-9) and (n-7) cis-monounsaturated fatty acids in seeds of higher plants

The relative abundance of (n-9) and (n-7) isomers in the monounsaturated fatty acids of seed lipids has been determined for selected plants in order to assess the biosynthetic reactions involved in their formation. Δ9 Desaturation of stearic acid to (n-9) octadecenoic acid is almost exclusively operative in the formation of monounsaturated fatty acids in the seeds of Helianthus annuus, Glycine max and Brassica napus, cv. Quinta and Erglu, in which chain elongation of monounsaturated fatty acids terminates at the level of an 18 carbon chain. Δ9 Desaturation of palmitic acid is a minor yet significant pathway in the seeds of Sinapis alba and Brassica napus, cv. Rapol and Tira, in which chain elongation of monounsaturated fatty acids occurs extensively beyond the 18 carbon chain. In each of these seeds, both (n-9) and (n-7) octadecenoic acids formed are subsequently elongated to icosenoic acids. However, elongation of the (n-7) isomer is terminated at the level of a 20 carbon chain, whereas the (n-9) icosenoic acid is selectively elongated to docosenoic acid and even up to tetracosenoic acid in Sinapis alba. Δ9 Desaturation of palmitic acid followed by elongation to (n-7) octadecenoic acid occurs to a minor extent in the seeds of Tropaeolum majus. Only the (n-9) octadecenoic acid, and not its (n-7) isomer, is elongated to icosenoic and docosenoic acids.