Molecular Species of Phospholipids with Very Long Chain Fatty Acids in Skin Fibroblasts of Zellweger Syndrome

The ratio of C_26:0/C_22:0 fatty acids in patient lipids is widely accepted as a critical clinical criterion of peroxisomal diseases, such as Zellweger syndrome and X-linked adrenoleukodystrophy (X-ALD). However, phospholipid molecular species with very long chain fatty acids (VLCFA) have not been precisely characterized. In the present study, the structures of such molecules in fibroblasts of Zellweger syndrome and X-ALD were examined using LC–ESI–MS/MS analysis. In fibroblasts from Zellweger patients, a large number of VLCFA-containing molecular species were detected in several phospholipid classes as well as neutral lipids, including triacylglycerol and cholesteryl esters. Among these lipids, phosphatidylcholine showed the most diversity in the structures of VLCFA-containing molecular species. Some VLCFA possessed longer carbon chains and/or larger number of double bonds than C_26:0-fatty acid (FA). Similar VLCFA were also found in other phospholipid classes, such as phosphatidylethanolamine and phosphatidylserine. In addition, VLCFA-containing phospholipid species showed some differences among fibroblasts from Zellweger patients. It appears that phospholipids with VLCFA, with or without double bonds, as well as C_26:0-FA might affect cellular functions, thus leading to the pathogenesis of peroxisomal diseases, such as Zellweger syndrome and X-ALD.     

Identification of n‐6 Monounsaturated Fatty Acids in Acer Seed Oils

Seed oils from Acer species are a potential source of the nutraceutical fatty acids, nervonic acid (cis‐15‐tetracosenoic acid, NA), and γ‐linolenic acid (cis‐6,9,12‐octadecatrienoic acid, GLA). To further characterize the genus, seed fatty acid content and composition were determined for 20 species of Acer. Fatty acid content ranged from 8.2% for Acer macrophyllum to over 36% for A. mono and A. negundo. The presence of very‐long‐chain fatty acids (VLCFA), with chain length of 20‐carbons or greater, and GLA were characteristic features of the seed oils. In all species, erucic acid (cis‐13‐docosenoic acid, EA) was the predominant VLCFA with the highest level of NA being only 8.6% in A. olivianum. Regioselective lipase digestion demonstrated that VLCFA are largely absent from the sn‐2 position of seed triacylglycerol, whereas GLA is primarily located at this position. Five Acer species contained low levels (<2%) of cis‐12‐octadecenoic acid and cis‐14‐eicosenoic acid, uncommon n‐6 fatty acids not previously reported from Acer.     

Identification and Characterization of Phospholipids with Very Long Chain Fatty Acids in Brewer’s Yeast

Yeast lipids and fatty acids (FA) were analyzed in Saccharomyces pastorianus from seven breweries and in the dietary yeast supplement Pangamin. GC–MS identified more than 30 FA, half of which were very‐long chain fatty acids (VLCFA) with hydrocarbon chain lengths of ≥22 C atoms. Positional isomers ω‐9 and ω‐7 were identified in FA with C18–C28 even‐numbered alkyl chains. The most abundant ω‐7 isomer was cis‐vaccenic acid. The structure of monounsaturated FA was proved by dimethyl disulfide adducts (position of double bonds and cis geometric configuration) and by GC–MS of pyridyl carbinol esters. Ultra‐high performance liquid chromatography‐tandem mass spectrometry with negative electrospray ionization identified the phospholipids phosphatidylethanolamine, phosphatidylinositol and phosphatidylcholine, with more than 150 molecular species. Wild‐type unmutated brewer's yeast strains conventionally used for the manufacture of food supplements were found to contain VLCFA.     

Stereospecific analysis of glycerolipids of egg yolk of Japanese quail (Coturnix coturnix japonica)

Phosphatidylcholine, phosphatidylethanolamine and triacylglycerol were isolated from egg yolk of the Japanese quail. Fatty acid compositions at the two and three positions of glycerol in the glycerolipids were determined by stereospecific analysis employing phospholipase A₂. The distribution of the total number of carbon atoms in the fatty acid moieties of triacylglycerol was also quantitated by high temperature gas liquid chromatography. The distribution of acyl groups in each of the positions of the phosphatidylcholine, phosphatidylethanolamine and triacylglycerol was not random, and each position has a characteristic composition. The phosphatidylcholine and phosphatidylethanolamine had distinctive fatty acid distributions for positionsn-2 of the triacylglycerol had a predominance of unsaturated fatty acids of which 18∶1 (69.9%) was the major component. Positionsn-3 contained 49.3% saturated fatty acids and was more saturated than positionsn-1 by 8.1%. The experimentally determined distribution of the carbon numbers in triacyl glycerol deviated significantly from the distribution predicted by 1-random-2-random-3-random association of the fatty acids. The data suggest that in Japanese quail there is marked preferencial synthesis of some triacylglycerols.     

Elucidation of Phosphatidylcholine Composition in Krill Oil Extracted from <Emphasis Type="Italic">Euphausia superba</Emphasis>

High performance liquid chromatography-electrospray tandem mass spectrometry was used to elucidate the phospholipids in krill oil extracted from Euphausia superba, an emerging source for human nutritional supplements. The study was carried out in order to map the species of the choline-containing phospholipid classes: phosphatidylcholine and lyso-phosphatidylcholine. In addition, the prevalent phosphatidylcholine class was quantified and the results compared with prior analysis. The qualification was performed with separation on a reverse phase chromatography column, while the quantification was obtained with class separation on a normal phase chromatography column. An Orbitrap system was used for the detection, and pulsed-Q dissociation fragmentation was utilized for the identification of the species. An asymmetrical exclusion list was applied for detection of phospholipid species of lower concentration, significantly improving the number of species observed. A total of 69 choline-containing phospholipids were detected, whereof 60 phosphatidylcholine substances, among others seven with probable omega-3 fatty acids in both sn-1 and sn-2. The phosphatidylcholine concentration was estimated to be 34 ± 5 g/100 g oil (n = 5). These results confirm the complexity of the phospholipid composition of krill oil, and the presence of long chained, heavily unsaturated fatty acids.     

The lipid composition of microsomal preparations from lactating bovine mammary tissue

The microsomes isolated from lactating bovine mammary tissue contained 4.3 mg lipid per milligram nitrogen. Phospholipids comprised 83% of the lipids. The neutral lipids were composed of triglycerides (20–30%), diglycerides (5–10%), free fatty acids (15–30%, cholesterol (35–40% and cholesterol esters (10–12%, respectively. Phosphatidylcholine was the predominant phospholipid component (>50%), and the remainder consisted of phosphatidylethanolamine (21–13%), phosphatidylserine (4–6%), phosphatidylinositol (8%), sphingomyelin (9%) and lysophosphatidylcholine (2%) respectively. The composition of the microsomal phospholipids was similar to that of isolated mammary cells and tissue homogenates but quite different from milk and fat globule membrane phospholipids. The triglycerides contained short chain fatty acids but their relative concentrations were lower than in milk triglycerides. The various lipid fractions had a variable proportion of saturated fatty acids, i.e., triglycerides (47.7%), diglycerides (86.7%), free fatty acids (70.6%), phosphatidylcholine (50.6%), phosphatidylethanolamine (50.8%), phosphatidylserine (35.3%), phosphatidylinositol (40.5%) and sphingomyelin (82.3%), respectively. The molecular distribution of fatty acids in the microsomal triglycerides and phosphatidylcholine was similar to that occurring in milk, i.e., the short chain and unsaturated fatty acids were concentrated in the primary positions (sn1 andsn3) of the triglycerides, and the unsaturated acids were preferentially located in positionsn2 of the phosphatidylcholine. The compositional data indicate that mammary microsomes are not the direct source of the phospholipids of the milk fat globule.     

Fatty Acid and Lipid Profiles with Emphasis on n-3 Fatty Acids and Phospholipids from Ciona intestinalis

In order to establish Ciona intestinalis as a new bioresource for n‐3 fatty acids‐rich marine lipids, the animal was fractionated into tunic and inner body tissues prior to lipid extraction. The lipids obtained were further classified into neutral lipids (NL), glycolipids (GL) and phospholipids (PL) followed by qualitative and quantitative analysis using GC‐FID, GC–MS, ¹H NMR, 2D NMR, MALDI‐TOF‐MS and LC–ESI–MS methods. It was found that the tunic and inner body tissues contained 3.42–4.08 % and 15.9–23.4 % of lipids respectively. PL was the dominant lipid class (42–60 %) irrespective of the anatomic fractions. From all lipid fractions and classes, the major fatty acids were 16:0, 18:1n‐9, C20:1n‐9, C20:5n‐3 (EPA) and C22:6n‐3 (DHA). The highest amounts of long chain n‐3 fatty acids, mainly EPA and DHA, were located in PL from both body fractions. Cholestanol and cholesterol were the dominant sterols together with noticeable amounts of stellasterol, 22 (Z)‐dehydrocholesterol and lathosterol. Several other identified and two yet unidentified sterols were observed for the first time from C. intestinalis. Different molecular species of phosphatidylcholine (34 species), sphingomyelin (2 species), phosphatidylethanolamine (2 species), phosphatidylserine (10 species), phosphatidylglycerol (9 species), ceramide (38 species) and lysophospholipid (5 species) were identified, representing the most systematic PL profiling knowledge so far for the animal. It could be concluded that C. intestinalis lipids should be a good alternative for fish oil with high contents of n‐3 fatty acids. The lipids would be more bioavailable due to the presence of the fatty acids being mainly in the form of PL.     

Phospholipid fatty acid composition and stereospecific distribution of soybeans with a wide range of fatty acid composition

Phospholipid (PL) fatty acid composition and stereospecific distribution of 25 genetically modified soybean lines with a wide range of compositions were determined by gas chromatography and phospholipase A₂ hydrolysis. Pl contained an average of 55.3% phosphatidylcholine, 26.3% phosphatidylethanolamine, and 18.4% phosphatidylinositol. PL class proportions were affected by changes in overall fatty acid composition. PL fatty acid composition changed with oil fatty acid modification, especially for palmitate, stearate, and linolenate. Stereospecific analysis showed that saturated fatty acids were primarily located at the sn-1 position of all PL, and changes of the saturates in PL were largely reflected on this position. Oleate was distributed relatively equally between the sn-1 and sn-2 positions. Linoleate was much more concentrated on sn-2 than on sn-1 position for all PL. Linolenate was distributed relatively equally at low concentration but preferred sn-2 position at high concentration.     

Regiospecific distribution of fatty acids in triacylglycerols and phospholipids from broad beans (Vicia faba)

Regiospecific distributions of fatty acids of triacylglycerols (TAG) and phospholipids (PL) separated from broad beans (Vicia faba) of four cultivars (Minpo, Sanuki, Nintoku and Sanren) were investigated. The major lipid components were PL (47.5–50.5 wt‐%) and TAG (47.7–50.1 wt‐%), while steryl esters, hydrocarbons, free fatty acids, diacylglycerols and monoacylglycerols were present in minor proportions (1.6–2.4 wt‐%). The PL components isolated from the four cultivars were phosphatidylcholine (56.4–58.4 wt‐%), phosphatidylethanolamine (20.3–21.7 wt‐%) and phosphatidylinositol (16.6–18.6 wt‐%). Phosphatidylinositol was unique in that it had the highest saturated fatty acid content among these PL. The principal characteristics of the fatty acid distribution in the TAG and PL were evident in the beans: Unsaturated fatty acids were predominantly concentrated in the sn‐2 position while saturated fatty acids primarily occupied the sn‐1 or sn‐3 position in these lipids. The lipid components and fatty acid distributions were almost the same in the four cultivars and were not influenced by genetic variability and planting location. These results could be useful information to both consumers and producers for the manufacture of traditional broad bean foods in Japan.     

Lipidomic Study of Precursors of Endocannabinoids in Freshwater Bryozoan Pectinatella magnifica

Freshwater bryozoan Pectinatella magnifica was collected from a sand pit (South Bohemia). The total lipids after extraction from lyophilized bryozoans were analyzed using high‐performance liquid chromatography/high‐resolution negative tandem electrospray mass spectrometry. A total of 19 lipid classes were identified, including N‐acyl‐substituted phospholipids, that is, N‐acylphosphatidylethanolamine and N‐acylphosphatidylserine in their plasmenyl forms. Based on gas chromatography/mass spectrometry of 3‐pyridylcarbonyl (picolinyl) esters, a very unusual fatty acid was identified, namely 24:7n‐3 (all‐cis‐3,6,9,12,15,18,21‐tetracosaheptaenoic acid). The presence of polyunsaturated fatty acids in individual classes is very specific: arachidonic and eicosapentaenoic acids being predominantly bound as amides in N‐acyl phospholipids, that is, diacyl‐N‐acylphosphatidylethanolamines (NAPtdEtn), plasmenyl‐N‐acylphosphatidyl ethanolamines (PlsNAPtdEtn), diacyl‐N‐acylphosphatidylserines (NAPtdSer), and plasmenyl‐N‐acylphosphatidylserines (PlsNAPtdSer). While 24:6n‐3 was identified in the sn‐2 position of several phospholipids, 24:7n‐3 was identified in only two plasmalogens, that is, PlsNAPtdEtn and PlsNAPtdSer. Thanks to the tandem mass spectrometry, we managed to identify the position of all acyl groups in both diacyl‐ and also in alkenyl‐acyl‐(plasmenyl) molecular species of N‐acylphospholipids. The identification of the molecular species of N‐acyl‐substituted phosphatidylethanolamine and phosphatidylserine, including their plasmalogen forms, in the freshwater bryozoan P. magnifica has enabled the identification of endogenous cannabinoid precursors.     

Generation and remodeling of highly polyunsaturated molecular species of rat hepatocyte phospholipids

Freshly isolated rat hepatocytes were incubated for 20 min with [U-¹⁴C]glycerol in the presence or absence of unlabeled linoleic (18∶2n-6), arachidonic (20∶4n-6), or docosahexaenoic (22∶6n-3) acid, added as albumin complex in 10% ethanol. Most of the radioactivity (≈95%) recovered in hepatocyte lipids was present in phosphatidylcholine (PC), phosphatidylethanolamine (PF), and triacylglycerol (TAG). The presence of exogenous fatty acids resulted in (i) higher incorporation of [U-¹⁴C]glycerol, (ii) higher percentage of label in TAG, and (iii) enhanced formation of PC and PE molecular species bearing the exogenous fatty acid at both the sn-1 and sn-2 positions of glycerol. In each case, these molecular species contained 60 to 70% of the label in that lipid class. Further incubation of the cells for 40 and 80 min in the absence of labeled substrate and exogenous fatty acids resulted in a redistribution of label among PC and PE molecular species due to deacylation-reacylation at the sn-1 position of glycerol.     

Effect of radiotherapy and chemotherapy on composition of tumor membrane phospholipids

Phospholipid extracts were made of a murine mammary adenocarcinoma implanted in the dorsum of the foot of C3H/He mice before and 96 h after 17 Gy irradiation or 150 mg/kg cyclophosphamide. Extracts of untreated tumors, which had grown for a further 96 h, were also studied. Although previous studies have shown significant changes in the precursors and catabolites of phosphatidylcholine and phosphatidylethanolamine following therapy, ³¹P nuclear magnetic resonance analysis of extracts showed no changes in these membrane constituents and other observed phospholipid species. A significant decrease in 1-alkyl-2-acyl-sn-glycero-3-phosphocholine, however, was observed 96 h following cyclophosphamide treatment.     

Influences of subzero thermal acclimation on mitochondrial membrane composition of temperate zone marine bivalve mollusks

The phospholipid and phospholipid fatty acid composition of gill mitochondrial membranes from two temperate zone marine bivalve mollusks, the quahog, Mercenaria mercenaria, and the American oyster, Crassostrea virginica, were examined after acclimation to 12 and −1°C. Cardiolipin (CL) was the only phospholipid with proportions altered upon acclimation to −1°C, increasing 188% in the mitochondrial membranes of M. mercenaria. Although the ratio of bilayer stabilizing to destabilizing lipids is frequently associated with cold acclimation in ectothermic species, no change was found in this ratio in either of the species. Polyunsaturated fatty acids (PUFA) were found only to increase in C. virginica with cold acclimation, with total n-3 PUFA increasing in the phospholipid phosphatidylethanolamine, total n-6 PUFA increasing in CL, and total PUFA increasing in phosphatidylinositol. Monounsaturated fatty acids, not PUFA, were found to have increased in M. mercenaria, with 18:1n−9 increasing by 150% in CL, and 20∶1 increasing in both CL and phosphatidylcholine, by 146 and 192%, respectively. These manipulations of membrane phospholipid and fatty acid composition may represent an attempt by these species to help maintain membrane function at low temperatures.     

Activity of phospholipid-synthesizing enzymes in rat liver plasma membranes and the source of biliary lecithin

The potential for the synthesis of phosphatidylcholine by the bile canalicular membrane of the liver cell was assessed by measuring the activity of a number of phospholipid synthesizing enzymes in isolated bile canalicular membrane fractions from rat liver. The activity of these various enzymes was compared to that present in noncanalicular liver cell plasma membranes and in microsomes. The CDP-choline: 1,2-diacyl-sn-glycerol-cholinephosphotransferase was virtually absent from the bile canalicular membranes but the specific activities of S-adenosyl-L-methionine:phosphatidylethanolamine N-methyltransferase and acyl-CoA:1-acyl-sn-glycero-3-phosphoryl-choline acyltransferase were 11–15% of those found in the microsomes. The bile canalicular membranes also contained detectable acyl-CoA:sn-glycero-3-phosphate acyltransferase activity and the ability to potentiate the Ca⁺⁺-stimulated exchange of bases between different phospholipids. These findings indicate that the bile canalicular membranes have a very limited capacity for the formation of phosphatidylcholine under the assay conditions employed. A preliminary report of this paper was given at the AOCS Spring Meeting, Dallas, April 1975.     

Lipid remodeling in mouse liver and plasma resulting from Δ6 fatty acid desaturase inhibition

Electrospray/tandem mass spectrometry was used to quantify lipid remodeling in mouse liver and plasma during inhibition of polyunsaturated fatty acid synthesis by the Δ6 fatty acid desaturase inhibitor, SC-26196. SC-26196 caused increases in linoleic acid and corresponding decreases in arachidonic acid and docosahexaenoic acid in select molecular species of phosphatidylcholine, phosphatidylethanolamine, and cholesterol esters but not in phosphatidylserine, phosphatidylinositol, or triglycerides. For linoleic acid-, arachidonic acid-, and docosahexaenoic acid-containing phospholipid species, this difference was, in part, determined by the fatty acid at the sn-1 position, namely, palmitic or stearic acid. An understanding of phospholipid remodeling mediated by Δ6 desaturase inhibition should aid in clarifying the contribution of arachidonic acid derived via de novo synthesis or obtained directly in the diet during inflammatory responses.     

Preparation of n‐3 Polyunsaturated Phosphatidylglycerol from Salmon Roe Lipids by Phospholipase D and In Vitro Digestion

Phosphatidylglycerol (PG) is a highly functional phospholipid (PL), which has many physiological functions. However, naturally occurring PG binding n‐3 polyunsaturated fatty acid (n‐3 PUFA) is low in content, resulting in a scarcity of industrial bio‐resources of n‐3 PUFA enriched PG. The current study investigates the preparation of salmon roe PG (SRPG) from three types of salmon roe lipids and glycerol via phospholipase D (PLD)‐mediated transphosphatidylation. The yields of SRPG obtained from salmon roe total lipid (SRTL) and salmon roe PL (SRPL) are higher than those obtained from purified salmon roe phosphatidylcholine (SRPC) in aqueous system. Following a 24 h reaction with 0.75 U PLD, SRTL, and SRPL yield up to 96.4 mol% and 96.7 mol% SRPG, respectively. In addition, more fatty acids are released from synthesized SRPG via hydrolysis by pancreatic enzymes than from SRPC and soybean PC in in vitro digestion model. Fatty acids at the sn‐2 position of SRPG are completely liberated by 0.04 U of phospholipase A₂ (PLA₂) during a 6 h reaction, whereas fatty acids of SRPC are partially unhydrolyzed even after a 24 h reaction. Our results suggest that SRPG converted from salmon lipids by PLD is a functional PL with high bioavailability of n‐3 PUFAs. Practical Applications: Phosphatidylglycerol rich in n‐3 PUFAs is prepared from salmon roe lipids (SRPG) catalyzed by PLD. The SRPG yields reach 96.4 mol% and 96.7 mol% of phosphatidylcholine contained in SRTL and SRPL, respectively, in aqueous reaction system. Fatty acids rich in n‐3 PUFAs at sn‐2 position of prepared SRPG are rapidly liberated by PLA₂ in an in vitro digestion model.     

Molecular species composition of phosphatidylcholines during the development of the avian embryo brain

A comparative approach has been used to investigate the molecular species composition of phosphatidylcholine (PC) and its age variation throughout several developmental stages of chick and duck embryo brains. The brain PC consist of 15 major molecular species which do not undergo appreciable variation in their relative abundance either during embryonic development or between equivalent stages of maturation in the 2 avian species. In fact, a highly invariable molecular architecture of PC is shown in the developing organ. Molecular species containing saturated or monounsaturated fatty acids were dominant in all stages of development of the avian embryo brain. Among these molecular species, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine accounted for 75–80% of the total PC.     

Enzymatic Synthesis of 1‐Alkyl‐2‐hydroxy‐sn‐glycero‐2,3‐cyclic‐phosphate Using a Novel Lysoplasmalogen‐Specific Phopholipase D

Many phospholipase Ds (PLDs) are known to catalyze transphosphatidylation as well as hydrolysis of phospholipids. Transphosphatidylation of lysoplasmalogen (LyPls)‐specific phospholipase D (LyPls‐PLD), which catalyzes hydrolysis of ether lysophospholipids such as LyPls and 1‐hexadecyl‐2‐hydroxy‐sn‐glycero‐3‐phosphocholine (Lyso‐PAF), still remains unclear. This study aims to reveal the transphosphatidylation activity of LyPls‐PLD, that is, the production of cyclic ether lysophospholipid. The enzymatic reaction is conducted in a buffer system, and the reaction products of a novel LyPls‐PLD from Thermocrispum sp. are investigated using mass spectrometry (MS). MS analyses demonstrate the reaction products to consist of 100% 1‐hexadecyl‐2‐hydroxy‐sn‐glycero‐2,3‐cyclic‐phosphate (cLyPA) and choline from Lyso‐PAF; however, 1‐alkenyl‐2‐hydroxy‐sn‐glycero‐2,3‐cyclic‐phosphate from 1‐O‐1′‐(Z)‐octadecenyl‐2‐hydroxy‐sn‐glycero‐3‐phosphocholine and 1‐O‐1′‐(Z)‐octadecenyl‐2‐hydroxy‐sn‐glycero‐3‐phosphoethanolamine is not produced. These results are expected to help in elucidating the catalytic mechanism of LyPls‐PLD, that is, the rate‐limiting step, and indicate LyPls‐PLD to be useful for the one‐pot synthesis of cLyPA. Practical Applications: A novel phospholipase D, LyPls‐PLD, can exclusively synthesize cLyPA from Lyso‐PAF using a one‐step enzymatic reaction without an organic solvent. cLyPA could be expected to show bioactivities similar to those of cyclic phosphatidic acid, which promotes normal cell differentiation, hyaluronic acid synthesis, antiproliferative activity in fibroblasts, and inhibitory activity toward cancer cell invasion and metastasis.     

Phospholipid molecular species composition of developing fetal guinea pig brain

Adequate accumulation of polyunsaturated essential fatty acids, in particular docosahexaenoic acid (22∶6n−3), into membrane phospholipids is critical for optimal fetal brain development. This process is maximal during the period of rapid neurite outgrowth, neuritogenesis, which precedes the major growth phase, myelination. There is no information about differential changes during gestation to individual brain phospholipid molecular species which contain 22∶6n−3. Such details of brain development would be concealed by total fatty acid analysis of isolated phospholipid classes. We have detailed phosphatidylcholine (PC) and phosphatidylethanolamine (PE) molecular species compositions in developing fetal guinea pig brain. Total brain PC concentration increased substantially between 40 and 68 (term) d of gestation, corresponding to myelination, while PE increased in a biphasic manner between 25–35 d, which was coincident with onset of neuritogenesis, and 40–68 d. Fetal brain development was accompanied by complex changes in the concentration of individual phospholipid molecular species. During early gestation (25–40 d) 22∶6n−3 was enriched in both PC and PEsn−1 16∶0 molecular species. However, between 40 d and term there was no further increase in brain PC 22∶6n−3 content, while brain PE was significantly enriched in both PE 18∶1/22∶6 and PE18∶0/22∶6. We hypothesize that accumulation of 22∶6n−3 intosn−1 18∶1 and 18∶0 species represents establishment of a 22∶6n−3-containing membrane PE pool which may be turned over more slowly thansn−1 16∶0 species. Identification of specific changes in membrane phospholipids which are associated with defined events in brain development may provide a basis for assigning functional roles to individual molecular species.     

Mitochondrial membrane composition of two arctic marine bivalve mollusks, Serripes groenlandicus and Mya truncata

The phospholipid and fatty acid composition of gill mitochondria membranes from two Arctic marine bivalve mollusks, Mya truncata and Serripes groenlandicus, were examined. These animals were collected from the Arctic Ocean, where waters remain below 0°C throughout the year. In both species, the primary membrane phospholipids were phosphatidylcholine, and phosphatidylethanolamine. Although a low ratio of bilayer-stabilizing phospholipids to bilayer-destabilizing phospholipids is frequently associated with cold acclimation in temperate species, this ratio is very different between the two species. The monounsaturated fatty acid 20∶1 was abundant in the membranes of both Arctic species equaling 13.0% of the fatty acid composition in S. groenlandicus, and 17.7% in M. truncata. Polyunsaturated fatty acids were relatively low in the Arctic species, equaling 35.9% of total membrane fatty acids compared to that of temperate zone mollusks. It is suggested that monoenes are common in the tissues of Arctic species since they play a role in maintaining membrane function at subzero temperatures.