Composition and fatty acid content of rat ventral prostate phospholipids

The major phospholipids of rat ventral prostate have been separated and examined using thin-layer chromatography, gas chromatography and mass spectrometry. The main phospholipid classes were choline and ethanolamine glycerophospholipids, accounting for 77.9% of total lipid phosphorus. The prostate also contained small amounts of serine glycerophospholipids and sphingomyelin. The relative proportions of fatty acids in the different phospholipid classes were also determined. Arachidonic acid in prostatic phospholipids is contributed primarily by ethanolamine glycerophospholipids. This fraction contained 65-69 mol% plasmalogens, whereas choline and serine glycerophospholipid fractions contained less than 5 mol% plasmalogens. Ethanolamine, choline and serine plasmalogens contained mainly vinyl ethers of palmitic and stearic aldehydes. Ethanolamine plasmalogens also contained the vinyl ether of oleic aldehyde.     

Electrospray ionization mass spectrometry analyses of nuclear membrane phospholipid loss after reperfusion of ischemic myocardium

The role of nuclear membrane phospholipids as targets of phospholipases resulting in the generation of nuclear signaling messengers has received attention. In the present study, we have exploited the utility of electrospray ionization mass spectrometry to determine the phospholipid content of nuclei isolated from perfused hearts. Rat heart nuclei contained choline glycerophospholipids composed of palmitoyl and stearoyl residues at the sn-1 position with oleoyl, linoleoyl, and arachidonoyl residues at the sn-2 position. Diacyl molecular species were the predominant molecular subclass in the choline glycerophospholipids, with the balance of the molecular species being plasmalogens. In the ethanolamine glycerophospholipid pool from rat heart nuclei approximately 50% of the molecular species were plasmalogens, which were enriched with arachidonic acid at the sn-2 position. A 50% loss of myocytic nuclear choline and ethanolamine glycerophospholipids was observed in hearts rendered globally ischemic for 15 min followed by 90 min of reperfusion in comparisons with the content of these phospholipids in control perfused hearts. The loss of nuclear choline and ethanolamine glycerophospholipids during reperfusion of ischemic myocardium was partially reversed by the calcium-independent phospholipase A(2) (iPLA(2)) inhibitor bromoenol lactone (BEL), suggesting that the loss of nuclear phospholipids during ischemia/reperfusion is mediated, in part, by iPLA(2). Western blot analyses of isolated nuclei from ischemic hearts demonstrated that iPLA(2) is translocated to the nucleus after myocardial ischemia. Taken toghether, these studies have demonstrated that nuclear phospholipid mass decreases after myocardial ischemia by a mechanism that involves, at least in part, phospholipolysis mediated by iPLA2.     

Identification of plasmalogen as the major phospholipid constituent of cardiac sarcoplasmic reticulum

The phospholipid molecular species of canine myocardial sarcoplasmic reticulum were identified by fast atom bombardment mass spectrometry, reverse-phase high-performance liquid chromatography, and other conventional techniques. Cardiac sarcoplasmic reticulum contains 1.4 mumol of lipid Pi/mg of protein which is comprised of 53% plasmalogen. Cardiac sarcoplasmic reticulum ethanolamine glycerophospholipid contains 73% plasmalogen that is predominantly comprised of moieties with 18-carbon vinyl ethers at the sn-1 position and arachidonic acid at the sn-2 position. In contrast, canine skeletal muscle sarcoplasmic reticulum contains only 19% plasmalogen that is predominantly comprised of ethanolamine plasmalogen (78% of skeletal muscle sarcoplasmic reticulum ethanolamine glycerophospholipid) with arachidonic and docosatetraenoic acids at the sn-2 position. The possibility that tetraenoic ethanolamine plasmalogens in both cardiac and skeletal muscle sarcoplasmic reticulum facilitate calcium translocation by their propensity for adopting a hexagonal II conformation at physiologic temperatures is discussed.     

Fatty acid composition of choline and ethanolamine glycerophospholipid subclasses in heart tissue of mammals and migratory and demersal fish

The distribution and fatty acid composition of cardiac choline and ethanolamine glycerophospholipids in both migratory and demersal fish and bovine and pig were determined. Phospholipid contents (mg/g heart) were 4.7-9.4 in demersal fish, 14.0-16.5 in migratory fish, and 16.8-20.6 in mammals. Phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were the major components in the phospholipid fraction. Diacyl forms represented 50.2-88.1% of PC in all animals, while plasmalogens comprised 47.0% in bovine, 8.2% in pig and 6.2-7.2% in four species of fish. In PE, plasmalogens varied from 45.0% in bovine and 57.9% in pig to 26.1-29.7% in fish. This glycerophospholipid subclass was identified as containing higher proportions of polyunsaturated fatty acids (PUFAs; 20:4, 20:5, and 22:6) than found in alkylacyl- and diacyl-glycerophospholipids. Qualitative and quantitative differences were found in PE-plasmalogen between land mammals and fish, especially with regard to n-3 fatty acid composition, but no significant difference was noted between migratory and demersal fish.     

Differential turnover of polyunsaturated fatty acids in plasmalogen and diacyl glycerophospholipids of isolated cardiac myocytes

To investigate the relative turnover of esterified polyunsaturated fatty acids in diacylglycerophospholipids and plasmalogens in isolated cardiac myocytes, we characterized the phospholipid composition and distribution of radiolabel in different phospholipid classes and in individual molecular species of diradyl choline (CGP) and ethanolamine (EGP) glycerophospholipids after incubation of isolated cardiac myocytes with [3H]arachidonate or [14C]linoleate. Plasmalogens in CGP (55%) and EGP (42%) quantitatively accounted for the total plasmalogen content (39%) of cardiac myocyte phospholipids. Plasmalogens comprised 86% and 51% of total arachidonylated CGP and EGP mass, respectively, and [3H]arachidonate was primarily incorporated into plasmalogens in both CGP (65%) and EGP (61%) classes. The specificity activity of [3H]arachidonylated diacyl-CGP was approximately 2- to 5-fold greater than that of [3H]arachidonylated choline plasmalogen, whereas comparable specific activities were found in the [3H]arachidonate-labeled ethanolamine plasmalogen and diacyl-EGP pools. Of the total linoleate-containing CGP and EGP mass, 54% and 57%, respectively, was esterified to plasmalogen molecular species. However, [14C]linoleate was almost exclusively incorporated into diacyl-CGP (96%) and diacyl-EGP (86%). The specific activities of [14C]linoleate-labeled diacyl-CGP and diacyl-EGP were 5- to 20-fold greater than that of the [14C]linoleate-labeled plasmalogen pools. The differential incorporation of polyunsaturated fatty acids in plasmalogens and diacylglycerophospholipids demonstrates that the metabolism of the sn-2 fatty acyl moiety in these phospholipid subclasses is differentially regulated, possibly fulfilling separate and distinct physiologic roles.     

Separation of intact plasmalogens and all other phospholipids by a single run of high-performance liquid chromatography

Plasmalogens are a unique subclass of glycerophospholipids characterized by the presence of a vinyl ether bond at the sn-1 position of the glycerol backbone, and they are found in high concentration in cellular membranes of many mammalian tissues. However, separation of plasmalogens as intact phospholipids has not been reported. This article describes a high-performance liquid chromatographic method that can separate intact ethanolamine plasmalogens (pl-PEs) and choline plasmalogens (pl-PCs) as well as all other phospholipid classes usually found in mammalian tissues by a single chromatographic run. The separation was obtained using an HPLC diol column and a gradient of a hexane/isopropanol/water system containing 1% acetic acid and 0.08% triethylamine. The HPLC method allowed a clear separation of plasmalogens from their diacyl analogues. The HPLC method, as applied to the study of peroxidation in human erythrocytes by a hydroperoxide, demonstrated that pl-PEs were targeted twice as much as their diacyl analogues.     

Sterol carrier protein-2 expression alters phospholipid content and fatty acyl composition in L-cell fibroblasts

The effects sterol carrier protein-2 (SCP-2) expression on L-cell phospholipid levels and fatty acyl composition was assessed using L-cells transfected with the murine cDNA encoding for either the 15 kDa proSCP-2 or 13.2 kDa SCP-2. Expression of these proteins reduced total phospholipid mass (nmol/mg protein) by 24% and reduced the cholesterol to phospholipid ratio 60 and 28%, respectively. In 15 kDa proSCP-2 expressing cells, individual phospholipid class masses, excluding sphingomyelin (CerPCho), were reduced as follows: phosphatidylinositol (PtdIns) and phosphatidylserine (PtdSer) > ethanolamine glycerophospholipid (EtnGpl) > choline glycerophospholipid (ChoGpl). Furthermore, ethanolamine plasmalogen mass was decreased 25%, while choline plasmalogen mass was elevated 30% in 15 kDa proSCP-2 expressing cells. In 13.2 kDa SCP-2 expressing cells, phospholipid class mass was decreased as follows: PtdIns and PtdSer > ChoGpl. These changes in phospholipid mass resulted in altered cellular phospholipid composition. Expression of either protein differentially altered the type of fatty acid esterified onto the phospholipids. These effects included a greater proportion of polyunsaturated fatty acids and a reduction in saturated fatty acids, although 15 kDa proSCP-2 expression had a more robust effect on these parameters than did 13.2 kDa SCP-2 expression. In summary, expression of SCP-2 reduced individual phospholipid class mass, except for CerPCho, and altered the fatty acid composition of each phospholipid class examined.These results clearly demonstrate that SCP-2 expression altered basal phospholipid levels, suggesting that SCP-2 can alter the function of endoplasmic reticulum phospholipid synthetic enzymes.     

Synthesis and content of ether-linked glycerophospholipids in the harderian gland of rabbits.

Although harderian glands are rich in neutral glycerolipids with ether bonds, less than 20% of the choline glycerophospholipids have ether bonds in the white and pink portions of the adult rabbit harderian gland. Only 6% of these are plasmalogens while 94% are alkylacyl glycerophosphocholines. The ethanolamine glycerophospholipids include 37% with ether bonds in both white and pink portions. In the white portion 96% are plasmalogens but only 19% are plasmalogens in the pink portion. The microsomal ethanolaminephosphotransferase (EC 2.7.8.1) is more active with diacylglycerols than with alkylacylglycerols. The microsomal cholinephosphotransferase (EC 2.7.8.2) is equally active with both diradylglycerols. Particularly with microsomes from the pink portion, the apparent Km values for CDPethanolamine and CDPcholine are ower in the presence of alkylacylglycerols than in the presence of diacylglycerols. The incorporation of radioactivity from CDP[14C]ethanolamine and CDP[14C]choline into ethanolamine and choline plasmalogens was increased several-fold by addition of alkylacylglycerols but was not increased substantially by addition of diacylglycerols.     

Analysis of phospholipid species in rat peritoneal surface layer by liquid chromatography/electrospray ionization ion-trap mass spectrometry

The main phospholipids in rat peritoneal surface layer were analyzed by normal-phase high-performance liquid chromatography (HPLC) coupled with electrospray ionization (ESI) ion-trap mass spectrometry (MS). By using a silica gel column and a gradient of hexane/isopropanol/water as mobile phase containing 5 mmol/L ammonium formate as modifiers, a baseline separation of glycerophosphoehtanolamine (PE), phosphatidylinositol (PI), phosphatidylserine (PS), phosphatidylcholine (PC), sphingomyelin (SM) and lyso-phosphatidylcholine (LPC) was obtained and more than 90 phospholipid constituents in rat peritoneal surface were identified and determined by on-line ion-trap MS detection. The major ethanolamine glycerophospholipids in rat peritoneal surfaces were plasmalogens that were highly enriched in polyunsaturated fatty acids at the sn-2 position. In addition, the fragmentation patterns for each phospholipid class by the ion-trap MS were discussed.     

Lipid composition of purified transverse tubule membranes isolated from amphibian skeletal muscle

The level and proportion of lipids and their fatty acid composition were analyzed in highly purified transverse tubule membranes of amphibian skeletal muscle. Tubule membranes show (a) a higher content of lipids, (b) a higher phospholipid/cholesterol ratio and (c) a different phospholipid composition from other subcellular fractions, such as the light and heavy membranes from sarcoplasmic reticulum, which are similar in lipid profile. Transverse tubule membranes are characterized by a high percentage of phosphatidylserine and sphingomyelin and a low proportion of phosphatidylcholine compared with the other membranes. All three show a high proportion of ethanolamine plasmalogens (50% of the total ethanolamine glycerophospholipid). Transverse tubule membrane lipids contain a high proportion of 20- and 22-carbon polyunsaturated fatty acids, predominantly 20:4, 20:5, 22:5 and 22:6. Arachidonate predominates in phosphatidylinositol, eicosapentaenoate and docosahexaenoate in ethanolamine and serine glycerophospholipids.     

THE FATTY ACID COMPOSITION OF PHOSPHOLIPIDS AND GLYCOLIPIDS IN JIMPY MOUSE BRAIN

Abstract— Phospholipids and sphingolipids from brains of normal and Jimpy mice were isolated in a pure form by thin-layer chromatographic procedures. The fatty acid composition of the major phospholipids, i.e. ethanolamine glycerophospholipids, serine glycerophospholipids, choline glycerophospholipids and inositol glycerophospholipids, as well as sphingomyelin, cerebrosides and sulphatides was determined by gas-liquid chromatography. A specific fatty acid pattern for each of the four glycerophospholipids was found. The fatty acid composition of inositol glycerophospholipid, which has not previously been studied in mouse brain, was characterized by a high concentration of arachidonic acid. After 16 days of age, fatty acid analysis showed definite differences between the phospholipids from normal and mutant brains. A small increase of polyunsaturated fatty acids in glycerophospholipids of ethanolamine, serine and choline from the Jimpy central nervous system was found, which has been explained by the myelin deficiency. Sphingomyelin, cerebrosides and sulphatide analyses showed a wide distribution of saturated and mono-unsaturated fatty acids in both normal and mutant mice. A reduction in the amount of long-chain fatty acids was demonstrated in mutant brain sphingolipids; in sulphatides and cerebrosides, the amount of non-hydroxy fatty acids was reduced to a greater extent than in sphingomyelin. The distribution of fatty acids in sphingolipids from the myelin and microsomal fractions was also investigated in both types of mice. Cerebrosides were characterized by a high content of long-chain fatty acids in myelin as well as in microsomes. Sulphatides and sphingomyelin, on the other hand, showed a higher content of medium-chain fatty acids in microsomes than in myelin. In the mutant brain, the amount of long-chain fatty acids was reduced in both subcellular fractions. The deviation from normal in the pattern of fatty acid distribution in Jimpy brain is discussed in relation to the current concepts of glycolipid biosynthesis.     

Lipids from nerve tissues of the horseshoe crab, Limulus polyphemus.

1. The predominant lipids of nerve cords, ganglion and brain from horseshoe crabs were cholesterol (11% of lipid) and phospholipid (81% of lipid). 2. Major phospholipids were phosphatidyl ethanolamine and phosphatidyl choline with lesser amounts of phosphatidyl serine and phosphatidyl inositol and sphingomyelin. 3. The phospholipid fraction was characterized by a high content of plasmalogen, i.e. alk-1-enyl acyl phosphatides, so that 42% of the ethanolamine phosphatides were the plasmalogen, phosphatidal ethanolamine. 4. Phosphatidyl choline and phosphatidyl ethanolamine were high in polyunsaturation with 20:4 and 20:5 major fatty acids. Sphingomyelin had predominantly long chain saturated fatty acids. 5. Cerebrosides and gangliosides, which are associated with vertebrate nerve tissues, were absent from nerves of horseshoe crabs.     

Effects of Maturation on the Phospholipid and Phospholipid Fatty Acid Compositions in Primary Rat Cortical Astrocyte Cell Cultures

Phospholipid and phospholipid fatty acid compositional changes were studied in rat cortical astrocytes during dibutyryl cyclic adenosine monophosphate (dBcAMP, 0.25 mM) treatment starting after 14 days in culture (DIC). After 15 DIC, ethanolamine- and choline glycerophospholipid levels were increased 1.2- and 1.3-fold, respectively in treated compared to control cells. However, after 21 and 28 DIC, these levels were not significantly different between groups. Both groups had an increase in phosphatidylserine levels with increasing time in culture. Similarly, ethanolamine plasmalogen levels were transiently elevated after 21 DIC, but returned to previous levels after 28 DIC. The phospholipid fatty acid compositions for the acid stable and labile ethanolamine- and choline glycerophospholipids indicated that in dBcAMP treated cells, 20:4 n-6 and 22:6 n-3 proportions were elevated with increasing time in culture relative to control cells. As 20:4 n-6 proportions increased, there was a concomitant decrease in 20:3 n-9 proportions, suggesting an up regulation of n-6 series elongation and desaturation. In contrast, in control cells, the 20:4 n-6 proportions decreased with a corresponding increase in the 20:3 n-9 proportions. Thus, in treated cells, the cellular phospholipid fatty acid composition was dramatically different than control cells, suggesting that dBcAMP treatment may act to increase fatty acid elongation and desaturation.     

Diacyl,Alkylacyl, and Alkenylacyl Phospholipids of Meloidogyne javanica Females

The phospholipid composition and acyl, alkyl, and alkenyl group compositions of diacyl, alkylacyl, and alkenylacyl phosphoglycerides of M. javanica were investigated. Phospholipid was comprised of 61.7% choline phosphoglyceride, 22.0% ethanolamine phosphoglyceride, and smaller quantities of six other lipids. Phospholipid fatty acid was more unsaturated than neutral lipid fatty acid and contained 61.3% octadecenoic (18:1) acid. Fatty acid at the 1-position of diacyl phospholipids was shorter and more saturated than that at the 2-position. Compared to choline phosphoglyceride, ethanolantine phosphoglyceride contained less 18:1 and 20:5 and more 18:0 and 20:0 acid. Alkenylacyl and alkylacyl compounds comprised 34.6% and 9.3%, respectively, of the ethanolamine phosphoglyceride but only 0.5% and 0.6% of the choline phosphoglyceride. Alkenylacyl and alkylacyl ethanolamine phosphoglycerides contained a smaller percentage of 20-carbon polyunsaturated acid at their 2-positions than did their diacyl analogue. At least 95% of the alkenyl and alkyl groups were 18:0 compounds. Tomato roots did not contain alkenylacyl or alkylacyl phosphoglycerides; their occurrence in M. javanica is a significant biochemical difference between the nematode and its host.     

Posttranslational Regulation of Fatty Acyl-CoA Reductase 1, Far1, Controls Ether Glycerophospholipid Synthesis

Plasmalogens are a major subclass of ethanolamine and choline glycerophospholipids in which a long chain fatty alcohol is attached at the sn-1 position through a vinyl ether bond. This ether-linked alkyl bond is formed in peroxisomes by replacement of a fatty acyl chain in the intermediate 1-acyl-dihydroxyacetone phosphate with a fatty alcohol in a reaction catalyzed by alkyl dihydroxyacetone phosphate synthase. Here, we demonstrate that the enzyme fatty acyl-CoA reductase 1 (Far1) supplies the fatty alcohols used in the formation of ether-linked alkyl bonds. Far1 activity is elevated in plasmalogen-deficient cells, and conversely, the levels of this enzyme are restored to normal upon plasmalogen supplementation. Down-regulation of Far1 activity in response to plasmalogens is achieved by increasing the rate of degradation of peroxisomal Far1 protein. Supplementation of normal cells with ethanolamine and 1-O-hexadecylglycerol, which are intermediates in plasmalogen biosynthesis, accelerates degradation of Far1. Taken together, our results indicate that ether lipid biosynthesis in mammalian cells is regulated by a negative feedback mechanism that senses cellular plasmalogen levels and appropriately increases or decreases Far1.     

Lipid composition of human neural tumors.

Gangliosides, cholesterol, and phospholipids were quantitated in the tissues of 11 human neural tumors and the cells of two gliomas cultured in vitro. All tumor tissues contained higher water concentrations but lower total lipid concentrations than either human grey or white matter. In general they contained less cholesterol, sphingomyelin, and serine glycerophospholipid but more choline glycerophospholipid than white matter. Concentrations of total ganglioside sialic acid were intermediate between grey and white matter. Compared with normal brain, all tumors had greater proportions of the structurally less complex gangliosides and smaller proportions of the more complex gangliosides. This was most marked in the rapidly growing tumors while the better differentiated astrocytomas contained the greatest proportions of complex gangliosides. The cells of the cultured tumors contained amounts of total lipid and total phospholipid similar to their parent tissues. However, the cultures had less cholesterol, sphingomyelin, and total ganglioside than their parent tissues. There were significant amounts of choline and ethanolamine plasmalogens in both cultures and parent tissues. The ganglioside patterns of both cultures were complex but they contained a greater proportion of structurally simpler gangliosides than their parent tissues.-Yates, A. J., D. K. Thompson, C. P. Boesel, C. Albrightson, and R. W. Hart. Lipid composition of human neural tumors.     

Characterization of gastric mucosal membranes: lipid composition of purified gastric microsomes from pig, rabbit, and frog

The lipid compositions of the gradient-purified gastric microsomal membranes from the fundic mucosa of pig, rabbit, and frog were determined. The total lipid content varied widely. Compared to the rabbit (21.6 ± 0.6 mg/100 mg protein), the pig had about twice as much and the frog about three times as much lipid. The levels of cholesterol were higher in both mammalian species (about 32% of the lipid) compared to frog (23%). Phospholipids accounted for about 45, 54, and 52% of the total microsomal lipids from pig, rabbit, and frog and the molar ratios of cholesterol to phospholipid in the three species were 1.95, 1.6, and 1.17, respectively. Phosphatidyl choline and phosphatidyl ethanolamine together constituted about 75% of the total phospholipids in pig and frog and 93% in rabbit gastric microsomes. Sphingomyelin comprised 19.3, 3.2, and 1.5% in pig, rabbit, and frog, respectively. Phosphatidyl inositol constituted 5, 2.7, and 23.6% in pig, rabbit, and frog, respectively. The ratios of phosphatidyl ethanolamine to phosphatidyl choline were 1.17, 1.1, and 0.85 in pig, rabbit, and frog, respectively. The saturated fatty acids 16:0 and 18:0 and the unsaturated fatty acid 18:1 and 18:2 were the predominant fatty acids in all phospholipids. The ratios of saturated to unsaturated fatty acids were between 0.8 and 0.9 in phosphatidyl choline and 0.27 and 0.5 in phosphatidyl ethanolamine from all three species. The contributions by saturated fatty acids were much more in phosphatidyl inositol and sphingomyelin than in phosphatidyl choline and phosphatidyl ethanolamine from all species. Position 1 of phosphatidyl choline had 63% saturated and 37% unsaturated fatty acids; while the reverse was true for position 2. Phosphatidyl ethanolamine, however, had 85% saturated fatty acids in position 1 compared to only 25% in position 2. Arachidonic acid (20:4) was present in significant amounts in all species located exclusively at position 2 of both phosphatidyl choline and phosphatidyl ethanolamine.     

The effect of temperature-and oxygen-acclimation on phospholipids of goldfish (Carassius auratus L.) brain mitochondria

Goldfish (Carassius auratus L.) were temperature- and oxygen-acclimated and the composition of the phospholipids and their acyl groups in brain mitochondria was determined. The proportion of ethanolamine to choline phospholipid was greater while the plasmenyl ethanolamine value (P-GPE/D- + P-GPE) was lower at the low acclimation temperature. For the ethanolamine glycerophospholipids, a rise in the ratio n-6/n-3 fatty acyl groups occurred with cold acclimation. No significant change in the ratio was exhibited by phosphatidyl choline. When the oxygen level was increased, at either acclimation temperature, a rise in the GPE/GPC ratio and the plasmenyl ethanolamine value resulted. The n-6/n-3 ratio was generally increased for the ethanolamine classes when the oxygen concentration was raised. The possible significance of these changes is discussed.     

Composition and incorporation of [3H]arachidonic acid into molecular species of phospholipid classes by cultured human endothelial cells

Based on quantitative high-performance liquid chromatographic analyses of molecular species in selected phospholipid subclasses from culture human umbilical vein endothelial cells, the relative degree of unsaturation was ethanolamine plasmalogens greater than phosphatidylethanolamine greater than phosphatidylcholine. A total of 36 different molecular species were identified in the phosphatidylcholine fraction. Interestingly, the phosphatidylcholine contained a significant amount (11.7%) of the dipalmitoyl species, a lipid normally associated with lung surfactant. The arachidonoyl-containing molecular species of phosphatidylserine/inositol were labeled to the highest extent and the ethanolamine plasmalogens contained the lowest specific radioactivity after incubating [3H]arachidonic acid with human endothelial cells for 4 h. Within each phospholipid subclass the arachidonoyl species where both acyl groups of the phospholipid are unsaturated (20:4-20:4, 18:2-20:4 + 16:1-20:4, and 18:1-20:4) had higher specific radioactivities, after labeling with [3H]arachidonic acid, than those that contained saturated aliphatic chains (16:0-20:4 and 18:0-20:4). This indicates that the unsaturated species have higher turnover rates.     

Preferential formation of the hydroperoxide of linoleic acid in choline glycerophospholipids in human erythrocytes membrane during peroxidation with an azo initiator

The formation of phospholipid hydroperoxides was monitored in human red blood cell (RBC) membranes that had been peroxidized with an azo initiator. Peroxidation of RBC membranes caused a profound decrease in the amount of polyunsaturated fatty acids and concomitantly hydroperoxides, as primary products of peroxidation, appeared in the phospholipids. Hydroperoxides were predominantly generated in choline glycerophospholipid (CGP), while the extent of formation of ethanolamine glycerophospholipid (EGP) hydroperoxides was low and their presence was transient. Hydroxy and hydroperoxy moieties in CGP were identified as 9-hydroxy and 13-hydroxy octadecanoic acid, derived from linoleic acid, by gas chromatography-mass spectrometric analysis. No consistent generation of hydroperoxide from arachidonic acid was evident in CGP. The CGP-hydroperoxide accounted for approximately 76% of linoleic acid consumed during peroxidation of RBC membranes. The prominent generation of phospholipid hydroperoxides was observed in the linoleic acid-rich membranes from rabbit RBC, indicating that the level of linoleic acid in phospholipids determins, in part, the extent of formation of phospholipid hydroperoxides. Aldehydic phospholipids, as secondary products of peroxidation, were detected in oxidized membranes. EGP was the most prominent aldehydic phospholipid, while negligible amounts of aldehydic CGP were formed. This study indicates that the process of oxidation of individual phospholipids clearly differs among phospholipids and depends on the structure of each.