Identification of Two Molecular Species of Rat Brain Phosphatidylcholine that Rapidly Incorporate and Turn Over Arachidonic Acid In Vivo

Abstract: In vivo rates of arachidonic acid incorporation and turnover were determined for molecular species of rat brain phosphatidylcholine (PtdCho) and phosphatidylinositol (PtdIns). [³H]Arachidonic acid was infused intravenously in pentobarbital-anesthetized rats at a programmed rate to maintain constant plasma specific activity for 2–10 min. At the end of infusion, animals were killed by microwave irradiation, and brain phospholipids were isolated, converted to diacylglycerobenzoates, and resolved as molecular species by reversed-phase HPLC. Most [³H]arachidonate (>87%) was incorporated into PtdCho and PtdIns, with arachidonic acid at the sn -2 position and with oleic acid (18:1), palmitic acid (16:0), or stearic acid (18:0) at the sn -1 position. However, 10–15% of labeled brain PtdCho eluted in a small peak containing two molecular species with arachidonic acid at the sn -2 position and palmitoleic acid (16:1) or linoleic acid (18:2) at the sn -1 position. Analysis demonstrated that tracer was present in both the 16:1–20:4 and 18:2–20:4 PtdCho species at specific activities 10–40 times that of the other phospholipids. Based on the measured mass of arachidonate in each phospholipid molecular species, half-lives were calculated for arachidonate of <10 min in 16:1–20:4 and 18:2–20:4 PtdCho and 1–3 h in 16:0–20:4, 18:0–20:4, and 18:1–20:4 PtdCho and PtdIns. The very short half-lives for arachidonate in the 16:1–20:4 and 18:2–20:4 PtdCho molecular species suggest important roles for these molecules in brain phospholipid metabolism and signal transduction.     

Properties of the binding sites for the sn-1 and sn-2 acyl chains on the phosphatidylinositol transfer protein from bovine brain

We have studied the properties of the fatty acyl binding sites of the phosphatidylinositol transfer protein (PI-TP) from bovine brain, by measuring the binding and transfer of pyrenylacyl-containing phosphatidylinositol (PyrPI) species and pyrenylacyl-containing phosphatidylcholine (PyrPC) species as a function of the acyl chain length. The PyrPI species carried a pyrene-labeled acyl chain of variable length in the sn-2 position and either palmitic acid [C(16)], palmitoleic acid [C(16:1)], or stearic acid [C(18:1)] in the sn-1 position. Binding and transfer of the PI species increased in the order C(18) less than C(16) less than C(16:1), with a distinct preference for those species that carry a pyrenyloctanoyl [Pyr(8)] or a pyrenyldecanoyl [Pyr(10)] chain. The PyrPC species studied consisted of two sets of positional isomers: one set contained a pyrenylacyl chain of variable length and a C(16) chain, and the other set contained an unlabeled chain of variable length and a Pyr(10) chain. The binding and transfer experiments showed that PI-TP discriminates between positional isomers with a preference for the species with a pyrenylacyl chain in the sn-1 position. This discrimination is interpreted to indicate that separate binding sites exist for the sn-1 and sn-2 acyl chains. From the binding and transfer profiles it is apparent that the binding sites differ in their preference for a particular acyl chain length. The binding and transfer vs chain length profiles were quite similar for C(16)Pyr(x)PC and C(16)Pyr(x)PI species, suggesting that the sn-2 acyl chains of PI and PC share a common binding site in PI-TP.     

银杏叶片磷脂酰甘油脂肪酸分子种组成及其位置分布

用高效液相色谱法和酶解的方法检测了银杏叶片磷脂酰甘油(PG)脂肪酸的分子种组成和位置分布,确定银杏叶片PG主要分子种的脂肪酸组成(sn-1/sn-2)是18:3／16:1(3t),18:3／16:0,18:2／16:1(3t),18:2／16:0,18:1／16:1(3t),16:0／16:1(3t),18:1／18:1,18:/16：0和16:0和16:0／16:0。银杏叶片PC脂肪酸组成和位置分布的分析结果表明,C18脂肪酸主要位于sn-l位,16:1(3t)只分布于sn-2位,16:0在sn-1位和sn-2位上均有发现。sn-1位上的不饱和度∑u大于sn-2位上的∑u。     

Regiospecific distribution of fatty acids in triacylglycerols of Artemia franciscana nauplii enriched with fatty acid ethyl esters

This paper reports the positional distribution of fatty acids in triacylglycerols (TAG) of Artemia franciscana nauplii enriched with each of palmitic (16:0), oleic (18:1n-9), linoleic (18:2n-6), linolenic (18:3n-3), eicosapentaenoic (20:5n-3), and docosahexaenoic (22:6n-3) acid ethyl esters. TAG extracted from the enriched and unenriched nauplii were subjected to regiospecific analysis to determine the fatty acid compositions of the sn-1(3) and sn-2 positions of TAG. In the unenriched nauplii, 16:0, 18:1n-9, and 18:2n-6 were preferentially located in the sn-1(3) position followed by the sn-2 position [i.e. sn-1(3)>sn-2], whereas 18:3n-3 was concentrated in the sn-2 position [i.e. sn-2>sn-1(3)]. Contents of 20:5n-3 and 22:6n-3 were low. After the nauplii were enriched with each of the ethyl esters for 18 h, fatty acid fed to the nauplii showed higher content in the sn-1(3) position than in the sn-2 position [i.e. sn-1(3)>sn-2]. Distribution pattern of 18:3n-3 changed from sn-2>sn-1(3) to sn-1(3)>sn-2 during the enrichment with 18:3n-3 ethyl ester. Increases in all of the fatty acids in TAG were attributed to that in the sn-1(3) position much more than that in the sn-2 position. Artemia nauplii appear to be characterized by preferential incorporation of exogenous fatty acids into the sn-1(3) position of TAG, even though endogenous fatty acids are esterified in the opposite position.     

Changes of membrane phospholipid composition of human erythrocytes in hyperlipidemias. II. Increases in distinct molecular species of phosphatidylethanolamine and phosphatidylcholine containing arachidonic acid.

The molecular species composition of red blood cell diacyl-phosphatidylcholine (PC), diacyl-phosphatidylethanolamine (PE) and alkenylacyl-PE (plasmalogen PE) has been analyzed in normolipidemic and hyperlipidemic donors. In all three phospholipid subclasses the percentages of the species 16:0/20:4 were increased in hyperlipidemic patients. In diacyl-PE, 18:1/20:4 was also elevated. No changes were observed in the other quantitatively important molecular species containing arachidonic acid at sn-2, namely 18:0/20:4. The rise in 16:0/20:4 in diacyl-PC and diacyl-PE of hyperlipidemic donors was accompanied by a fall in molecular species with linoleic acid (18:2) at sn-2 (in particular 18:1/18:2). In alkenylacyl-PE the elevation of 16:0/20:4 was compensated by a decrease in species with docosatetraenoic acid (22:4) at sn-2 in particular by a fall in 16:0/22:4. Among all donors, the percentages of 16:0/20:4 in diacyl-PC and PE were positively associated with plasma total cholesterol levels. The changes in molecular species composition of PC and PE in hyperlipidemia are expected to alter the function of erythrocyte membrane transport proteins and--if present also in other cell types--to affect eicosanoid metabolism.     

Lysophosphatidic acid (LPA) receptors of the EDG family are differentially activated by LPA species. Structure-activity relationship of cloned LPA receptors

We examined the structure-activity relationship of cloned lysophosphatidic acid (LPA) receptors (endothelial cell differentiation gene (EDG) 2, EDG4, and EDG7) by measuring [Ca(2+)](i) in Sf9 insect cells expressing each receptor using LPA with various acyl chains bound at either the sn-1 or the sn-2 position of the glycerol backbone. For EDG7 the highest reactivity was observed with LPA with Delta9-unsaturated fatty acid (oleic (18:1), linoleic (18:2), and linolenic (18:3)) at sn-2 followed by 2-palmitoleoyl (16:1) and 2-arachidonoyl (20:4) LPA. In contrast, EDG2 and EDG4 showed broad ligand specificities, although EDG2 and EDG4 discriminated between 14:0 (myristoyl) and 16:0 (palmitoyl), and 12:0 (lauroyl) and 14:0 LPAs, respectively. EDG7 recognizes the cis double bond at the Delta9 position of octadecanoyl residues, since 2-elaidoyl (18:1, trans) and 2-petroselinoyl (18:1, cis-Delta12) LPA were poor ligands for EDG7. In conclusion, the present study demonstrates that each LPA receptor can be activated differentially by the LPA species.     

Studies on Composition of Molecular Species of Phosphatidylglycerol in Relation to Cold-resistance of Poplar

The composition of molecular species and the positional distribution in fatty acids of phosphatidylglycerol (PG) isolated from poplar ( Populus deltoides cv. Lux 1-69/55 and Poeuramericarla cv.I- 45/51 ) leaves were analyzed by high-performance liquid chromatography (HPLC), enzym hydrolysis and gas phase chromatography (C,C), and the different cold-resistant poplars were compared with respect to the compositions of molecular species of PG isolated from their leaves. The results showed that the fatty acid compositions ( sn- 1/sn-2) of the major molecular species in PCs from poplar leaves were as follows: 18:3/18:2(18:2/18:3), 18:3/16: 1(3t); 18:3/16:0; 18:2/ 16:1 (3t); 16:0/18:2,18:2/16:0; 18: 1/16: l(3t); 16:0/16: l(3t); 18: 1/18: 1,16:0/18: 1( 18: 1/16:0); 16:0/16:0o The positional distribution of fatty acids in lPG from poplar leaves was found that 16:1(30 was exclusively occupied the sn-2 position, whereas 16:0 was present in both the sn1 position and the sn-2 position. The C18 acids were principally localized at the sn-2 position. The relative contents of the unsaturated molecular species of leaf PCs were more than 70% in both coldresistant poplar and cold-sensitive poplar. The ratio of the unsaturated/saturated molecular species of PG isolated from the cold-resistant Ⅰ -45 poplar was 3.10, which was higher than that of the PG from the cold-sensitive cottonwood, which was 2.38. The sum of the relative contents of the disaturated molecular species of the PG from poplar leaves was closely associated with the cold-resistance of plants. The ∑[ 16:0/16:0+ 16:0/16: l(3t) ] of the PG from cottonwood was higher than that of the PG from cold-resistant I -45 poplar. The differences in the compositions of molecular species and the phase transition temperatures of PCs between cold-resistant and cold-sensitive plants were discussed in terms of the pathways and the activities of selective acyhransferases involved in the PG biosynthesis in chloroplast.     

The effect of sn-2 fatty acid substitution on phospholipase C enzyme activities.

The human monocyte cell line U937 expresses phospholipase A2 and phospholipase C activities and produces eicosanoids. The phospholipase C (PLC) activity exhibits substrate preference for phosphatidyl-choline (PC), rather than phosphatidylinositol or phosphatidylethanolamine. In order to characterize the PLC activity found in these cells, the effects of substitution of the sn-2 fatty acid on this activity were examined. PC substrates with palmitic acid (PC-2P), oleic acid (PC-2O), arachidonic acid (PC-2A) and linoleic acid (PC-2L) at the sn-2 position were used. The sn-1 fatty acid was palmitic acid. PC-2L and PC-2A with the longer-chain less-saturated fatty acids linoleic acid and arachidonic acid esterified at sn-2 were found to be better substrates for PLC activity than PC-2P or PC-2O in these cells. This preference was maintained even when substrate phospholipid was solubilized in non-ionic, anionic, cationic and zwitterionic amphiphiles. Furthermore, when a 500-fold excess of 1,2-diolein or 1,2-dipalmitin was added to the reaction, the specificity of the PLC activity for PC-2A and PC-2L remained unchanged. When similar experiments were performed with phosphatidylinositol as a substrate, we did not observe any effect when the sn-2 position was altered. These data show that the fatty acid constituent at the sn-2 position affects the observed PLC activity when phosphatidylcholine, but not phosphatidylinositol, is used as a substrate by these cells.     

Selective changes of docosahexaenoic acid-containing phospholipid molecular species in monkey testis during puberty

Puberty has a profound effect upon the biochemical composition of the testis. We previously demonstrated that puberty was accompanied by great increases in the content of docosahexaenoic acid (DHA; 22:6 n-3) and dihomogamma-linoleic acid (20:3 n-6) and decreases in arachidonic acid (AA; 20:4 n-6) in the phospholipids of testis. In this report, we analyze the composition of the phospholipid molecular species of the ethanolamine and choline glycerophospholipids in the testis of prepubertal (2 years old) and young adult (7-8 years old) monkeys, There was an increase in the DHA species and a decrease in arachidonic species. Interestingly, with few exceptions, among the three molecules with DHA or AA at the sn-2 position, only 16:0-22:6 and 18:0-20:4 changed selectively in opposite directions for both ethanolamine and choline glycerophospholipids. In contrast, there was no such selectivity seen in molecular species containing dihomogamma-linoleic acid or linoleic acid at the sn-2 position. All three dihomogamma-linoleic acid species increased and all three linoleic acid species decreased during puberty. In summary, at puberty, i.e., the onset of spermatogenesis, there are selective changes in the phospholipid molecular species, particularly those containing DHA and AA. These changes suggest a specific functional role of DHA-containing molecular species in the lipid bilayer membranes of sperm cells. A possible link between the composition of DHA-phospholipid molecular species and cellular function is discussed.     

Phosphatidyl choline fatty acid remodeling in the hepatic cell nuclei

This study was performed to determine whether fatty acids incorporated into liver cell nuclei phosphatidylcholine (PtdCho) could be remodeled in the isolated nuclear. For this reason, rat liver cell nuclei were incubated in vitro with [1-14C]20:4n-6-CoA. PtdCho molecular species with the highest specific activity had an unsaturated fatty acid at sn-1 and sn-2 positions (20:4-20:4>18:2-20:4>18:1-20:4). 16:0-20:4 and 18:0-20:4 PtdChos showed a minor specific activity. When labeled nuclei were reincubated in the absence of labeled substrate with the addition of cytosol, ATP and CoA, the specific activity of 20:4-20:4, 18:2-20:4 and 18:1-20:4 species decreased, while that of 16:0-20:4 and 18:0-20:4 increased. In conclusion, the asymmetric fatty acid distribution of saturated fatty acids at sn-1 position, and unsaturated fatty acids at sn-2 position of nuclear PtdCho molecular species was re-established by an acyl-CoA-dependent remodeling process.     

Molecular Species of Diacylglycerols and Phosphoglycerides and the Postmortem Changes in the Molecular Species of Diacylglycerols in Rat Brains

The molecular species of 1,2-diacyl-sn-glycerol (DAG), phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylinositol (PI), phosphatidylinositol 4-phosphate (PIP), and phosphatidylinositol 4,5-bisphosphate (PIP2) from brains of adult rats (weighing 150 g) were determined. The DAG, isolated from brain lipid extracts by TLC, was benzoylated, and the molecular species of the purified benzoylated derivatives were separated from each other by reverse-phase HPLC. The total amount and the concentration of each species were quantified by using 1,2-distearoyl-sn-glycerol (18:0-18:0) as an internal standard. About 30 different molecular species containing different fatty acids at the sn-1 and sn-2 positions of DAG were identified in rat brains (1 min postmortem), and the predominant ones were 18:0-20:4 (35%), 16:0-18:1 (15%), 16:0-16:0 (9%), and 16:0-20:4 (8%). The molecular species of PC, PE, PS, and PI were determined by hydrolyzing the lipids with phospholipase C to DAG, which was then benzoylated and subjected to reverse-phase HPLC. PIP and PIP2 were first dephosphorylated to PI with alkaline phosphatase before hydrolysis by phospholipase C. The molecular species composition of phosphoinositides showed predominantly the 18:0-20:4 species (50% in PI and approximately 65% in PIP and PIP2). PS contained mainly the 18:0-22:6 (42%) and 18:0-18:1 (24%) species. PE was mainly composed of the 18:0-20:4 (22%), 18:0-22:6 (18%), 16:0-18:1 (15%), and 18:0-18:1 (15%) species. In PC the main molecular species were 16:0-18:1 (36%), 16:0-16:0 (19%), and 18:0-18:1 (14%). Studies on postmortem brains (30 s to 30 min) showed a rapid increase in the total amount (from 40-50 nmol/g in 0 min to 210-290 nmol/g in 30 min) and in all the molecular species of DAG. Comparatively larger increases (seven- to 10-fold) were found for the 18:0-20:4 and 16:0-20:4 species. Comparison of DAG species with the molecular species of different glycerolipids indicated that the rapid postmortem increase in content of DAG was mainly due to the breakdown of phosphoinositides. However, a slow but continuous breakdown of PC to DAG was also observed.     

Remodelling of membrane phospholipids during transition to diapause and cold-acclimation in the larvae of Chymomyza costata (Drosophilidae)

The composition of molecular species of phosphatidylethanolamines (PEs) and phosphatidylcholines (PCs) was analysed in fat body and muscle tissues of Chymomyza costata larvae of different physiological states that markedly differed in their level of freeze-tolerance. Actively moving and feeding 3rd instar larvae had low (zero) capacity of freeze-tolerance and similar phospholipid (PL) compositions irrespective of their developmental destiny (non-diapause vs. diapause). Extensive remodelling of PL composition was found in these larvae in response to: (a) chilling of non-diapause larvae at 5 degrees C for 1 month; (b) developmental transition to diapause; and (c) chilling of diapause larvae. Transition to diapause and chilling led to an increase in freeze-tolerance. The increase in molar proportion of molecular species containing palmitic/linoleic (16:0/18:2) fatty acyls (FAs) esterified to sn-1/sn-2 positions of glycerol was the most prominent change, which was tightly statistically correlated with increasing freeze-tolerance. The increase of PLs with combination of 16:0/18:2 FAs was registered consistently in PEs and PCs in fat body and muscle tissues in response to chilling and to diapause onset. This increase was countered by a decreases of various molecular species, depending on tissue and lipid class. Most decreasing species shared one common theme: they had a saturated FA (palmityl, margaryl, stearyl) esterified at sn-1 position and a monounsaturate (palmitoleyl, oleyl) esterified at sn-2 position of glycerol. Possible adaptive meaning of PL molecular species remodelling is discussed.     

2H nuclear magnetic resonance order parameter profiles suggest a change of molecular shape for phosphatidylcholines containing a polyunsaturated acyl chain.

Solid-state 2H nuclear magnetic resonance spectroscopy was used to determine the orientational order parameter profiles for a series of phosphatidylcholines with perdeuterated stearic acid, 18:0d35, in position sn-1 and 18:1 omega 9, 18:2 omega 6, 18:3 omega 3, 20:4 omega 6, 20:5 omega 3, or 22:6 omega 3 in position sn-2. The main phase transition temperatures were derived from a first moment analysis, and order parameter profiles of sn-1 chains were calculated from dePaked nuclear magnetic resonance powder patterns. Comparison of the profiles at 37 degrees C showed that unsaturation causes an inhomogenous disordering along the sn-1 chain. Increasing sn-2 chain unsaturation from one to six double bonds resulted in a 1.6-kHz decrease in quadrupolar splittings of the sn-1 chain in the upper half of the chain (or plateau region) and maximum splitting difference of 4.4 kHz at methylene carbon 14. The change in chain order corresponds to a decrease in the 18:0 chain length of 0.4 +/- 0.2 A with 18:2 omega 6 versus 18:1 omega 9 in position sn-2. Fatty acids containing three or more double bonds in sn-2 showed a decrease in sn-1 chain length of 0.7 +/- 0.2 A compared with 18:1 omega 9. The chain length of all lipids decreased with increasing temperature. Highly unsaturated phosphatidylcholines (three or more double bonds in sn-2) had shorter sn-1 chains, but the chain length was somewhat less sensitive to temperature.(ABSTRACT TRUNCATED AT 250 WORDS)     

Acyl chain-based molecular selectivity for HL60 cellular phosphatidylinositol and of phosphatidylcholine by phosphatidylinositol transfer protein alpha

Mammalian phosphatidylinositol transfer protein alpha (PITP) is an intracellular lipid transporter with a binding site that can accommodate a single molecule of phosphatidylinositol (PI) or phosphatidylcholine (PC). Phospholipids are a heterogeneous population of molecular species that can be distinguished by their characteristic headgroups as well as their acyl chains at the sn-1 and sn-2 position. In this study, we have defined the acyl chain preference for PITPalpha when presented with a total population of cellular lipids. Recombinant PITPalpha loaded with bacterial lipid, phosphatidylglycerol (PG), was incubated with permeabilised HL60 cells, followed by recovery of PITPalpha by affinity chromatography. Lipids extracted from the PITPalpha were analysed by tandem electrospray ionisation mass spectrometry (ESI-MS) and showed total exchange of acquired bacterial lipids for HL60 cellular PI and PC. Detailed comparison of the molecular species composition of bound phospholipids with those in whole cells permitted the assessment of selectivity of acyl chain binding. For both phospholipid classes, progressive fractional enrichments in bound species possessing shorter acyl chains were apparent with a preference order: 16:1>16:0>18:1>18:0>20:4. A recapitulation of this specificity order was also seen from a dramatically altered range of molecular species present in HL60 cells enriched with arachidonate over many weeks of culture. We speculate that short-chain, saturate-binding preferences under both conditions may reflect properties in vivo. This is consistent with target cell membranes actively remodelling newly delivered phospholipids after transport rather than relying on the transport of the specific molecular species conventionally found in mammalian membranes.     

Incorporation and distribution of epoxyeicosatrienoic acids into cellular phospholipids.

The different regioisomers of epoxyeicosatrienoic acids derived from cytochrome P-450 monooxygenase are readily esterified into phospholipids of mastocytoma cells. Incorporation of 14,15-epoxyeicosatrienoic acid was concentration-dependent, with Km = 1.1 microM and Vmax = 36 pmol/min/10(7) cells. Half-maximal incorporation occurred in 30 min, reaching a steady-state concentration of 470 pmol/10(6) cells. This was slightly lower than the values for arachidonic acid (665 pmol/10(6) cells) or 5-hydroxyeicosatetraenoic acid (554 pmol/10(6) cells). The distribution of 14,15-epoxyeicosatrienoic acid was preferential in the order phosphatidylethanolamine greater than phosphatidylcholine greater than phosphatidylinositol greater than phosphatidyl serine much greater than neutral lipids plus fatty acids. This contrasted with 5(S)-hydroxyeicosatetraenoic acid, which was distributed primarily into phosphatidylcholine. Fast atom bombardment/tandem mass spectrometry facilitated identification of molecular species containing epoxyeicosatrienoic acids without relying on radioisotopes. Phosphatidylethanolamine plasmalogens with 16:1 or 18:2 at the sn-1 position, or an 18:0 acyl group, and phosphatidylcholine with 16:0 alkyl ether or an acyl group at the sn-1 position incorporated all possible epoxyeicosatrienoic acid regioisomers. Under basal conditions, cells eliminated 14,15-cis-epoxyeicosatrienoic acid slowly with a half-life of 34.9 +/- 7 h. Cells stimulated with calcium ionophore A23187 eliminated 14,15-epoxyeicosatrienoic acid rapidly. It was notable that its rate of release from phosphatidylcholine and phosphatidylinositol exceeded that for arachidonic acid. A coenzyme A-independent transacylase also catalyzed the transfer of epoxyeicosatrienoic acids from mastocytoma cell membranes into 1-palmitoyl-2-lysophosphatidylcholine. The cellular incorporation, release, and distribution of epoxyeicosatrienoic acids is distinctive and contrasts with most other eicosanoids, suggesting that these compounds may have both autocoid and nonautocoid functions.     

Mitochondrial lipids in Bufo arenarum full-grown oocytes

Both the content and composition of polar and neutral lipids from the mitochondrial fraction of ovarian full-grown Bufo arenarum oocytes were analysed in the present study. Triacylglycerols (TAG) represent 33% of the total lipids, followed by phosphatidylcholine (PC), free fatty acids (FFA) and phosphatidylethanolamine (PE). Diphosphatidylglycerol (DPG) or cardiolipin, a specific component of the inner mitochondrial membrane, represents about 4% of the total lipid content. Palmitic (16:0) and arachidonic (20:4n6) acids are the most abundant fatty acids in PC and PE, respectively. DPG is enriched in fatty acids with carbon chain lengths of 18, the principal component being linoleic acid. In phosphatidylinositol (PI), 20:4n6 and stearic acid (18:0) represent about 72 mol% of the total acyl group level. The main fatty acids in TAG are linoleic (18:2), oleic (18:1), and palmitic acids. The fatty acid composition of FFA and diacylglycerols (DAG) is similar, 16:0 being the most abundant acyl group. PE is the most unsaturated lipid and sphingomyelin (SM) has the lowest unsaturation index.     

Effect of unsaturation on the chain order of phosphatidylcholines in a dioleoylphosphatidylethanolamine matrix.

The properties of phosphatidylcholines (PCs) having a perdeuterated stearic acid, 18:0d35, in the sn-1 position and the fatty acid 18:0, 18:1 omega 9, 18:2 omega 6, 18:3 omega 3, 20:4 omega 6, 20:5 omega 3, or 22:6 omega 3 at the sn-2 position were investigated in a matrix of dioleoylphosphatidylethanolamine (DOPE) by 2H and 31P NMR spectroscopy. At a mole ratio of DOPE/PC = 5:1, the lipids form liquid crystalline lamellar phases below 40 degrees C and coexisting lamellar, inverse hexagonal (Hll), and cubic phases at higher temperatures. The sn-1 chain of the PCs in a DOPE matrix is appreciably more ordered than in pure PCs, corresponding to an increase in the hydrophobic bilayer thickness of approximately 1 A. Distearoylphosphatidylcholine in the DOPE matrix has a higher sn-1 chain order than the unsaturated PCs. We observed distinct differences in the lipid order of upper and lower sections of the hydrocarbon chains caused by changes of temperature, unsaturation, headgroups, and ethanol. Unsaturation lowers chain order, mostly in the lower third of the hydrocarbon chains. By contrast, the increase in chain order caused by the DOPE matrix and the decrease in order with increasing temperature have a constant magnitude for the upper two-thirds of the chain and are smaller for the lower third. Addition of 2 M ethanol reduced order parameters, in effect reversing the increase in chain order caused by the DOPE matrix.     

Selective changes to phosphatidylcholine and phosphatidylethanolamine molecular species in the developing fetal guinea pig liver and plasma

The molecular species composition of membrane phospholipids influences the activities of integral proteins and cell signalling pathways. We determined the effect of increasing gestational age on fetal guinea pig liver phosphatidylcholine (PC) and phosphatidylethanolamine (PE), and plasma PC molecular species composition. The livers were collected from fetuses (n = 5/time point) at 5 day intervals between 40 and 65 days of gestation, and at term (68 days). Hepatic PC and PE molecular species composition was determined by electrospray ionisation mass spectrometry. An increasing gestational age was accompanied by selective changes in individual molecular species. The proportion of the sn-1 18:0 species increased relative to the sn-1 16:0 species in liver PC, but not PE, with an increasing gestational age. 1-O-alkyl-2-acyl PC species concentrations decreased significantly between 40 and 45 days of gestation (40%), and 65 and 68 days (54%). Total 1-O-alkenyl-2-acyl PE species concentration increased between days 60 and 65, due to a rise in 1-O-16:0 alkyl/20:4 content, and then decreased until term. Between day 40 and term, PC and PE sn-2 18:2n-6 species concentrations increased 3-fold. PC16:0/18:2 increased gradually throughout gestation, while PC18:0/18:2 content only increased after day 65. The overall increase in PE18:2n-6 content was due to PE18:0/18:2 alone. The composition of plasma PC essentially reflected hepatic PC. Overall, these data suggest differential regulation of hepatic PC and PE molecular species composition during development which is essentially independent of the maternal fatty acid supply.     

Changes in the composition of membrane lipids in relation to differentiation in Aegle marmelos callus cultures

Changes in fatty acid, phospholipid and galactolipid contents during cellular and organ differentiation in Aegle marmelos have been described. Decrease in phosphatidylinositol content and presence of 3-trans-hexadecenoic acid in phosphatidylglycerol were related to greening and shoot buds differentiation. The galactolipids level, the monogalactosyl diglyceride/digalactosyl diglyceride ratio and the linolenic acid level (mainly in monogalactosyl diglyceride) increased with the degree of differentiation, indicating the possible biogenesis of functional chloroplasts.Abbreviations 2,4-D 2,4 dichlorophenoxyacetic acid - BA benzylaminopurine - DW dry weight - FW fresh weight - PC phosphatidylcholine - PE phosphatidylethanolamine - PI phosphatidylinositol - PG phosphatidylglycerol - PS phosphatidyl serine - MGDG monogalactosyl diglyceride - DGDG digalactosyl diglyceride - 16:0 palmatic acid - 18:0 stearic acid - 18:1 oleic acid - 18:2 linoleic acid - 18:3 linolenic acid - trans-16:1 3-trans-hexadecenoic acid     

Biosynthesis of diacylglycerols by rat intestinal mucosa in vivo.

The biosynthesis of diacylglycerols was studied in rat intestinal mucosa during in vivo absorption of a low molecular weight fraction fraction of butter oil and of the corresponding medium and long chain fatty acids. The experimental fat solutions were given by stomach tube to the animals after a 24-h fast and mucosal scraping were collected 3 h later. The lipids were isolated and the acylclycerols determined by combined thin-layer chromatography gas-liquid chromatography techniques and stereospecific analyses. Free fatty acid feeding led mainly to sn-1,2-diacyl-glycerols, which contained exogenous and endogenous fatty acids. During triacylglycerol feeding, both sn-1,2-and sn-2,3-diacylglycerols were recovered in significant amounts from the intestinal mucosa. The composition of the sn-2,3-diacylglycerols corresponded to that with exogenous fatty acids but the sn-1,2-diacylglycerols clearly contained both exogenous and endogenous fatty acids. In all cases it was possible to isolate endogenous sn-1,2-diacylglycerols made up largely of species with linoleic and arachidonic acids in the 2 position and palmitic and stearic acids in the 1 position, which apparently were not converted to triacylglycerols. The in vivo reacylation of 2-monoacylglycerols via both sn-1,2- and sn-2,3-diacylglycerols is in agreement with similar findings in vitro with everted sacs of rat intestinal mucosa.