Chlorinated fatty acid distribution in Mycobacterium convolutum phospholipids after growth on 1-chlorohexadecane.

The composition of phospholipids from Mycobacterium convolutum R22 was determined after growth at two temperatures (20 and 30 degrees C) with 1-chlorohexadecane as the substrate. Comparisons were made with the phospholipids of cells grown on n-hexadecane. Phosphatidylinositolmannosides and phosphatidylethanolamine (PE) were the major phospholipids in n-hexadecane-grown cells. In 1-chlorohexadecane-grown cells, phosphatidylinositolmannosides were approximately half of the total phospholipids, with lesser amounts of PE and cardiolipin (CL). The relative level of PE was greater at 20 degrees C (versus that at 30 degrees C) after growth on either substrate. A determination was made of structure and positional distribution of constituent fatty acid in both CL and PE. The relative amount of unsaturated fatty acid was higher at 20 degrees C. There were two C16:1 fatty acids (C16:1 delta 9 and C16:1 delta 11), and these had positional preferences in both CL and PE. The positional sites of chlorinated fatty acids differed in both CL and PE at the two temperatures. The results confirm that microorganisms can specifically distribute chlorinated fatty acids into cellular phospholipids.     

The incorporation of unsaturated fatty acids of the n-9, n-6, and n-3 families into individual phospholipids by isolated hepatocytes of thermally-acclimated rainbow trout, Salmo gairdneri

Rates of incorporation of 1-14C-oleic (18:1n9), -linoleic (18:2n6), and -linolenic (18:3n3) acids into individual phosphatides were determined in isolated hepatocytes from cold (5 degrees C)- and warm (20 degrees C)-acclimated rainbow trout, Salmo gairdneri. Fatty acid incorporation into phosphatidylcholine (PC) exceeded that into all other phospholipids, but at assay and acclimation temperatures of 5 degrees C, incorporation into phosphatidylethanolamine (PE) was generally intermediate between that of PC and the remaining phosphatides. Specific radioactivities (ratios of percentage isotope incorporation-to-mole percentage of phosphatide) were consistently less than one for both PC and PE, and greater than one for phosphatidic acid (PA), lysophosphatidylcholine (LPC), phosphatidylserine (PS), and cardiolipin (CL). For PS, specific radioactivities were greater in cold- than warm-acclimated trout, and greater at 5 degrees C than 20 degrees C. Rates of oleate incorporation were generally higher, and rates of incorporation of 18:2 and 18:3 lower in cold- than warm-acclimated trout. Most phospholipids demonstrated a clear preference for the incorporation of 18:2 when assayed at 20 degrees C; however, at 5 degrees C the incorporation of 18:2 was reduced and 18:3 was generally the preferred substrate. A reduction in assay temperature from 20 degrees C to 5 degrees C also shifted the incorporation of 18:2 away from PC into PS and PA. These data were interpreted to indicate 1) a cold-induced activation of PS metabolism, possibly resulting in elevated levels of PE; 2) lower rates of general acyl group turnover in animals acclimated to 5 degrees C than 20 degrees C; 3) a specificity to the acclimation response that favors the incorporation at cold temperatures of polyunsaturated fatty acids, but not the parent acids from which they are derived; and 4) the participation of a deacylation-reacylation cycle in the metabolism of phospholipids, particularly at cold temperatures.     

Perkinsus marinus, a protozoan parasite of the Eastern oyster (Crassostrea virginica): effects of temperature on the uptake and metabolism of fluorescent lipid analogs and lipase activities

The effects of temperature on the uptake and metabolism of fluorescent labeled palmitic acid (FLC16) and phosphatidylcholine (FLPC) and lipase activities in the oyster protozoan parasite, Perkinsus marinus, meront stage were tested at 10, 18, and 28 degrees C. Temperature significantly affected not only the uptake, assimilation, and metabolism of both FLC16 and FLPC in P. marinus, but also its triacylglycerol (TAG) lipase activities. The incorporation of both FLC16 and FLPC increased with temperature and paralleled the increase in the amount of total fatty acids in P. marinus meront cultures. The incorporation of FLC16 was higher than FLPC at all temperatures. The percentage of FLC16 metabolized to TAG was significantly higher at higher temperatures. Trace amounts of incorporated FLC16 were detected in monoacylglycerol (MAG) and PC at 18 and 28 degrees C. P. marinus meronts metabolized FLPC to TAG, diacylglycerol (DAG), monoacylglycerol (MAG), free fatty acids (FFA), phosphatidylethanolamine (PE), and cardiolipin (CL). The conversion of FLPC to TAG and PE was highest at 28 degrees C. The relative proportions of individual fatty acids and total saturated, monounsaturated and polyunsaturated fatty acids changed with temperatures. While total saturated fatty acids (SAFAs) increased with temperature, total monounsaturated fatty acids (MUFAs) decreased with temperature. Total polyunsaturated fatty acids (PUFAs) increased from 28 to 18 degrees C. The findings of increase of total SAFAs and decrease of total MUFAs with the increase of temperatures and upward shift of total PUFAs from 28 to 18 degrees C suggest that, as in other organisms, P. marinus is capable of adapting to changes in environmental temperatures by modifying its lipid metabolism. Generally, higher lipase activities were noted at higher cultivation temperatures. Both TAG lipase and phospholipase activities were detected in P. marinus cells and their extra cellular products (ECP), but phospholipase activities in both the cell pellets and ECP were very low. Also, lipase activities were much lower in ECP than in the cells. The observations of low metabolism, bioconversion of incorporated fluorescent lipid analogs and lipase activities at low temperatures are consistent with the low in vitro growth rate and low infectivity of P. marinus at low temperatures.     

Phospholipid composition of methane-utilizing bacteria.

The phospholipids of Methylococcus capsulatus, Methylosinus trichosporium, La Paz, and OBT were examined in relation to their qualitative and quantitative composition. M. capsulatus exhibited a phospholipid composition consisting of phosphatidylethanolamine, phosphatidylglycerol, cardiolipin, and phosphatidyl-choline. The esterified fatty acids were predominantly C16:0 and C16:1. M. trichosporium, La Paz, and OBT exhibited an essentially identical phospholipid composition consisting of phosphatidylmonomethylethanolamine, phosphatidyl-dimethylethanolamine, phosphatidylcholine, and phosphatidylglycerol. Only trace amounts (less than 1%) of cardiolipin were found in these organisms. The major esterified fatty acid in these organisms was C18:1 (87 to 90%). The monounsaturated fatty acids from all four organisms consisted of both cis and trans isomers, each of which contained delta8, delta9, delta10, and delta11 double-bond positional isomers.     

Effects of zinc on lipids of erythrocytes from carp (Cyprinus carpio L.) acclimated to different temperatures

We compared the effect of zinc (0.01, 0.1, 0.5 and 1 mM) at two temperatures (5 and 20 degrees C) on erythrocytes from summer and winter acclimatised carp. An increase in temperature from 5 to 20 degrees C increased the unsaturation index (UI) and relative proportion (UI/SFA) of unsaturated to saturated fatty acids in total lipids of the red cells. At 5 degrees C, the unsaturation index of phosphatidylcholine (PC), phosphatidylserine (PS), phosphatidylethanolamine (PE) and phosphatidylinositol (PI) decreased (30-40%) in the presence of 1 mM zinc. The change in unsaturation of phospholipids in the presence of zinc at 5 degrees C is probably responsible for the alteration in structural integrity of erythrocyte membrane as observed by hemolysis and the decreased thiol group content in the erythrocytes. In light of this result, zinc may be considered an environmental hazard for these fish at low temperatures.     

The hydrogenation of phospholipid-bound unsaturated fatty acids by a homogeneous, water-soluble, palladium catalyst

The hydrogenation of unsaturated phospholipids by palladium di(sodium alizarine monosulphonate) activated for 5 min under H2 proceeded rapidly at 20 degrees C and 1 atm. H2. Multibilayer liposomes of dioleoyl- and dilinolenoylphosphatidylcholine were hydrogenated at similar rates while dilinoleoyl- and 1-palmitoyl-2-oleoylphosphatidylcholine were hydrogenated at slightly slower rates. The reduction of polyunsaturated fatty acids gave rise to a variety of natural and unnatural positional cis and trans isomers which were largely reduced further to saturated fatty acids as the hydrogenation continued. Dioleoylphosphatidylethanolamine was attacked by the catalyst more slowly at 20 degrees C than was the equivalent phosphatidylcholine molecular species. Experiments conducted using mixtures of phosphatidylethanolamine and phosphatidylcholine in varying proportions also suggested that phospholipids are slightly more susceptible to catalytic hydrogenation in the bilayer phase than in the hexagonalII phase. Understanding the sequence of hydrogenation reactions involving these one and two component lipid preparations is useful in interpreting the action of the palladium catalyst on living cells under the same mild conditions.     

A trans-unsaturated fatty acid in a psychrophilic bacterium, Vibrio sp. strain ABE-1.

A high level of a trans-unsaturated fatty acid was found in the phospholipids of a psychrophilic bacterium, Vibrio sp. strain ABE-1. This fatty acid was identified as 9-trans-hexadecenoic acid (C16:19t) by gas-liquid chromatography and infrared absorption spectrometry. C16:1(9)t accounted for less than 1% of the total fatty acids in cells grown at 5 degrees C and reached 12% of the total at 20 degrees C. We suggest that the increase in the level of the trans-unsaturated fatty acid is related to the high growth rate of this bacterium at elevated temperatures. Possible biological roles of the trans-unsaturated fatty acid in the adaptation of the microorganism to the ambient temperature are discussed.     

Incorporation of exogenous fatty acids into phospholipids by cultured hamster fibroblasts. Effect of SV40 transformation

In situ incorporation of two saturated (palmitic, 16:0; stearic, 18:0) and three unsaturated fatty acids (oleic, 18:1; linoleic, 18:2; arachidonic, 20:4) into the four major phospholipids, sphingomyelin, PC, PI and PE, was followed. Transformed cells incorporated unsaturated fatty acids more rapidly, whereas no significant differences were found concerning saturated fatty acids. In vitro determination of phospholipid acylation showed that incorporation of coenzyme A-activated forms of two saturated fatty acids (16:0 and 18:0) and one unsaturated fatty acid (18:1) into phospholipids was increased in transformed cells. Comparison of results obtained in situ and in vitro strongly suggests that incorporation of fatty acids into phospholipids in cultured cells is not limited by acyltransferase activities.     

Modification of membrane lipid: physical properties in relation to fatty acid structure.

Differential scanning calorimetry (DSC) and electron spin resonance (ESR) measurements were made to characterize how modifications in the fatty acid composition of Escherichia coli affected the thermotropic phase transition(s) of the membrane lipd. When the fatty acid composition contained between 20 and 60% saturated fatty acids, the DSC curves for isolated phospholipids and cytoplasmic membranes showed a broad (15-25 degree C) gel to liquid-crystalline phase transition, the position of which depended on the particular fatty acid composition. Utilizing multiple lipid mutants, enrichment of the membrane phospholipids with a single long-chain cis-monoenoic fatty acid in excess of that possible in a fatty acid levels less than 20% and gradually replaced the broad peak as the cis-monoenoic fatty acid content increased. These results were obtained with phospholipids, cytoplasmic membranes, and whole cells. With these same phopholipids, plots of 2,2,6,6-tetramethylpiperidinyl-1-oxy partitioning and ESR order parameters vs. 1/T revealed discontinuities at temperatures 40-60 degrees C above the calorimetrica-ly measured gel to liquid-crystalline phase transitions. Moreover, when the membrane phospholipids were enriched with certain combinations of cis-monenoic fatty acids (e.g., cis-delta 9-16:1 plus cis-delta 11-18:1) the DSC curve showed a broad gel to liquid crystalline phase change below 0 degrees C but the ESR studies revealed no discontinuities at temperatures above those of the gel to liquid-crystalline transition. These results demonstrated that enrichment of the membrane lipids with molecules in which both fatty acyl chains are identical cis-monoenoic residues led to a distinct type of liquid-crystalline phase. Furthermore, a general conclusion from this study is that Escherichia coli normally maintains a heterogeneous mixture of lipid molecules and, by so doing, prevents strong lipid-lipid associations that lead to the formation of lipid domains in the membrane.     

Effects of clofibrate feeding on essential fatty acid desaturation and oxidation in isolated rat liver cells.

The effects of clofibrate feeding on the metabolism of polyunsaturated fatty acids were studied in isolated rat hepatocytes. Administration of clofibrate stimulated the oxidation and particularly the peroxisomal beta-oxidation of all the fatty acids used. The increase in oxidation products was markedly higher when n-3 fatty acids were used as substrate, indicating that peroxisomes contribute more to the oxidation of n-3 than n-6 fatty acids. The whole increase in oxidation could be accounted for by a corresponding decrease in acylation in triacylglycerol while the esterification in phospholipids remained unchanged. A marked stimulation of the amounts of newly synthesized C16 and C18 fatty acids recovered, was observed when 18:2(n-6), 20:3(n-6), 18:3 (n-3) and 20:5(n-3), but not when 20:4(n-6) and 22:4(n-6) were used as substrate. This agrees with the view that extra-mitochondrial acetyl-CoA produced from peroxisomal beta-oxidation is more easily used for fatty acid new synthesis than acetyl-CoA from mitochondrial beta-oxidation. The delta 6 and delta 5 desaturase activities were distinctly higher in cells from clofibrate fed rats indicating a stimulating effect.     

Synthetic lethal interaction of the mitochondrial phosphatidylethanolamine and cardiolipin biosynthetic pathways in Saccharomyces cerevisiae

Saccharomyces cerevisiae mitochondria contain enzymes required for synthesis of the phospholipids cardiolipin (CL) and phosphatidylethanolamine (PE), which are enriched in mitochondrial membranes. Previous studies indicated that PE may compensate for the lack of CL, and vice versa. These data suggest that PE and CL have overlapping functions and that the absence of both lipids may be lethal. To address this hypothesis, we determined whether the crd1delta mutant, which lacks CL, was viable in genetic backgrounds in which PE synthesis was genetically blocked. Deletion of the mitochondrial PE pathway gene PSD1 was synthetically lethal with the crd1delta mutant, whereas deletion of the Golgi and endoplasmic reticulum pathway genes PSD2 and DPL1 did not result in synthetic lethality. A 20-fold reduction in phosphatidylcholine did not affect the growth of crd1delta cells. Supplementation with ethanolamine, which led to increased PE synthesis, or with propanolamine, which led to synthesis of the novel phospholipid phosphatidylpropanolamine, failed to rescue the synthetic lethality of the crd1delta psd1delta cells. These results suggest that mitochondrial biosynthesis of PE is essential for the viability of yeast mutants lacking CL.     

Effect of lipid composition on the stability of cellular membranes during freeze-thawing of Lactobacillus acidophilus grown at different temperatures

Lactobacillus acidophilus CRL 640 grown at the optimal temperature of 37 degrees C (M37) appeared more sensitive to freeze-thawing than when it was grown at 25 degrees C (M25). In the first case, 87% of the cells died, in contrast to 33% for cells grown at 25 degrees C. All the surviving M37 cells showed sensitivity to NaCl. However, among the surviving M25 cells, only 85% were sensitive to NaCl. The rest of the cells were considered uninjured. Freeze-thawing in cells grown at 25 degrees C showed a liberation of nucleic acids and proteins. However, the leakage was higher in M37 cells after freeze-thawing. The greater fraction of damaged cells were observed in M25 culture after freeze-thawing. A relative increase of 81% in cardiolipid (CL), with respect to total phospholipids and 72% triglycosyldiglyceride (TGDG) with respect to the total glycolipids was observed in M37. In addition, a decrease of palmitoyl (C16:0), oleoyl (C18:0) fatty acids at CL, phosphatidylglycerol (PG), and diglicosyldiglyceride (DGDG) fractions and the increase of C19 cyc and C18:0, 10-OH fatty acids in neutral lipid, and CL fractions was also apparent. In M25 cells, the concentration of DGDG and PG was higher than in M37 cells. The difference in cryotolerance between the frozen cultures emphasizes the importance of selecting appropriate conditions of growth of microorganisms for use as dietary adjuncts.     

Assimilation of chlorinated alkanes by hydrocarbon-utilizing fungi.

The fatty acid compositions of two filamentous fungi (Cunninghamella elegans and Penicillium zonatum) and a yeast (Candida lipolytica) were determined after the organisms were grown on 1-chlorohexadecane or 1-chlorooctadecane. These organisms utilized the chlorinated alkanes as sole sources of carbon and energy. Analyses of the fatty acids present after growth on the chlorinated alkanes indicated that 60 to 70% of the total fatty acids in C. elegans were chlorinated. Approximately 50% of the fatty acids in C. lipolytica were also chlorinated. P. zonatum contained 20% 1-chlorohexadecanoic acid after growth on either substrate but did not incorporate C18 chlorinated fatty acids.     

Physical properties of murine fibroblasts with altered acyl chain unsaturation.

Murine fibroblasts, LM cells, were cultured in suspension with laurate (12:0), myristate (14:0), palmitate (16:0), palmitoleate (16:1), or palmitate + palmitoleate (16:0 + 16:1) bound to fatty acid-free bovine serum albumin. Supplementation with saturated fatty acids decreased the ratio of unsaturated/saturated fatty acids in membrane phospholipids as much as 3.4-fold (palmitate-enriched cells). Concomitantly fluorescence polarization, absorption-corrected fluorescence, and relative fluorescence efficiency of the fluorescence probe molecule, β-parinaric acid, increased 1.5-, 2.9-, and 1.8-fold, respectively, in the membrane phospholipids. Unsaturated fatty acid (palmitoleate) increased the unsaturated/saturated fatty acid ratio by 20% but did not significantly alter the fluorescence parameters. When the cells were fed mixtures of palmitate and palmitoleate, the unsaturated/saturated fatty acid ratio of the membrane phospholipids and the above fluorescence parameters had values intermediate between those if each fatty acid had been fed separately. All fatty acid supplements caused a loss of two characteristic temperatures in Arrhenius plots of relative fluorescence efficiency. However, no shifts or appearance of new characteristic temperatures occurred. The break points at approximately 42, 37, and 22 °C were essentially un-altered. The data were consistent with the possibility that LM cells were unable to maintain constant fluidity, as indicated by fluorescence polarization, when supplemented with different fatty acids. A good correlation could be made between the phospholipid unsaturated/ saturated fatty ratio, the fluorescence polarization, and the toxicity elicited by different fatty acid supplements.     

Thermotropic behavior of lipids and the morphology of Yersinia pseudotuberculosis cells with a high content of lysophosphatidylethanolamine

The content of lysophosphatidylethanolamine (LPE) in Y. pseudotuberculosis cells was found to increase during their growth at 8 degrees C under stationary conditions (without stirring the medium) and at 37 degrees C when the medium contained glucose. The maximum level of LPE (up to 45% of the total phospholipids) was observed in cells grown at 8 degrees C under stationary conditions. Such cells showed an enhanced growth rate, a reduced yield of biomass, an altered cell morphology, and an increased cell area. The cells contained unsaturated fatty acids, phosphatidylethanolamine (PE), and total phospholipids in small amounts, whereas neutral lipids and diphosphatidylglycerol were abundant. In addition, the cells contained an amount of methylated PE and phospholipids of unknown structure. Irrespective of whether the temperature for growth was low or high, the LPE-rich cells showed a high value (32-36 degrees C) of the maximum temperature of thermal transition of lipids (Tmax). This finding is indicative of a densification of the membrane lipid matrix of the LPE-rich cells. The suggestion is made that LPE is accumulated in glucose-fermenting bacterial cells in response to stress caused by oxygen deficiency and low pH values of the growth medium. The possible relationship between LPE accumulation and the virulence of Y. pseudotuberculosis cells grown at low temperatures is discussed.     

Changes in lipid fluidity and fatty acid composition with altered culture temperature in Tetrahymena pyriformis-NT1

Cultures of T. pyriformis-NT1 were grown at 20 degrees C (Tg 20 degrees C) and 38 degrees C (Tg 38 degrees C). G.L.C. analysis and D.P.H. fluorescence polarization measurements in extracted phospholipids indicated that there was increased saturation of fatty acids and relatively reduced fluidity as growth temperature was increased. Breakpoints occurred in the Arrhenius plots of fluorescence polarization at 16 degrees C for Tg 38 degrees C total extracted phospholipids and 9 degrees C for Tg 20 degrees C lipids.     

The effects of growth temperature on the methyl sterol and phospholipid fatty acid composition of Methylococcus capsulatus (Bath)

Growth of Methylococcus capsulatus (Bath) at temperatures ranging from 30 to 50 degrees C resulted in changes to the whole cell lipid constituents. As temperature was lowered, the overall proportion of hexadecenoic acid (C16:1) increased, and the relative proportions of the delta 9, delta 10 and delta 11 C16:1 double bond positional isomers changed. Methyl sterol content also increased as the growth temperature was lowered. The highest amounts of methyl sterol were found in 30 degrees C cells and the lowest in 50 degrees C cells (sterol-phospholipid ratios of 0.077 and 0.013, respectively). The data are consistent with a membrane modulating role for the sterol produced by this prokaryotic organism.     

The effects of temperature on the fatty acid and phospholipid composition of four obligately psychrophilicVibrio Spp.

The free fatty acid and phospholipid composition of 4 psychrophilic marineVibrio spp. have been determined in chemostat culture with glucose as the limiting substrate over a temperature range 0–20°C. All the isolates show maximum glucose and lactose uptake at 0°C and this correlates with maximum cell yield. None of the isolates contain fatty acids with a chain length exceeding 17 carbon atoms.Vibrio AF-1 andVibrio AM-1 respond to decreased growth temperatures by synthesizing increased proportions of unsaturated fatty acids (C15:1, C16:1 and C17:1) whereas inVibrio BM-2 the fatty acids undergo chain length shortening. The fourth isolate (Vibrio BM-4) contains high levels (60%) of hexadecenoic acid at all growth temperatures and the fatty acid composition changes little with decreasing temperature. The principal phospholipid components of the four psychrophilic vibrios were phosphatidylserine, phosphatidylglycerol, phosphatidylethanolamine and diphosphatidylglycerol. Lyso-phosphatidylethanolamine and 2 unknown phospholipids were additionally found inVibrio AF-1. The most profound effect of temperature on the phospholipid composition of these organisms was the marked increase in the total quantities synthesized at 0°C. At 15°C phosphatidylglycerol accumulated in the isolates as diphosphatidylglycerol levels decreased. Additionally inVibrio BM-2 andVibro BM-4 phosphatidylserine accumulates as phosphatidylethanolamine biosynthesis was similarly impaired. The observed changes in fatty acid and phospholipid composition in these organisms at 0°C may explain how solute transport is maintained at low temperature.Abbreviations PS Phosphatidylserine - PE phosphatidylethanolamine - PG phosphatidylglycerol - DPG diphosphatidylglycerol - lyso PE lysophosphatidylethanolamine     

Studies on the endogenous phospholipids of mammalian kidney and their in vitro hydrolysis by endogenous phospholipases: a thin layer chromatographic and densitometric study

The phosphoglycerides profile of six species of mammalian kidney (guinea pig, pig, cat, dog, mouse and rat) and their in vitro response to the endogenous phospholipases were determined by TLC technology in conjunction with densitometric measurements. Changes in their phospholipids profile subsequent to in vitro incubation of whole tissue homogenate of these kidneys for 60 min, at pH 7.4, 38 degrees C, and prior to phospholipids extraction have shown that the deacylation of the endogenous cardiolipin (CL) is the most prevalent lipolytic event of all mammalian kidneys studied. Concurrent with the deacylation of CL, there was also formation of monolysocardiolipin (MLCL) and a reduction in CL level. To a much lesser extent, lyso alkenyl phosphatidyl ethanolamine (LPE) was also produced concomitant with a decrease of the endogenous alkenyl phosphatidyl ethanolamine (PE) level. The deacylation of PE plasmalogen to its lyso form confirms the action of endogenous PLA(2) releasing sn-2 fatty acids.     

Apparent relative retention of the phosphatidylethanolamine molecular species 18:0-20:5(n-3), 16:0-22:6(n-3) and the sum 16:0-20:4(n-6) plus 16:0-20:3(n-9) in the liver microsomes of pig on an essential fatty acid deficient diet.

Attempts at a better understanding of the cell membrane organization and functioning need to assess the physical properties which partly depend (i) on the positional distribution of the fatty acids in the membrane phospholipids (PLs) and (ii) on the way by which the PL molecular species are affected by exogenous fatty acids. To do that, the effects of essential (polyunsaturated) fatty acid (EFA) deficiency and enrichment were studied in the liver microsomes of piglets feeding on either an EFA-deficient diet or an EFA-enriched diet containing hydrogenated coconut oil or a mixture of soya + corn oils, respectively. After derivatization, the diacylated forms of choline and ethanolamine PLs were analyzed using a combination of chromatographic techniques and fast-atom bombardment-mass spectrometry. The dinitrobenzoyl-diacylglycerol derivatives corresponding to the molecular species of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were identified. It appears that three factors brought about a marked apparent relative retention: the nature of (i) the base of the polar head, (ii) fatty acids at the sn-1 position and (iii) fatty acids at the sn-2 position. The highest apparent relative retentions were displayed by the 18:0-20:5(n-3)-PE and 16:0-22:6(n-3)-PE. It is noteworthy that the behavior of 20:3 n-9--which is synthesized during the EFA-deficient diet by the same bioconversion system as 20:4 n-6--was very similar to that of 20:4 n-6 during the formation of PC and PE molecular species and that the molecular species of PE containing 20:4(n-6) and 20:3(n-9), gathered together as metabolical homologues, were also apparently retained, particularly in association with 16:0. Present observations are consistent with some others showing retention or preferential distribution of EFA in PE and suggest that specific acyltransferase(s), ethanolamine phosphotransferase and methyltransferase would be mainly involved for PE and PC formation in liver endoplasmic reticulum. Fast-atom bombardment-mass spectrometry of intact phospholipids enables us to show that there is no very long chain dipolyunsaturated phospholipid in liver endoplasmic reticulum.