Lipid composition and metabolism in oospores and oospheres ofAchlya americana

Oospores and oospheres ofAchlya americana Humphrey were isolated by sonication and filtration through nylon-mesh cloth of progressively diminishing porosity, and their lipid composition was investigated. The average dry weight of an oospore was 3.2 ng. Approximately 37% of the dry weight was composed of lipid. Triacylglycerols represented 88.7% of the total lipid, unesterified fatty acids made up 9.7%, and sterols, sterol esters, phospholipids, and mono- and diacylglycerols each constituted less than 1% of the total. Palmitic, oleic, and linoleic acids were the predominant fatty acids, along with smaller amounts of myristic, palmitoleic, stearic, arachidonic, and eicosapentaenoic acids. The fatty acid composition of the triacylglycerol fraction was similar to that of the total lipid, while that of the phospholipid fraction was higher in oleic acid. The unesterified fatty acid fraction was higher in saturated components than the total lipid, while the sterol ester fraction was higher in unsaturated fatty acids. In both the total lipid and the various lipid classes, unsaturated fatty acids increased during spore development. The sterol fraction consisted of 72% fucosterol, 22% cholesterol, and 7% 24-methylenecholesterol. In both oospheres and oospores, 1-[¹⁴C] acetate was assimilated most readily into phospholipids, triacylglycerols, and unesterified fatty acids, and was incorporated preferentially into palmitic, palmitoleic, and oleic acids. 1-[¹⁴C]-Arachidonic acid was incorporated by isolated oospheres into eicosapentaenoic acid, indicating that arachidonic acid is the immediate precursor of eicosapentaenoic acid.     

Effects of cold adaptation and re-adaptation upon the mitochondrial phospholipids of brown adipose tissue.

1. A study of the mitochondrial phospholipids, phospholipid fatty acid patterns and enzyme activities was investigated in brown tissue (B.A.T.) from rats chronically exposed to cold and/or treated with thyroxine. 2. The total activities of the oxidative enzymes were increased after cold exposure, but not after thyroxine treatment. 3. Cold exposure increased the amount of phosphatidylethanolamine, phosphatidylcholine, cardiolipin and lysophospholipids, the effect being greatest for phosphatidylethanolamine. At the same time, there were marked alterations in the fatty acid composition of the mitochondrial phospholipids (decrease of palmitic, palmitoleic and oleic acids ; increase of stearic, linoleic and arachidonic acids). 4. All these cold-induced alterations were reversed by re-adaptation of the animal to a normal temperature range. 5. The alterations of the fatty acid composition of phospholipids could be explained by changes in the rate of individual fatty acid biosynthesis.     

Cholesterol esters in developing rat brain: concentration and fatty acid composition

Abstract— The contents and the fatty acid composition of cholesterol esters were analysed in developing rat brain. The total content did not exceed 20 μg/brain throughout development. Elimination of serum by adequate perfusion was essential for accurate results. Two separate events appeared to affect the levels of cholesterol esters in developing rat brain, one probably reflecting general developmental changes and the other apparently related to myelination. On either a unit weight or a whole brain basis, the curves appeared to be a superimposition of the two events. There was an underlying developmental change, which was characterized on a unit weight basis by the highest level of cholesterol esters immediately after birth and a steady decline to the adult level by 30 days of age or which on the basis of whole brain was characterized by a steady increase throughout the development. A period of transient increase was superimposed on this underlying developmental change between the ages of 7 and 27 days and corresponded to the period of active myelination. The major fatty acids of rat brain cholesterol esters were palmitic, palmitoleic, oleic and arachidonic acids. Palmitic and palmitoleic acids decreased in proportion while oleic acid increased, as the animal matured. The fatty acid composition of serum cholesterol esters was distinctly different from that of brain cholesterol esters; those from serum contained much higher proportions of linoleic and arachidonic acids and much less palmitoleic and oleic acids.     

Changes in the fatty acid profiles of red blood cell membrane phospholipids in human neonates during the first month of life

We have studied the changes in the fatty acid profiles of red blood cell membrane phospholipids in 47 infants who were exclusively fed human milk from birth to 1 month of life. Twenty blood samples were obtained from cord, 15 at 7 days and 12 at 30 days after birth. Membrane phospholipids were obtained from erythrocyte ghosts by thin-layer chromatography and fatty acid composition was determined by gas liquid chromatography. Phosphatidylcholine showed the most important changes during early life; stearic, w6 eicosatrienoic and arachidonic acids decreased whereas oleic and linoleic acids increased. In phosphatidylethanolamine, palmitic and stearic acid declined and oleic, linoleic and docosahexenoic acids increased with advancing age. Small changes were noted for individual fatty acids in phosphatidylserine. In sphingomyelin stearic acid increased from birth to 1 month and linoleic, arachidonic and nervonic acids decreased. Total polyunsaturated fatty acids of the w6 series greater than 18 carbon atoms increased with advancing age in phosphatidylethanolamine and decreased in choline and serine phosphoglycerides and in sphingomyelin. Long chain fatty acids derived from linoleic acid decreased in phosphatidylcholine but increased in ethanolamine and serine phosphoglycerides. The different behavior in the changes observed in fatty acid patterns for each erythrocyte membrane phospholipid may be a consequence of its different location in the cell membrane bilayer and specific exchange with plasma lipid fractions.     

Effects of postnatal age and diet on the fatty acid composition of plasma lipid fractions in preterm infants

Diet and postnatal age effect the fatty acid composition of plasma and tissue lipids. This work was designed as a transversal study to evaluate the changes in the fatty acid composition of plasma phospholipids, cholesteryl esters, triglycerides and free fatty acids in preterm infants (28-35 weeks gestational age), fed human milk (HM) and milk formula (MF) from birth to 1 month of life. Sixteen blood samples were obtained from cord, and 19 at 6-8 h after birth, 14 at 1 week and 9 at 4 weeks from HM-fed infants and 18 at 1 week and 14 at 4 weeks from MF-fed ones. Groups had similar mean birth weight, gestational age and sex ratio. The MF provided 69 kcal/dl and contained 16% of linoleic acid and 1.3% of alpha-linolenic acid on the total fat. Plasma lipid fractions were extracted and separated by thin-layer chromatography and fatty acid methyl esters were quantitated by gas liquid chromatography. In plasma phospholipids, linoleic acid (18:2 omega 6) continuously increased from birth to 1 month of age, but no changes were seen as related to type of diet; polyunsaturated fatty acids greater than 18 carbon atoms of both the omega 6 and omega 3 series (PUFA omega 6 greater than 18 C and omega 3 greater than 18 C) dropped from birth to 1 week and continued to decrease in MF-fed infants until 1 month; eicosatrienoic (20:3 omega 6), arachidonic (20:4 omega 6) and docosahexaenoic (22:6 omega 3) were the fatty acids implicated. In cholesteryl esters palmitoleic (16:1 omega 7) and oleic (18:1 omega 9) acids decreased from birth to 1 month and linoleic acid increased and arachidonic acid dropped, especially in MF fed infants. In triglycerides, palmitic, palmitoleic and stearic acid (18:0) decreased during the first month of life; oleic acid remained constant and linoleic acid increased in all infants, but arachidonic acid decreased only in those fed formula. Free fatty acids showed a similar behavior in fatty acids and in plasma triglycerides. Preterm neonates seem to have special requirements of long-chain PUFA and adapted MF should contain these fatty acids in similar amounts to those of HM to allow the maintenance of an adequate tissue structure and physiology.     

Fatty acid changes in liver and plasma lipid fractions after safflower oil was fed to rats deficient in essential fatty acids

1. Fatty acid patterns of liver and plasma triglycerides, phospholipids and cholesteryl esters were determined at intervals during 24hr. after essential fatty acid-deficient rats were given one feeding of linoleate (as safflower oil). 2. Liver triglyceride, phospholipid and cholesteryl ester fatty acid compositions did not change up to 7hr. after feeding. Between 7 and 10hr., linoleic acid began to increase in all fractions, but arachidonic acid did not begin to rise in the phospholipid until 14-19hr. after feeding. 3. Oleic acid and eicosatrienoic acid in liver phospholipid began to decline at about the time that linoleic acid increased, i.e. about 9hr. before arachidonic acid began to increase. 4. Changes in linoleic acid, arachidonic acid and eicosatrienoic acid in phosphatidylcholine resembled those of the total phospholipid. Phosphatidylethanolamine had a higher percentage content of arachidonic acid before the linoleate was given than did phosphatidylcholine, and after the linoleate was given the fatty acid composition of this fraction was little changed. 5. The behaviour of the plasma lipid fatty acids was similar to that of the liver lipids, with changes in linoleic acid, eicosatrienoic acid and arachidonic acid appearing at the same times as they occurred in the liver. 6. The results indicated that linoleic acid was preferentially incorporated into the liver phospholipid at the expense of eicosatrienoic acid and oleic acid. The decline in these fatty acids apparently resulted from their competition with linoleic acid for available sites in the phospholipids rather than from any direct replacement by arachidonic acid.     

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.     

Fatty acid composition of serum lipids in bilharzial hepatic fibrosis and chronic active hepatitis.

The fatty acid pattern of blood serum lipids was examined by gas liquid-chromatography in 30 cases with bilharzial hepatic fibrosis, 11 cases with chronic active hepatitis accompanied by jaundice, and 28 healthy individuals as a comparison group of the same socioeconomic class of patients. In addition, the fatty acid patterns of the three major serum lipid classes, namely: cholesterol ester, phospholipids and triglycerides, were also investigated in seven cases of each group by gas liquid chromatography. The most remarkable differences were: a depression of the essential fatty acid level (linoleic and arachidonic) in both groups of patients together with a concomitant elevation of oleic acid in the bilharzial group and an elevation of oleic, palmitic, palmitoleic acids in the chronic active hepatitis group. The depression of linoleic and arachidonic acids was explained by the low fat diet intake, malnutrition, and the malabsorption factors which were frequent in all the patients studied. The elevation of monoethenoid acids was attributed to the decrease in the ability of the liver to desaturate the endogenous saturated and monounsaturated acids to polyunsaturated ones.     

Evidence for a Composite State of an F′his,gnd Element and a Cryptic Plasmid in a Derivative of Salmonella typhimurium LT2

The zoospores of Blastocladiella emersonii, when derived from cultures grown on solid media, contain about 11% total lipid. This lipid was separated chromatographically on silicic acid into neutral lipid (46.6%), glycolipid (15.8%), and phospholipid (37.6%). Each class was fractionated further on columns of silicic acid, Florisil, or diethylaminoethyl-cellulose, and monitored by thin-layer chromatography. Triglycerides were the major neutral lipids, mono- and diglycosyldiglycerides were the major glycolipids, and phosphatidylcholine and phosphatidylethanolamine were the major phospholipids. Other neutral lipids and phospholipids detected were: hydrocarbons, free fatty acids, free sterols, sterol esters, diglycerides, monoglycerides, lysophosphatidylcholine, lysophosphatidylethanolamine, phosphatidic acid, phosphatidylserine, and phosphatidylinositol. Palmitic, palmitoleic, stearic, oleic, gamma-linolenic, and arachidonic acids were the most frequently occurring fatty acids. When B. emersonii was grown in (14)C-labeled liquid media, lipid again accounted for 11% of both mature plants and zoospores released from them. The composition of the lipid extracted from such plants and spores was also the same; however, it differed markedly from that of the lipid in spores harvested from solid media, consisting of 28.3% neutral lipid, 12.0% glycolipid, and 59.7% phospholipid. The major lipids were again triglycerides for neutral lipids, mono- and diglycosyldiglycerides for glycolipids, and phosphatidyl choline and phosphatidylethanolamine for phospholipids.     

Metabolism of n-3 polyunsaturated fatty acids and modification of phospholipids in cultured rabbit aortic smooth muscle cells

The metabolism of the linolenic acid family (n-3) of fatty acids, e.g., linolenic, eicosapentaenoic, and docosahexaenoic acids, in cultured smooth muscle cells from rabbit aorta was compared to the metabolism of linoleic and arachidonic acids. There was a time-dependent uptake of these fatty acids into cells for 16 hr (arachidonic greater than docosahexaenoic, linoleic, eicosapentaenoic greater than linolenic), and the acids were incorporated mainly into phospholipids and triglycerides. Eicosapentaenoic and arachidonic acids were incorporated more into phosphatidylethanolamine and phosphatidylinositol plus phosphatidylserine and less into phosphatidylcholine than linolenic and linoleic acids. Docosahexaenoic acid was incorporated into phosphatidylethanolamine more than linolenic and linoleic acids and into phosphatidylinositol plus phosphatidylserine less than eicosapentaenoic and arachidonic acids. Added linolenic acid accumulated mainly in phosphatidylcholine and did not decrease the arachidonic acid content of any phospholipid subfraction. Elongation-desaturation metabolites of linoleic acid did not accumulate. Cells treated with eicosapentaenoic acid accumulated both eicosapentaenoic and docosapentaenoic acids mainly in phosphatidylethanolamine and the arachidonic acid content was decreased. Added docosahexaenoic acid accumulated mainly in phosphatidylethanolamine and decreased the content of both arachidonic and oleic acids. The following conclusions are drawn from these results. The three n-3 fatty acids are utilized differently in phospholipids. The arachidonic acid content of phospholipids is reduced by eicosapentaenoic and docosahexaenoic acids, but not by linolenic acid. Smooth muscle cells have little or no desaturase activity, but have significant elongation activity for polyunsaturated fatty acids.     

Lipid composition of miniature pig platelets

1. Analyses of platelet lipid composition were carried out on material pooled from male and female miniature pigs. 2. The cholesterol/phospholipid molar ratio was 0.6. 3. Phosphatidylcholine represents the major class of phospholipids (47%) and phosphatidylinositol the minor (2%). 4. The main fatty acids of phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol and sphingomyelin were: palmitic, stearic, oleic, linoleic and arachidonic acids. 5. The ratios of saturated to unsaturated fatty acids were: sphingomyelin, 1.7; phosphatidylcholine, 1.2; phosphatidylserine, 0.9; phosphatidylethanolamine and phosphatidylinositol, 0.6. 6. Our results suggests that human and miniature pig platelet lipids bear several characteristics in common. This fact would allow miniature pig to be used as a new experimental model.     

Dietary fat saturation produces lipid modifications in peritoneal macrophages of mouse

We investigated the effects of a saturated fat diet on mice lipid metabolism in resident peritoneal macrophages. Male C57BL/6 mice were weaned at 21 days of age and assigned to either the experimental diet, containing coconut oil (COCO diet), or the control diet, containing soybean oil as fat source. Fat content of each diet was 15% (w/w). Mice were fed for 6 weeks until sacrifice. In plasma of mice fed the COCO diet, the concentration of triglyceride, total cholesterol, HLD- and (LDL+VLDL)-cholesterol, and thiobarbituric acid-reactive substances (TBARS) increased, without changes in phospholipid concentration, compared with the controls. In macrophages of COCO-fed mice, the concentration of total (TC), free and esterified cholesterol, triglyceride, phospholipid (P) and TBARS increased, while the TC/P ratio did not change. The phospholipid compositions showed an increase of phosphatidylcholine and phosphatidylserine + phosphadytilinositol, a decrease of phosphatidylethanolamine, and no change in phosphatidylglycerol. (3)H(2)O incorporation into triglyceride and phospholipid fractions of macrophages increased, while its incorporation into free cholesterol decreased. Incorporation of [(3)H]cholesterol into macrophages of COCO-fed mice and the fraction of [(3)H]cholesterol ester increased. COCO diet produced an increase in myrystic, palmitic and palmitoleic acids proportion, a decrease in linoleic and arachidonic acids and no changes in stearic and oleic acids, compared with the control. Also, a higher relative percentage of saturated fatty acid and a decrease in unsaturation index (p <0.001) were observed in macrophages of COCO-fed mice. These results indicate that the COCO-diet, high in saturated fatty acids, alters the lipid metabolism and fatty acid composition of macrophages and produces a significant degree of oxidative stress.     

Fatty acid composition in native and cultured human endothelial cells

Endothelial cells from human umbilical veins were isolated by collagenase treatment. Cells were cultured in the presence of either 20% fetal bovine serum (FBS) or 20% human serum (HS). At confluency, endothelial cell lipids were labeled with tracer concentrations of tritiated arachidonic acid, then extracted and separated into lipid subclasses by thin layer chromatography. The fatty acid composition of each lipid class was determined by glass capillary gas-liquid chromatography analysis and compared to that of cells freshly isolated from the cord (NC cells). The fatty acid compositions differed only in phospholipids. Polyunsaturated fatty acids (PFAs), arachidonic, and linoleic acids were depleted in FBS cell phospholipids and replaced by both stearic and oleic acids. No significant difference could be observed between NC cell and HS cell phospholipids. We conclude that PFAs might be decreased in FBS cells because of the relative paucity of PFAs in FBS as compared to HS. It seems therefore more convenient to cultivate endothelial cells in the presence of HS, especially in respect to their phospholipid content of arachidonic acid, which is the physiological reservoir for prostacyclin synthesis.     

CHANGES IN CEREBRAL CORTICAL LIPIDS IN COBALT-INDUCED EPILEPSY

Abstract– In control rats and in rats rendered epileptic by insertion of cobalt slivers into the cerebral cortex, total free fatty acids, free cholesterol, esterified cholesterol, triglycerides and phospholipids were measured in normal and lesion areas of cerebral cortex. The cortical lipid profile of the adult rat resembled that of the whole brain of very young rats rather than that of adult whole brain, with the principal differences from whole adult brain being lower total lipid content, increased proportions of phosphatidyl choline in the phospholipid fraction, and higher levels of cholesterol esters. Cobalt-induced epilepsy was associated with significant changes in cerebral cortical lipids in the area of the lesion and in the non-necrotic tissue adjacent to the lesion. The total lipid in the area of the lesion decreased sharply as a result of reductions in free cholesterol and total phospholipids. The levels of cholesterol esters and triglycerides increased in the area of the lesion, and cholesterol esters were also increased in the adjacent tissue. In addition there were decreases in the proportion of phosphatidyl ethanolamine in the phospholipids from the lesion site and adjacent tissue and decreases in the proportions of oleic, arachidonic and nervonic acids (unsaturated acids), and an increase in the proportions of lignoceric acid in the phospholipids. In the site of the lesion only, we observed a decrease in phospholipid palmitic acid and an appreciable increase in the proportions of an unidentified long-chained fatty acid.     

Effects of oleic acid and its congeners,elaidic and stearic acids,on the structural properties of phosphatidylethanolamine membranes

Fatty acid derivatives are abundant in biological membranes, mainly as components of phospholipids and cholesterol esters. Their presence, free or bound to phospholipids, modulates the lipid membrane behavior. The present study shows the differential influence of the C-18 fatty acids (FAs), oleic, elaidic, and stearic acids on the structural properties of phosphatidylethanolamine (PE). X-ray diffraction of PE-FA systems demonstrated that oleic acid (OA) produced important concentration-dependent alterations of the lipid membrane structure: it induced reductions of up to 20-23 degrees C in the lamellar-to-hexagonal transition temperature of 1-palmitoyl-2-oleoyl PE and dielaidoyl PE and regulated the dimensions of the hexagonal lattice. In contrast, elaidic and stearic acids did not markedly alter the phospholipid mesomorphism. The above effects were attributed to the different "molecular shape" of OA (with a kink at the middle of the molecule) with respect to their congeners, elaidic and stearic acids. The effects of free fatty acids (FFAs) on membrane structure are relevant for several reasons: i) some biological membranes contain very high levels of FFAs. ii) Mediterranean diets with high OA intake have been shown to exert protective effects against tumoral and hypertensive pathologies. iii) FFA derivatives have been developed as antitumoral and antihypertensive drugs.     

Effects of acclimation temperature on membrane phospholipids in the flesh fly Sarcophaga similis

Cold acclimation is a well‐known strategy for enhancing cold tolerance in ectotherms including insects. Nevertheless, information on the physiological mechanisms underpinning this phenomenon is still limited. Biological membrane integrity is critical for insects to perform at low temperatures, and an advantage is conferred on those insects that can adjust the composition of their membrane phospholipids. Such changes contribute to homeoviscous adaptation, a process that allows membranes to maintain a liquid–crystalline (fluid) state at low temperatures. Here we investigated phospholipids in the flesh fly Sarcophaga similis acclimated to various temperatures. Significant differences were observed in the composition of their fatty acyl chains: flies acclimated to low temperatures showed a higher proportion of palmitic and oleic acids at the expense of palmitoleic acid. Other fatty acids (stearic, linoleic, linolenic, arachidonic, eicosapentaenoic acids) were not significantly changed. The degree of unsaturation decreased in cold‐acclimated flies, but the difference was quite small. The weighted average chain length and number of double bonds were unchanged among flies acclimated to different temperatures. As temperatures decreased, the percentage of phosphatidylethanolamine increased to twice that of phosphatidylcholine. We discuss the role of these phospholipid changes in cold acclimation.     

Characterization of the constituent fatty acids in phosphatidylinositol during early development in Rana nigromaculata

1. Qualitative and quantitative changes in phosphatidylinositol (PI) were analyzed in the eggs, embryos and tadpoles of the Japanese pond frog, Rana nigromaculata, at various stages of development. 2. The weight percentage of PI to total phospholipid and lipid was about 8.4-15.2% and 1.4-2.6%, respectively, during embryonic life. 3. At the early stages of the unfertilized egg and the two-cell embryo, the predominant fatty acids are palmitic, stearic, oleic and linoleic acid. From the dorsal lip, early gastrula stage and beyond, the percentage of linoleic acid declines and there is an increase in palmitoleic acid. A relatively large amount of arachidonic acid was noted at the unfertilized egg stage at the 1-position. 4. A large amount of arachidonic acid was also observed at the 2-position of PI in the unfertilized egg, hatching embryo and post-hatching tadpole stages, relative to palmitic and stearic acid. 5. Palmitic and stearic acid were increased at the 2-position of PI in the other embryo and the feeding tadpole stages, relative to arachidonic acid, indicating a shift in these molecular species. 6. Thus, there were marked changes in the positional distribution of the constituent fatty acids in PI during early development of R. nigromaculata.     

Sex differences in plasma cholesterol-esterifying activity in rats

Esterification of free cholesterol was investigated after incubation at 37 degrees C of plasma from immature and adult rats of both sexes kept on stock, fat-free, or cholesterol-supplemented diets. According to measurements of the decrease in free cholesterol, plasma from the fat-deficient rats showed the highest cholesterol-esterifying activity. Esterification was higher in the mature female rats than in the mature males on stock or cholesterol-containing diets, although no sex differences were observed in the sexually immature young or in the fat-free animals. There were no sex differences in the fatty acid composition of the plasma sterol esters, phospholipids, and triglycerides in the immature animals, but arachidonic acid increased at the expense of linoleic acid in the sterol ester fraction in the adult female (not, however, in the adult male). In the phospholipid fraction the higher ratio of palmitic to stearic acids in the male was confirmed. There was an increase in linoleic acid in all three plasma lipid fractions of the mature male after cholesterol feeding. It is suggested that cholesterol may inhibit the conversion of linoleate to arachidonate. During the incubation of plasma, there was little change in the distribution of fatty acids except for a decrease in palmitoleate, and increases in C(20) tri- and tetraenoic acids, in the sterol esters of mature female rats on the stock ration and the fat-free diet. These C(20) acids decreased concomitantly in the phospholipid fraction, as the transesterification reaction mechanism proposed by earlier workers would predict.     

Phospholipid metabolism, calcium flux, and the receptor-mediated induction of chemotaxis in rabbit neutrophils

Rabbit neutrophils were stimulated with the chemotactic peptide fMet-Leu-Phe in the presence of the methyltransferase inhibitors homocysteine (HCYS) and 3-deazaadenosine (3-DZA). HCYS and 3-DZA inhibited chemotaxis, phospholipid methylation, and protein carboxymethylation in a dose-dependent manner. The chemotactic peptide-stimulated release of [14C]arachidonic acid previously incorporated into phospholipid was also partially blocked by the methyltransferase inhibitors. Stimulation by fMet-Leu-Phe or the calcium ionophore A23187 caused release of arachidonic acid but not of previously incorporated [14C]-labeled linoleic, oleic, or stearic acids. Unlike the arachidonic acid release caused by fMet-Leu-Phe, release stimulated by the ionophore could not be inhibited by HCYS and 3-DZA, suggesting that the release was caused by a different mechanism or by stimulating a step after methylation in the pathway from receptor activation to arachidonic acid release. Extracellular calcium was required for arachidonic acid release, and methyltransferase inhibitors were found to partially inhibit chemotactic peptide-stimulated calcium influx. These results suggest that methylation pathways may be associated with the chemotactic peptide receptor stimulation of calcium influx and activation of a phospholipase A2 specific for cleaving arachidonic acid from phospholipids.     

Lipids of whole cells and plasma membrane fractions from Balb/c3T3, SV3T3, and concanavalin A-selected revertant cells.

The lipid composition of Balb/c3T3, SV3T3, and the concanavalin A-selected SV3T3 revertant cells has been analyzed at the whole cell and plasma membrane levels. In comparison to untransformed 3T3 whole cells, SV3T3 cells showed an unchanged content of triacylglycerols, free fatty acids, and glycerylether diesters but a lower concentration of total phospholipids, while no significant difference was found in the phospholipid composition. Whole SV3T3 revertant cells exhibited a lipid composition similar to that in untransformed 3T3 cells with the exception of a higher proportion of sphingomyelin. Analysis of isolated plasma membranes did not reveal any significant differences in the cholesterol to phospholipid molar ratio between 3T3 and SV3T3 or SV3T3 revertant cells. The major changes in the acyl chain pattern SV3T3 compared with whole 3T3 cells consisted of an increase of oleic and palmitoleic acids coupled with a decrease of C20 and C22 polyunsaturated acids in phosphatidylethanolamine and phosphatidylcholine; an increase of oleic acid was also evident in SV3T3 phosphatidylinositol plus phosphatidylserine. An increase of palmitoleic and oleic acids together with a decrease of arachidonic acid was also found in phosphatidylethanolamine of SV3T3 plasma membranes; the only change in SV3T3 plasma membrane phosphatidylcholine was an increase of oleic acid. An increase of monoenoic acids together with a decrease of arachidonic acid was also found in phosphatidylethanolamine, phosphatidylcholine, and phosphatidylinositol plus phosphatidylserine of SV3T3 revertant cells at the level of both whole cells and plasma membranes.