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.     

Insulin inhibits changes in the phospholipid profiles in sciatic nerves from streptozocin-induced diabetic rats: A phosphorus-31 magnetic resonance study

Sciatic nerve phospholipids obtained from insulin-treated streptozocin-induced diabetic, non-treated streptozocin-induced diabetic, and healthy, control male Sprague-Dawley rats after eighteen weeks of diabetes were studied by ³¹P NMR spectrometry. Eleven phospholipids resonances were identified as follows: Phosphatidic acid (Chemical shift, 0.30 ppm), dihydrosphingomyelin (0.13 ppm), ethanolamine plasmalogen (0.07 ppm), phosphatidylethanolamine (0.03 ppm), phosphatidylserine (−0.05 ppm), sphingomyelin (−0.09 ppm), lysophosphatidylcholine (−0.28 ppm), phosphatidylinositol (−0.30 ppm), alkylacylglycerophosphorylcholine (−0.78 ppm), choline plasmalogen (−0.80 ppm), and phosphatidylcholine (−0.84 ppm). Diabetic rats showed that phosphatidylcholine was significantly elevated p > 0.05, and ethanolamine plasmalogen and choline plasmalogen were significantly lower when compared with both control and insulin treated rats. The choline ratio (choline-containing phospholipids over noncholine phospholipids) was significantly elevated in the diabetic group, when compared with both control and insulin-treated groups. The ethanolamine ratio (ethanolamine-containing phospholipids over nonethanolamine phospholipids) and the ratio of the ethanolamine ratio over the choline ratio, was significantly elevated in the control and the insulin-treated groups when compared with the diabetic group. The presence of phosphatidic acid and the significance in phosphatidylcholine and ethanolamine plasmalogen, suggested that insulin had a role in the phosphatidylcholine metabolism in the rat nerve.     

LIPID COMPOSITION AND METABOLISM OF CULTURED HAMSTER BRAIN ASTROCYTES

Abstract— The lipid composition and metabolism of confluent cultures of cells derived from newborn hamster brain and having morphology characteristic of immature astrocytes or spongioblasts was investigated and compared to that of newborn hamster brain dispersions and cloned glioma cells (C6). The cells displayed stable morphology for at least 30 subcultures; thereafter spontaneous transformation occurred. No appreciable changes were observed in either composition or metabolic characteristics of any major neutral lipid or phospholipid class in successive subcultures or following transformation. The overall lipid composition of the hamster astrocyte cultures closely resembled that of newborn hamster brain, but the phospholipid composition showed substantial differences. The cells contained as a percent of lipid P relatively more ethanolamine plasmalogen, choline plasmalogen and sphingomyelin and somewhat less phosphatidylcholine and phosphatidylethanolamine. The phospholipids of the hamster astrocyte and C6 cells were similar. Of the lipid precursors examined, [U-¹⁴C]glucose was incorporated best into all preparations. C6 glioma cells incorporated both [U-¹⁴C]glucose and [1-¹⁴C]acetate most actively. From 69–88% of ³²P incorporated into hamster astrocyte phospholipids was present in choline phosphoglycerides, whereas the corresonding figure for hamster brain dispersions was 53%. The ratio of specific activities of phosphatidylcholine to phosphatidylinositol was substantially higher in the cultured cells than in the brain preparations. The small pool of choline plasmalogen in the hamster astrocytes usually achieved the highest specific activity of any phospholipid. When [U-¹⁴C]glucose and [1-¹⁴C]acetate were precursors, the bulk of label in the astrocytes appeared in choline phosphoglycerides and triacyglycerol. Our results indicate that the hamster astrocyte cell line as grown expresses distinctive features of lipid composition and metabolism which are nearly constant through many generations.     

Lipid composition and metabolism in testicular and ejaculated ram spermatozoa

1. Spermatozoa collected directly from the testis of the conscious ram contain 25% more phospholipid than ejaculated spermatozoa. The concentration of lecithin, phosphatidylethanolamine and ethanolamine plasmalogen was greater in testicular spermatozoa; little difference was observed in choline plasmalogen. Both types of spermatozoa had significant amounts of cardiolipin and alkyl ether phospholipid. 2. The fatty acids in the phospholipid extracted from testicular spermatozoa have a very high content of palmitic acid. The phospholipids of ejaculated spermatozoa contained less palmitic acid, but more myristic acid. 3. Ejaculated spermatozoa contained less acyl ester and cholesterol. It is suggested that lipids are a source of substrate for spermatozoa during their passage through the epididymis. 4. Testicular spermatozoa when incubated with [U-¹⁴C]glucose incorporated more radioactivity into the glycerol part of the phospholipid and neutral lipid fractions than did ejaculated cells. The distribution of radioactivity in the individual phospholipids and neutral lipids was similar for both cell types. No radioactivity was detected in choline plasmalogen, which accounted for approx. 40% of the total phospholipid. 5. Testicular spermatozoa incorporated more radioactivity from glucose into formate than into acetate, whereas a higher proportion of radioactivity was found in acetate in ejaculated cells. 6. The implications of these lipid changes in the process of spermatozoal maturation are discussed.     

Skeletal muscle lipids. II. Changes in phospholipid composition in man from fetal to middle age

Phospholipid compositions were determined in samples of gastrocnemius muscles of individuals from fetal stage to the age of 55 yr. The lipids were separated by thin-layer chromatography. In order to enable characterization of the individual phospholipids, a lipid extract was prepared from pooled samples of gastrocnemius muscles from adult males and separated by ion-exchange chromatography on TEAE-cellulose. The individual phosphoglycerides were purified by thin-layer chromatography and then characterized according to their content of fatty acids, aldehydes, phosphorus, and the identity of the bases. The relative amounts of the major phospholipids, choline and ethanolamine phosphoglycerides, changed little with age, and in adult males they constituted 47% and 24%, respectively. Cardiolipin increased from 3% in the fetal stage to 9% by the end of the first year of life. Sphingomyelin and serine phosphoglyceride decreased with increasing age, while inositol phosphoglyceride increased. In adult males, cardiolipin constituted 10% of total lipid phosphorus, inositol phosphoglyceride constituted 9%, serine phosphoglyceride 3%, and sphingomyelin 7%.     

Axonal transport of phospholipids in rat visual system.

Abstract— Seventeen day old rats were injected intraocularly with a phospholipid precursor, [³²P]phosphate, and a glycoprotein precursor, [³H]fucose. Animals were killed between 1 h and 21 days later, and structures of the visual pathway (retina, optic nerve, optic tract, lateral geniculate body, and superior colliculus) were dissected. Radioactivity in phospholipids ([³²P] in solvent-extracted material) and in glycoproteins ([³H] in solvent-extracted residue) was determined. Incorporation of [³H]fucose into retinal glycoproteins peaked at 6–8 h. Labelled glycoproteins were present in superior colliculus by 2h after injection, indicating a rapid rate of transport; maximal labelling was at 8–10 h after injection. Incorporation of [³²P]phosphate into retinal phospholipids peaked at 1 day after injection. Phospholipids were also rapidly transported since label was present in the superior colliculus by 3 h after injection: however, maximal labelling did not occur until 5–6 days. These results indicate that newly synthesized phospholipids enter a preexisting pool, part of which is later committed to transport at a rapid rate. Transported phospholipids were catabolized at the nerve endings with a maximum half-life of several days; there was minimal recycling of precursor label. Lipids were fractionated by thin-layer chromatography, and radioactivity in individual phospholipid classes determined. Choline and ethanolamine phosphoglycerides were the major transported phospholipids, together accounting for approx 85% of the total transported lipid radioactivity. At early time points, the ratio of radioactivity in choline phosphoglycerides to that in ethanolamine phosphoglycerides increased in structures progressively removed from the site of synthesis (retina) but by 2 days approached a constant value. In each structure, choline phosphoglyceride-ethanolamine phosphoglyceride radioactivity ratios decreased with time, rapidly at first, but plateaued by 2 days. These results indicate that choline phosphoglycerides are committed to transport sooner than ethanolamine phosphoglycerides. Some experiments were also conducted using [2-³H]glycerol as a phospholipid precursor. Results concerning incorporation of this precursor into individual phospholipid classes and their subsequent axonal transport were comparable to those obtained using [³²P]phosphate, with the following exceptions: (a) incorporation of [2-³H]glycerol into retinal phospholipids was relatively rapid (near-maximal levels at 1 h after injection) although transport to the superior colliculus showed an extended time course very similar to [³²P]-labelled lipids; (b) [2-³H]glycerol was somewhat less efficient than [³²P]phosphate in labelling lipids committed to transport relative to labelling those which remained in the retina; and (c) [2-³H]glycerol did not label plasmalogens.     

Metabolism of triacylglycerol in developing rat brain

Metabolism of triacylglycerol (TAG) in developing brain has been examined. TAG is a relatively minor fraction of brain lipid in both suckling and adult rats and cannot be accounted for as entrapped blood. When glycerol tri[1-¹⁴C]oleate and [2-³H]glycerol trioleate were simultaneously injected intracerebrally into suckling rats, both labels appeared in diacylglycerol and the major phospholipids; acyl chain label was incorporated more extensively at early time points, with choline phosphoglycerides being most actively labeled. With [1-¹⁴C]fatty acids and [2-³H] glycerol administration, the specific activity of TAG was much greater than that of the more abundant phospholipids. Although direct acyl exchange between TAG and phospholipids was not demonstrated, relationships of TAG to selective mechanisms of phosphoglyceride synthesis were indicated.Abbreviations used TAG triacylglycerol - DAG diacylcerol - HPLC high performance liquid chromatography - CoA coenzyme A - BSA bovine serum albumin - TLC thin layer chromatography - DPM disintegrations per minute - ATP adenosine triphosphate - GLC gas liquid chromatography - PC choline, phosphoglyceride - PE ethanolamine phosphoglyceride - PS serine phosphoglyceride - PI inositol phosphoglyceride     

Serine and ethanolamine incorporation into different plasmalogen pools: Subcellular analyses of phosphoglyceride synthesis in cultured glioma cells

In cultured glioma cells, plasma membrane (PM) is enriched in phosphatidylserine (PtdSer) and plasmalogens (1-O-alk-1-enyl-2-acyl-sn-glycero-3-phosphoethanolamine). Serine can be a precursor of headgroups of both ptdSer and ethanolamine phosphoglycerides (PE) including plasmalogens and non-plasmalogen PE (NP-PE). Synthesis of phospholipids was investigated at the subcellular level using established fractionation procedures and incorporation of [³H(G)]L-serine and [1,2-¹⁴C]ethanolamine. Specific radioactivity of PtdSer from [³H]serine was 2-fold greater in PM than in microsomes, reaching maximum by 2–4 h. Labeled plasmalogen from [³H]serine appeared in PM by 4 h and increased to 48 h, whereas almost no plasmalogen accumulated in microsomes within 12 h. In contrast, labeled plasmalogen from [1,2-¹⁴C]ethanolamine appeared in both PM and microsomes at early incubation times and became enriched in PM beyond 12 h. Thus, in glioma cells: (1) greater and faster accumulation of labeled PtdSer in PM may reflect direct synthesis from serine within PM; (2) PM is a major source of PtdSer for decarboxylation and PE synthesis; (3) NP-PE in both PM and microsome provides headgroup for synthesis of plasmalogen; and, (4) plasmalogen synthesis may involve different intracellular pools depending on headgroup origin.Abbreviations NP-PE nonplasmenylethanolamine phosphoglycerides including both diacyl and alkylacyl species - PE total ethanolamine phosphoglycerides: plasmalogen-plasmenylethanolamine or alkenylacyl ethanolamine phosphoglyceride (1-O-alk-1-enyl-2-acyl-sn-glycero-3-phosphoethanolamine) - PL phospholipid - PM plasma membrane - PtdCho phosphatidylcholine - PtdSer phosphatidylserine     

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.     

Phosphatidohydrolase and base-exchange activity of commercial phospholipase D

Base-exchange activity was contrasted to the usual phosphatidohydrolase activity of commercial phospholipase D preparation from cabbage. The former activity was assayed by measuring the incorporation of labeled ethanolamine and choline into phospholipids. The latter activity was assayed by measuring the formation of phosphatidic acid with radioactive phosphatidylcholine microdispersion as substrate. The pH optimum for the base-exchange activity was about 9.0, whereas the phosphatidohydrolase activity had a pH optimum around 5.6. The incorporation of ethanolamine and choline into phospholipid was dependent upon the amount of acceptor asolectin microdispersion present. The optimum concentration of Ca²⁺ in the base-exchange reaction was about 4 mm, whereas the optimum concentration for the phosphatidohydrolase activity was greater than 28 mm. The incorporation of ethanolamine into phospholipid was decreased 50% by heating the enzyme preparation at 50°C for about 10 min, whereas the choline incorporation decreased approximately 20% and the phosphatidohydrolase activity decreased by about 10% under these conditions.Hemicholinium-3 was found to be a noncompetitive inhibitor for the incorporation of both ethanolamine and choline into phospholipid with respective K_i, values of 1.25 × 10^?3 and 2.50 × 10^?3m. The K_m values for ethanolamine and choline in the base-exchange reaction were 1.25 × 10^?3 and 2.50 × 10^?3m, respectively. The apparent K_m for phosphatidylcholine for the phosphatidohydrolase activity was about 1.5 × 10^?3m, and there was no inhibition by hemicholinium-3.     

Phospholipid composition of dystrophic chicken erythrocyte plasmalemmae II. Characterization of a unique lipid from dystrophic erythrocyte membranes as ethanolamine plasmalogen

The phospholipid content of normal (line 412) and dystrophic (line 413) chicken erythrocyte plasmalemmae has been quantified on a developmental basis using sex matched controls. A specific minor phospholipid component, ethanolamine plasmalogen, is identified from dystrophic erythrocyte membrane preparations. To arrive at this identification, data from studies utilizing gas-liquid chromatography, thin-layer chromatography, [¹⁴C]ethanolamine incorporation, and biochemical assay for specific organic moieties were correlated. This phospholipid has the potential to alter and regulate membrane fluidity and thus membrane function. The possible presence of significant concentrations of plasmalogen in human dystrophic tissues may serve as a marker for dystrophy and thus be of clinical importance.     

Structure and dynamics of plasmalogen model membranes containing cholesterol: a deuterium NMR study

Deuterium nuclear magnetic resonance (²H-NMR) was used to investigate the structure and dynamics of the sn-2 hydrocarbon chain of semi-synthetical choline and ethanolamine plasmalogens in bilayers containing 0, 30, and 50 mol% cholesterol. The deuterium NMR spectra of the choline plasmalogen yielded well-resolved quadrupolar splittings which could be assigned to the corresponding hydrocarbon chain deuterons. The sn-2 acyl chain was found to adopt a similar conformation as observed in the corresponding diacyl phospholipid, however, the flexibility at the level of the C-2 methylene segment of the plasmalogen was increased. Deuterium NMR spectra of bilayers composed of the ethanolamine plasmalogen yielded quadrupolar splittings of the C-2 segment much larger than those of the corresponding diacyl lipids, suggesting that the sn-2 chain is oriented perpendicular to the membrane surface at all segments. Cholesterol increased the ordering of the choline plasmalogen acyl chain to the same extent as in diacyl lipid bilayers. T₁ relaxation time measurements demonstrated only minor dynamical differences between choline plasmalogen and diacyl lipids in model membranes.     

Phospholipid synthesis in aging potato tuber tissue

The effect of activation (“aging”) of potato tuber slices on their phospholipid metabolism was investigated. Aged slices were incubated with ¹⁴C labeled choline, ethanolamine, methionine, serine, and acetate. In all cases, the incorporation of radioactivity into the lipid fraction increased with the length of time the slices were aged. This incorporation was shown to be true synthesis and not exchange between precursors and existing phospholipids.

The increased incorporation of labeled choline into lipids was mainly due to an increase in its uptake by the tissue, the presence of actidione during aging prevented this increased uptake. The increase in the incorporation of labeled acetate into lipids resulted from the development of a fatty acid synthetase during aging. In the case of ethanolamine, both its uptake into the tissue and its incorporation into the lipid fraction increased.

The phospholipids formed from these precursors were identified by paper and thin-layer chromatography. The major compound formed from choline was lecithin, while phosphatidylethanolamine and a small amount of lecithin were formed from ethanolamine.

     

Cerebral microvascular and parenchymal phospholipid composition in the mouse

Cerebral microvessels consisting predominantly of capillaries and small arterioles (<30 m dia.) were isolated from the cerebral cortex and cerebellum of 3-month-old mice. Lipids were extracted from both microvascular and brain parenchymal fractions and the major phospholipid classes (choline phosphoglyceride, ethanolamine phosphoglyceride, inositol phosphoglyceride, serine phosphoglyceride, and sphingomyelin) separated by 2-dimensional TLC. Comparison of mol % determined by phosphate analysis of each phospholipid revealed significant differences in membrane composition of ethanolamine phosphoglyceride, inositol phosphoglyceride, and sphingomyelin between microvascular and parenchymal components of the central nervous system. Moreover, the choline phosphoglyceride/sphingomyelin mol ratio, one of three determinants of membrane fluidity, is significantly lower for microvessel membrane than for membranes of the brain parenchyma.     

Peripheral Nerve Phospholipid Composition: Development in Normal Nerve and Age-Dependent Changes in Wallerian Degenerated Nerve

Abstract: The phospholipid composition of normal peripheral nerve as a function of developmental age as well as that of Wallerian-degenerated nerve as a function of age at nerve transection and duration of Wallerian degeneration have been quantitated in rabbit sciatic nerve. During development, increases in the proportions of ethanolamine plasmalogen, sphingomyelin, and combined phosphatidyl serine plus phosphatidyl inositol and decreases in the proportions of phosphatidyl choline and phosphatidyl ethanolamine correlated well with the concurrent myelin accretion. During Wallerian degeneration, age-dependent changes in phospholipid composition were observed. The large and statistically significant increase in the proportion of phosphatidyl choline and decrease in the proportion of ethanolamine plasmalogen were manifest promptly in nerves transected at 2 weeks of age but in a delayed manner in nerves transected at 8, 12, and 20 weeks of age. The rate of loss of individual phospholipids was greater in nerves transected at younger ages. The findings from normal developing peripheral nerve may well serve as baseline data for subsequent studies of phospholipid composition in pathological peripheral nerve. The Findings from Wallerian-degenerated peripheral nerve provide additional evidence for age-dependent chemical changes occurring in Wallerian-degenerated peripheral nerve that may be of significance in explaining the superior functional recovery from peripheral nerve injury observed in younger compared with older subjects.     

Permeability properties of unilamellar vesicles containing choline plasmalogens and comparison with other choline glycerophospholipid species

The rates of non-electrolyte and ion diffusion across bilayer membranes consisting of choline plasmologens or of their alkyl and acyl analogs were studied. The influx of [¹⁴C]glucose, ⁸⁶Rb⁺ and ³⁶Cl^? into small unilamellar vesicles made from a semisynthetic choline plasmalogen and from synthetic diacyl, alkylacyl and dialkyl analogs with comparable side chain compositions were measured. Rates of glucose and Rb⁺ diffusion are about equal in alkenylacyl- and diacyl-glycerophosphocholine (GPC) bilayers, but are reduced in dialkyl-GPC membranes; the permeability coefficients correlate with the packing densities of the respective choline glycerophospholipids in monolayers at the air water interface. Rates of chloride diffusion are consistently higher in membranes formed from phospholipids containing alkenyl or alkyl other bonds as compared to the diacyl analogs. Highest rates of Cl^? diffusion are observed with choline plasmalogen vesicles. The phospholipid side chain composition has little influence on Cl^? permeation, but glucose and Rb⁺ diffusion are markedly affected. Incorporation of cholesterol (30 mol%) into choline plasmalogen membranes reduces their solute permeability by approximately 70%. A similar effect is found with the other choline phospholipid analogs. Thus, the choline phospholipid—cholesterol interaction, as far as it is reflected in reduced bilayer permeability, is not influenced by the presence of the alkenylether bond of plasmalogens.     

Separation and analysis of P-labeled phospholipids by a simple and rapid thin-layer chromatographic procedure and its application to cultured neuroblastoma cells

A two-directional thin-layer chromatographic method for the rapid analysis of phospholipids from cultured cells is described. The procedure permits reliable separation of the common and minor phospholipid species using regular silica gel G chromatoplates. It is based primarily on the shortening of the running distances of the developing solvents and the use of suitable solvent systems. The method has been used to study changes in the patterns of ³²P-labeled phospholipids in cultured cells under a variety of growth conditions. It is shown that, in the presence of -propranolol, incorporation of ³²P into choline and ethanolamine phospholipids is markedly reduced, whereas an increase of label in phosphatidylglycerol is observed. The latter may serve as a precursor for lysobisphosphatidic acid formation. Following treatment of cells with dimethylaminoethanol, a high proportion of label is incorporated into dimethylethanolamine phosphoglycerides.     

Metabolism of phospholipids by spermatozoa and seminal plasma

1. The hydrolysis of added (32)P-labelled phospholipids by whole ram and bull semen and the separated spermatozoal and plasma components was examined. 2. The ethanolamine phosphoglycerides were rapidly attacked by washed spermatozoa, forming predominantly glycerylphosphorylethanolamine, but with whole semen and seminal plasma a lysophosphatidylethanolamine was also detected. 3. The hydrolysis of lecithin by spermatozoa and plasma was very slow, and glycerylphosphorylcholine was the sole product detected. 4. Ram testicular spermatozoa were comparatively inactive in metabolizing both phospholipids, but ampulla contents showed the same activity as ejaculated semen. 5. Phosphatidylinositol was metabolized by spermatozoa obtained from any portion of the ram reproductive tract and also by seminal plasma. With testicular components, ampulla contents and washed ejaculated spermatozoa, inositol monophosphate, an unidentified phosphate ester and inorganic phosphate were the main products. In contrast, with whole semen and seminal plasma, glycerylphosphorylinositol was the predominant water-soluble phosphate ester. 6. Accessory-gland secretion obtained from vasectomized rams showed a pronounced phospholipase A activity towards ethanolamine phosphoglyceride. 7. On aerobic incubation of whole ram semen there was a decrease in the concentration of all phospholipid classes, although cardiolipin showed the greatest percentage decrease. In the choline phosphoglyceride fraction, this loss was confined to the plasmalogen component. This breakdown of phospholipids was decreased considerably when the spermatozoa were washed, and was not observed when whole bull semen was incubated under similar conditions.     

Modification of glycerolipid metabolism in L-M fibroblasts by an unnatural amino-alcohol, N-isopropylethanolamine.

The unnatural amino-alcohol, N-isopropylethanolamine, is incorporated into a phospholipid by monolayers of L-M fibroblasts. This phospholipid was identified as 1,2-diacyl-$\text{sn}$-glycero-3-phosphoisopropylethanolamine by using chemical and enzymatic procedures combined with thin-layer and gas-liquid chromatography. Since the phospho-N-isopropylethanolamine moiety is removed by phospholipase C, the stereochemistry of the phospholipid analog is identical to naturally occurring phosphoglycerides. Incubation of cells in 10 mM N-isopropylethanolamine inhibited the incorporation of [¹⁴C]choline and [¹⁴C]ethanolamine into phospholipids and stimulated the incorporation of [1-¹⁴C]palmitic acid and [1-¹⁴C]hexadecanol into triacylglycerols and alkyldiacylglycerols. These results indicate that N-isopropylethanolamine affects glycerolipid synthesis at the diradylglycerol branch point.     

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.