Effect of a phosphonic acid analog of choline phosphate on phospholipid metabolism in Tetrahymena

When Tetrahymena thermophila is grown on a medium containing increasing concentrations of N,N,N-trimethyl-2-aminoethylphosphonate (TMAEP), up to 60% of the choline phosphate in phosphatidylcholine is replaced by the phosphonic acid. There is an increase in the relative amount of quaternary ammonium-containing lipid (phosphatidylcholine plus TMAEP-lipid) at the expense of phosphatidylethanolamine. There is no effect of the TMAEP on either 2-aminoethylphosphonolipid levels or on de novo 2-aminoethylphosphonate synthesis. Higher levels of TMAEP in the medium (25 and 50 mm) lead to decreased growth of Tetrahymena and to an abnormal cell morphology.     

Catabolism and Detoxification of 1-Aminoalkylphosphonic Acids: N-Acetylation by the phnO Gene Product

In Escherichia coli uptake and catabolism of organophosphonates are governed by the phnCDEFGHIJKLMNOP operon. The phnO cistron is shown to encode aminoalkylphosphonate N-acetyltransferase, which utilizes acetylcoenzyme A as acetyl donor and aminomethylphosphonate, (S)- and (R)-1-aminoethylphosphonate, 2-aminoethyl- and 3-aminopropylphosphonate as acetyl acceptors. Aminomethylphosphonate, (S)-1-aminoethylphosphonate, 2-aminoethyl- and 3-aminopropylphosphonate are used as phosphate source by E. coli phn⁺ strains. 2-Aminoethyl- or 3-aminopropylphosphonate but not aminomethylphosphonate or (S)-1-aminoethylphosphonate is used as phosphate source by phnO strains. Neither phn⁺ nor phnO strains can use (R)-1-aminoethylphosphonate as phosphate source. Utilization of aminomethylphosphonate or (S)-1-aminoethylphosphonate requires the expression of phnO. In the absence of phnO-expression (S)-1-aminoethylphosphonate is bacteriocidal and rescue of phnO strains requires the simultaneous addition of d-alanine and phosphate. An intermediate of the carbon-phosphorus lyase pathway, 5′-phospho-α-d-ribosyl 1′-(2-N-acetamidoethylphosphonate), a substrate for carbon-phosphorus lyase, was found to accumulate in cultures of a phnP mutant strain. The data show that the physiological role of N-acetylation by phnO-specified aminoalkylphosphonate N-acetyltransferase is to detoxify (S)-1-aminoethylphosphonate, an analog of d-alanine, and to prepare (S)-1-aminoethylphosphonate and aminomethylphosphonate for utilization of the phosphorus-containing moiety.     

The effects of high concentrations of sodium or calcium ions on the lipid composition and properties of Tetrahymena membranes

Tetrahymena pyriformis cells have been grown in media varying in NaCl concentration from 3.7 mM (normal medium) to 0.3 M and varying in CaCl₂ from 0.2 mM (normal medium) to 0.1 M. Tetrahymena grown in 0.3 M NaCl showed relatively few alterations in phospholipid composition, with significant changes being found only in the cell surface membranes (pellicle), which increased in phosphatidylethanolamine content from 39% (low Na⁺) to 48% (high Na⁺) of the total phospholipids. The small decrease in fatty acid unsaturation and increase in shorter chain fatty acids in pellicle phospholipids were not statistically significant. No significant changes in phospholipid head group composition or fatty acid distribution were observed in high Ca²⁺-grown cells. Complementary studies of membrane fluidity, as inferred from freeze-fracture electron microscopy analysis, indicated that membranes of high Na⁺-acclimated cells were similar to those of control cells, when each was measured in its respective medium. However, the outer alveolar membrane of the pellicle and the food vacuolar membrane were considerably less fluid in high-Ca²⁺ cells. The lower fluidity in vacuolar membranes may have been responsible for alterations in the cells' capacity to form food vacuoles.     

The role of serine in the lipid metabolism of the rat tapeworm Hymenolepisdiminuta

Webb R. A. and Mettrick D. F. 1973. The role of serine in the lipid metabolism of the rat tapeworm Hymenolepis diminuta. International Journal for Parasitology3: 47–58. The inter-relationship between the amino acid serine and lipid metabolism in the rat tapeworm Hymenolepis diminuta has been studied under in vitro conditions. The label from U-¹⁴C-serine, U-¹⁴C-glucose and 1-¹⁴C-oleic acid was rapidly incorporated into worm tissue phospho- and glycolipids, the latter illustrating the synthesis of cerebrosides by H. diminuta. Activity from U-¹⁴C-serine was recovered in phosphatidylserine, phosphatidylethanolamine, cerebrosides and several unidentified lipid-like compounds. The majority of the label recovered in phosphatidylethanolamine was associated with the ethanolamine moiety; in the cerebrosides with the sphingosine moiety. The sugar moiety of the cerebrosides was galactose.Pulse label studies showed a serine flux phenomenon, and a rapid rate of turnover of some of the unidentified compounds.Exogenous ethanolamine had no detectable effect upon absorption and conversion of serine to tissue phosphatidylethanolamine. Incubation of H. diminuta homogenates with phosphatidyl U-¹⁴C-serine resulted in the recovery of considerable activity in phosphatidylethanolamine. The results show that the major pathway of phosphatidylethanolamine synthesis is by decarboxylation of phosphatidylserine.     

Asymmetric synthesis followed by transmembrane movement of phosphatidylethanolamine in rat liver endoplasmic reticulum

Studies with phospholipase C have indicated that two-thirds of the phosphatidylethanolamine of rat liver endoplasmic reticulum is located in the inner leaflet of the membrane bilayer. Phosphatidyl[¹⁴C]ethanolamine is synthesised in microsomes incubated with CDP[¹⁴C]ethanolamine. Using phospholipase C as a probe we have observed that the labelled phospholipid is initially (1–2 min) concentrated in the ‘outer leaflet’ of the membrane bilayer. The specific activity of this pool of phosphatidylethanolamine was 3.5 times that of the inner leaflet. If, however, the microsomes were opened with 0.4% taurocholate or the French pressure cell to make both sides of the bilayer available to phospholipase C, the phosphatidylethanolamine behaves as a single pool for hydrolysis. On longer incubation, up to 30 min, with CDP[¹⁴C]ethanolamine the specific activity of the outer leaflet phosphatidylethanolamine becomes close to that of the inner leaflet. In chase experiments, in which microsomal phosphatidylethanolamine was labelled by incubation with CDP[¹⁴C]ethanolamine for 1 min, the reaction stopped by addition of calcium, and the microsomes isolated by centrifugation and reincubated, labelled phosphatidylethanolamine was transferred from the ‘outer leaflet’ to the ‘inner leaflet’, so that both were equally labelled. These observations suggest that phosphatidylethanolamine is synthesised at the cytoplasmic leaflet of the endoplasmic reticulum and subsequently transferred across the membrane to the cisternal leaflet of the bilayer. Transmembrane movement is apparently temperature-dependent and independent of continued synthesis of phosphatidylethanolamine.     

The effect of phosphate deficiency on membrane phospholipid composition of bean (Phaseolus vulgaris L.) roots

Plasma membranes were isolated from roots of bean (Phaseolus vulgaris L.) plants cultured on phosphate sufficient or phosphate deficient medium. The phospholipid composition of plasma membranes was analyzed and compared with that of the microsomal fraction. Phosphate deficiency had no influence on lipid/protein ratio in microsomal as well as plasma membrane fraction. In phosphate deficient roots phospholipid content was lower in the plasma membrane, but did not change in the microsomal fraction. Phosphatidylcholine and phosphatidylethanolamine were two major phospholipids in plasmalemma and microsomal membranes (80 % of the total). After two weeks of phosphate starvation a considerable decrease (about 50 %) in phosphatidylcholine and phosphatidylethanolamine in microsomal membranes was observed. The decline in two major phospholipids was accompanied by an increase in phosphatidic acid and lysophosphatidylcholine content. The effect of alterations in plasma membrane phospholipids on membrane function e.g. nitrate uptake is discussed.     

Phosphatidylethanolamine synthesized by four different pathways is supplied to the plasma membrane of the yeast Saccharomyces cerevisiae

In this study, we examined the contribution of the four different pathways of phosphatidylethanolamine (PE) synthesis in the yeast Saccharomyces cerevisiae to the supply of this phospholipid to the plasma membrane. These pathways of PE formation are decarboxylation of phosphatidylserine (PS) by (i) phosphatidylserine decarboxylase 1 (Psd1p) in mitochondria and (ii) phosphatidylserine decarboxylase 2 (Psd2p) in a Golgi/vacuolar compartment, (iii) incorporation of exogenous ethanolamine and ethanolamine phosphate derived from sphingolipid catabolism via the CDP-ethanolamine pathway in the endoplasmic reticulum (ER), and (iv) synthesis of PE through acylation of lyso-PE catalyzed by the acyl-CoA-dependent acyltransferase Ale1p in the mitochondria associated endoplasmic reticulum membrane (MAM). Deletion of PSD1 and/or PSD2 led to depletion of total cellular and plasma membrane PE level, whereas mutation in the other pathways had practically no effect. Analysis of wild type and mutants, however, revealed that all four routes of PE synthesis contributed not only to PE formation but also to the supply of PE to the plasma membrane. Pulse-chase labeling experiments with L[³H(G)]serine and [¹⁴C]ethanolamine confirmed the latter finding. Fatty acid profiling demonstrated a rather balanced incorporation of PE species into the plasma membrane irrespective of mutations suggesting that all four pathways of PE synthesis provide at least a basic portion of “correct” PE species required for plasma membrane biogenesis. In summary, the PE level in the plasma membrane is strongly influenced by total cellular PE synthesis, but fine tuned by selective assembly mechanisms.     

Phase behavior of the major lipids of Tetrahymena ciliary membranes

The major lipids of Tetrahymena membranes have been purified by thin-layer and high pressure liquid chromatography and the phosphatidylethanolamine and aminoethylphosphonate lipids were examined in detail. ³¹P-NMR, X-ray diffraction and freeze-fracture electron microscopy were employed to describe the phase behavior of these lipids. The phosphatidylethanolamine was found to form a hexagonal phase above 10°C. The aminoethylphosphonate formed a lamellar phase up to 20°C, but converted to a hexagonal phase structure at 40°C. Small amounts of phosphatidylcholine stabilized the lamellar phase for the aminoethylphosphonate. ³¹P-NMR spectra of the intact ciliary membranes were consistent with a phospholipid bilayer at 30°C, suggesting that phosphatidylcholine in the membrane stabilized the lamellar form, even though most of the lipid of that membrane prefers a hexagonal phase in pure form at 30°C. ³¹P-NMR spectra also showed a distinctive difference in the chemical shift tensor of the aminoethylphosphonolipid, when compared to that of phosphatidylethanolamine, due to the difference in chemical structure of the polar headgroups of the two lipids.     

Phosphatidylcholine homeostasis in phosphatidylethanolamine-depleted Tetrahymena

The relative contributions of the two pathways of phosphatidylcholine biosynthesis, phosphatidylethanolamine N-methyltransferase (EC 2.1.1.17) and diacylglycerol: CDP-choline cholinephosphotransferase (EC 2.7.8.1), are altered in the ciliate protozoan Tetrahymena thermophila whose phospholipid composition has been modified by culturing the organism in the presence of one of several aminophosphonic acids, as determined by measuring the incorporation of [methyl-3H]choline and [methyl-14C]methionine into phosphatidylcholine in vivo. In control cells the phosphotransferase pathway provides about 40% of the phosphatidylcholine, while in cells grown with 2-aminoethylphosphonate (AEP), 3-aminopropylphosphonate (APP), and N,N,N-trimethylaminoethyl-phosphonate (TMAEP) the contribution of the phosphotransferase pathway to phosphatidylcholine formation is 75, 90, and 26%, respectively. In AEP- and APP-grown cells, in which 80% of the phosphatidylethanolamine has been replaced by the corresponding phosphonolipid, the methyltransferase is less active since the level of the substrate phosphatidylethanolamine is reduced and neither of the phosphonolipids is a substrate for the enzyme. In TMAEP-grown cells, TMAEP competes with and reduces the incorporation of phosphocholine by the phosphotransferase pathway, leading to a smaller contribution of the pathway to phosphatidylcholine biosynthesis. The relative amounts of the two different radioactive labels incorporated into diacylphosphatidylcholine vs alkylacylphosphatidylcholine are also altered in the phosphonate-grown cells. The exogenous AEP induces a change in the glyceryl ether content of the 2-aminoethylphosphonolipid--33% in the AEP-grown cells compared to 70% in the control cells--indicating that the exogenous AEP is entering the phospholipids by the ethanolamine-phosphotransferase pathway rather than by the route of the endogenous AEP.     

Differential Utilization of the Ethanolamine Moiety of Phosphatidylethanolamine Derived from Serine and Ethanolamine during NGF-Induced Neuritogenesis of PC12 Cells

Neurite elongation involves the expansion of the plasma membrane and phospholipid synthesis. We investigated membrane phosphatidylethanolamine (PE) biosynthesis in PC12 cells during neurite outgrowth induced by nerve growth factor (NGF). When PE was prelabeled with [³H]ethanolamine and the radioactivity was chased by incubation with 1 mM unlabeled ethanolamine, the radioactivity of [³H]PE steadily declined and [³H]ethanolamine was released into the medium in NGF-treated cells during neurite outgrowth; in the absence of unlabeled ethanolamine, the radioactivity of [³H]PE remained relatively constant for at least 24 hr. In undifferentiated cells but not in NGF-treated cells, [³H]phosphoethanolamine accumulated in significant amounts during pulse labeling, and was converted partly to PE but largely released into the medium irrespective of incubation with unlabeled ethanolamine. The decline in the radioactivity of [³H]PE and release of [³H]ethanolamine following incubation with unlabeled ethanolamine were also observed in undifferentiated cells. Thus, the ethanolamine moiety of PE derived from ethanolamine is actively recycled in both differentiated and undifferentiated cells. When PE was derived from [³H]serine through phosphatidylserine (PS) decarboxylation, the decrease in radioactivity of [³H]PE and release of [³H]ethanolamine into the medium following incubation with unlabeled ethanolamine were observed only in NGF-treated cells, but not in undifferentiated cells, indicating that the ethanolamine moiety of PE derived from PS is actively recycled only in the cells undergoing NGF-induced neuritogenesis. Thus, in PC12 cells, the ethanolamine moiety of PE derived from PS is regulated differently from that of PE derived from ethanolamine.     

Interactions of phosphorylethanolamine analogs with phosphorylethanolamine-citidylyltransferase]

Kinetic studies of ethanolaminephosphate-cytidylyltransferase (E.C. 2.7.7.14) from rat liver have been carried out in presence of structural analogues of ethanolaminephosphate : these compounds acted as inhibitors of the enzyme: - 2-aminoethylphosphonate behaved as a substrate and a competitive inhibitor to phosphorylethanolamine: the Km value of 2-aminoethylphosphonate was nearly the same as its Ki value, at pH = 5,5 (30 X 10(-3) M and 24 x 10(-3) M, respectively). - 3-aminopropylphosphonate was also a competitive inhibitor. It appeared to be the best inhibitor at pH optimum (pH = 7,7). - 1-aminoethylphosphonate behaved as a noncompetitive inhibitor. However, cytidylyltransferase was relatively specific, inhibitions being always weak. Inhibitory power of phosphonates was stimulated by Mg++.     

Specific induction of TaAAPT1, an ER- and Golgi-localized ECPT-type aminoalcoholphosphotransferase, results in preferential accumulation of the phosphatidylethanolamine membrane phospholipid during cold acclimation in wheat

Cold acclimation requires substantial alteration in membrane property. In contrast to well-documented fatty acid unsaturation during cold acclimation, changes in phospholipid biosynthesis during cold acclimation are less understood. Here, we isolated and characterized two aminoalcoholphosphotransferase (AAPT) cDNAs, TaAAPT1 and TaAAPT2, from wheat. AAPTs utilize diacylglycerols and CDP-choline/ethanolamine as substrates and catalyze the final step of the CDP-choline/ethanolamine pathway for phosphatidylcholine (PC)/phosphatidylethanolamine (PE) synthesis, respectively. Functionality of TaAAPT1 and TaAAPT2 was demonstrated by heterologous expression in a yeast cpt1Δ ept1Δ double mutant that lacks both AAPT activities. Detailed characterization of AAPT activities from the transformed mutant cells indicated that TaAAPT1 is an ECPT-type enzyme with higher ethanolamine phosphotransferase (EPT) activity than choline phosphotransferase (CPT) activity, while TaAAPT2 is a CEPT-type with the opposite substrate preference. Transient expression of GFP-fused TaAAPT1 and TaAAPT2 proteins in wheat and onion cells indicated they are localized to both the endoplasmic reticulum and Golgi apparatus, suggesting that the final synthesis of PE and PC via the CDP-choline/ethanolamine pathway occurs in these organella. Quantitative PCR analyses revealed that TaAAPT1 expression is strongly induced by cold, while TaAAPT2 was constitutively expressed at lower levels. Measurement of phospholipid content in wheat leaves indicated that PE is more prominently increased in response to cold than PC and accordingly PE/PC ratio increased from 0.385 to 0.530 during 14 days of cold acclimation. Together, these data suggested that an increase in the PE/PC ratio during cold acclimation is regulated at the final step of the biosynthetic pathway.     

A phospholipid serine base exchange enzyme

A membrane bound L-serine exchange enzyme which catalyzes the exchange reaction between L-serine and phospholipid-base was solubilized and separated from the ethanolamine-exchange enzyme by Sepharose 4B and DEAE-cellulose column chromatography. The separated fraction was purified approximately 37-fold with a yield of 2--5%. This fraction did not possess ethanolamine or choline exchange activity. The optimal pH was approx. 8.0, the incorporation rate of L-serine into phospholipid was linear up to 20 min incubation time and the activity was maximum at 10 mM CaCl2. The calculated Km value for L-serine was 0.4 mM. Ethanolamine phospholipid was the most effective acceptor for L-serine incorporation, particularly ethanolamine plasmalogen. The Km values obtained were: 0.25 mM for ethanolamine plasmalogen, 0.25mM for pig liver phosphatidylethanolamine and 0.66 mM for egg yolk phosphatidylethanolamine. These observations suggest that the hydrophobic moiety in ethanolamine phospholipid, as well as the base moiety, is important for the affinity of the L-serine exchange enzyme. Neither ethanolamine nor choline inhibited the L-serine exchange activity. There was no detectable conversion of phosphatidylcholine or phosphatidylethanolamine to phosphatidic acid by the partially purified enzyme.     

Phosphatidylethanolamine biosynthesis in rat mammary carcinoma cells that require and do not require ethanolamine for proliferation

Epithelial cells and some of their transformed derivatives require ethanolamine to grow normally in defined culture medium. When these cells are cultured without ethanolamine, the amount of cellular phosphatidylethanolamine is considerably reduced. Using a set of rat mammary carcinoma cell lines whose growth is responsive (64-24 cells) and not responsive (22-1 cells) to ethanolamine, the biochemical mechanism of ethanolamine responsiveness was investigated. The biosynthesis and metabolism of phospholipid, particularly of those involving phosphatidylethanolamine, were thus compared between the two types of cells. The incorporation of [3H]serine into phosphatidylserine and phosphatidylethanolamine in 64-24 cells was 60 and 37%, respectively, of those in 22-1 cells. However, the activity of phosphatidylserine decarboxylase was virtually the same in these cell lines. When these cells were cultured in the presence of [32P]phosphatidylcholine and [32P]phosphatidylethanolamine, the rate of accumulation of 32P-labeled phosphatidylserine from the radioactive phosphatidylethanolamine was considerably reduced in 64-24 cells compared to that in 22-1 cells, although the rate of synthesis of phosphatidylserine and phosphatidylethanolamine from the radioactive phosphatidylcholine was similar between the two cell lines. The rate of labeling phosphatidylcholine from the radioactive phosphatidylethanolamine was also reduced in 64-24 cells, although the difference was not as great as that of phosphatidylserine. Incorporation of 32P into phosphatidylethanolamine was correlated with the concentration of ethanolamine in the culture medium in 64-24 cells, whereas in 22-1 cells the incorporation was not influenced by ethanolamine. Enzyme activities of the CDP-ethanolamine pathway were not significantly different between the two cell lines. The rate of degradation of phosphatidylethanolamine was also similar in these cell lines. These results show that ethanolamine responsiveness of 64-24 cells, and probably other epithelial cells, is due to a limited ability to synthesize phosphatidylserine resulting from a limited base-exchange activity utilizing phosphatidylethanolamine.     

The biosynthesis of phosphatidylcholine by methylation of phosphatidylethanolamine derived from ethanolamine is not required for lipoprotein secretion by cultured rat hepatocytes

The role that phosphatidylcholine biosynthesis plays in the assembly and secretion of lipoproteins has been investigated in rat hepatocytes, since phosphatidylcholine is the major phospholipid in all serum lipoproteins. Phosphatidylcholine in rat hepatocytes can be made via the CDPcholine pathway or by the methylation of phosphatidylethanolamine. A specific inhibitor of cellular transmethylation, 3-deazaadenosine (10 microM), has been incubated with rat hepatocytes, and we have shown that the biosynthesis of phosphatidylcholine via the methylation of phosphatidylethanolamine derived from ethanolamine was inhibited by greater than 95%. However, incubation of 3-deazaadenosine with cultured rat hepatocytes for up to 18 h did not affect the secretion of any of the apoproteins into VLDL, LDL, HDL fractions or a fraction with density greater than 1.18 g/ml (albumin was the major protein). Nor was there any effect by 3-deazaadenosine on the amount of phosphatidylcholine secreted into the culture medium or into VLDL or HDL. After 18 h the amount of phosphatidylethanolamine that accumulated in the cells was doubled by treatment with 3-deazaadenosine, and the amount of phosphatidylethanolamine secreted into the medium was increased by approximately 70%. It is thus apparent that the synthesis of phosphatidylcholine from ethanolamine is not required for lipoprotein secretion by rat hepatocytes.     

PHOSPHOLTPID METABOLISM IN ISOLATED NEURONAL AND GLIAL CELLS FROM BRAINS OF 17-DAY OLD RATS1

Neuronal and glial cells were isolated from the brains of 17-day old rats and incubated for 5 h with either radioactive inorganic phosphate, palmitate, serine, choline or ethanolamine in a tissue culture medium. A comparison of the results suggests that both neuronal and glial cells exhibit effective de novo, phospholipid synthesis and that the observed differences in the uptake are due more to quantitative rather than qualitative differences in phospholipid metabolism of both cell types. Incubations of the combined neuronal and glial fractions with ³²PO₄ and [³H]palmitate result in incorporations up to 100% higher than calculated from incubations of the separate fractions, suggesting that phospholipid metabolism of neuronal and glial cells may exhibit cooperativity.     

Effects of phosphoethanolamine and ethanolamine on growth of mammary carcinoma cells in culture

Phosphoethanolamine (PEtn) was previously shown to be a potent mitogen for a rat mammary carcinoma cell line, 64-24. The objective of this study was to elucidate the role of phosphoethanolamine as a mitogen. The growth stimulatory effect of various compounds related to PEtn was examined, and ethanolamine (Etn) and compounds whose structures resembled Etn were also found to be active. Among several neoplastic mammary epithelial cell lines of human and rat tested, a human line, T47-D, gave a positive growth response to phosphoethanolamine. The results suggest that a positive growth response to PEtn is correlated with growth response of a cell line to prolactin in culture. PEtn and Etn (10^?6 M) added to the medium incorporated efficiently into cellular phosphatidylethanolamine. After 3–4 days in culture more than 50% of the cellular phosphatidylethanolamine appeared to be derived from exogenous PEtn or Etn. Moreover, phosphatidylethanolamine content in phospholipid became three times higher than that without Etn in the medium.     

Biosynthesis of phosphatidylethanolamine via the CDP-ethanolamine route is an important pathway in isolated rat hepatocytes

In the present study pulse-label and pulse-chase experiments with isolated rat hepatocytes in suspension were designed to investigate the effects of the presence of either serine or ethanolamine in the medium on the rate of phosphatidylethanolamine synthesis via the CDPethanolamine pathway and by decarboxylation of phosphatidylserine. Addition of serine to the medium did not affect the incorporation of [1,2-14C]ethanolamine into phosphatidylethanolamine. Pulse-label experiments showed that the incorporation of [3H]serine into phosphatidylserine decreased in the presence of ethanolamine with a corresponding decrease of the incorporation of label into the ethanolamine base moiety of phosphatidylethanolamine. However, the radioactivity in the diacylglycerol part of phosphatidylethanolamine was considerably higher in the presence of ethanolamine than in its absence. Pulse-chase experiments with labelled serine demonstrated that the conversion of phosphatidylserine to phosphatidylethanolamine was not affected by varying concentrations of ethanolamine. Our observations indicate that in the presence of ethanolamine the biosynthesis of phosphatidylethanolamine via the CDPethanolamine pathway is enhanced relative to the synthesis by decarboxylation of phosphatidylserine.     

Characterization and comparison of lipids in different squid nervous tissues

We have studied the lipid composition of brain (optic and cerebral lobes), stellate ganglia and fin nerves of the squid. Cholesterol, phosphatidylethanolamine and phosphatidylcholine were the major lipids in these nervous tissues. Phosphatidylethanolamine contained about 3% of its amount in [corrected] plasmalogen form. Phosphatidylserine and -inositol, sphingomyelin and ceramide 2-aminoethylphosphonate were also present in significant amounts. In addition, cardiolipin and free fatty acids were detected in brain (each 2-3% of total lipids) and stellate ganglia (about 1% each), but not in fin nerves. Phosphatidylethanolamine, phosphatidylserine and phosphatidylinositol from brain contained large amounts of polyunsaturated fatty acids, namely 20:4, 20:5 and 22:6 in the n-3 family. On the other hand, phosphatidylcholine, cardiolipin, and sphingomyelin, and ceramide 2-aminoethylphosphonate contained only saturated or monounsaturated C16-C18 fatty acids. The aldehyde moieties of ethanolamine plasmalogen were also C16-C18 saturated or monounsaturated. These lipid compositions are compared with those in other invertebrate nervous systems.