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PubMed1986

Activation of phosphatidic acid metabolism of human erythrocyte membranes by perfringolysin O.

The effect of perfringolysin O on the lipid metabolism of human erythrocyte membranes was investigated. Erythrocytes were prelabeled with [3H]arachidonic acid and [32P]inorganic phosphate. In the presence of calcium ion(5.5 mM), the effect of perfringolysin O on lipid metabolism was very similar to that of an calcium-ionophore A23187. In the absence of calcium ion, the accumulation of phosphatidic acid and its following decreasing trend were observed during the reaction with the toxin. Such changes were not caused by filipin. These results suggest that perfringolysin O causes the activation of a diglyceride-phosphatidic acid cycle, which might be involved in the calcium transport.

Bacterial Toxins↗
PubMed1991

Divergent effects of propranolol on neutrophil superoxide release: involvement of phosphatidic acid and diacylglycerol as second messengers.

Relatively high levels of propranolol (170 microM) markedly attenuated the generation of 1,2 diacylglycerol in neutrophils stimulated with either FMLP plus cytochalasin B or with 20.0 mM NaF. This effect resulted from inhibition of phosphatidic acid phosphohydrolase as it was accompanied by a corresponding increase in the recovery of phosphatidic acid in organic extracts of stimulated cells. Although propranolol enhanced phosphatidic acid levels in neutrophils treated with FMLP alone, the drug had only a slight inhibitory influence on diglyceride generation in these cells. The effect of propranolol on enhancement of PA levels in neutrophils treated with FMLP alone strongly correlated with enhancement of FMLP-induced O2- generation. However, propranolol induced a similar dose-dependent inhibition of O2- generation in neutrophils stimulated with either FMLP + cytochalasin B or with 20.0 mM NaF. These results are consistent with the hypothesis that both phosphatidic acid and diacylglycerol are required for optimal initiation of neutrophil O2- release.

Cytochalasin B↗
PubMed1980

Enzymes of phospholipid synthesis: axonal versus Schwann cell distribution.

Using quantitative EM autoradiography to localize sites of incorporation of tritiated inositol and choline into mouse sciatic nerve, we observed a substantial axon-based phosphatidylinositol synthesis, but no axonal phosphatidylcholine synthesis. In the present communication we provide biochemical evidence for the axonal transport of CDP-diglyceride:inositol transferase (EC 2.7.8.11), the terminal enzyme in de novo phosphatidylinositol biosynthesis. Axonal transport of 1,2-diacyl-glycerol:CDP-choline choline phosphotransferase (EC 2.7.8.2), required for de novo phosphatidylcholine synthesis, was not apparent in these studies. During subcellular fractionation activities for the synthesis of phosphatidylinositol by inositol transferase (IT) and phosphatidylcholine by choline phosphotransferase (CPT) were recovered in crude microsomal fraction of rat sciatic nerve. However, CPT was much more highly enriched in the microsome fraction than IT, which may be an indication of the different subcellular localizations of these enzymes. Following ligation, we detected localized increases in the activities of both enzymes in 5 (and 3) mm segments taken immediately proximal and distal to the ligature. Both activities increased in a linear fashion in the proximal segments over the ensuing 72 h period. It took about 40 h (IT) and 56 h (CPT) for the activities in the segments proximal to the ligature to double compared to unligated contralateral (control) nerves. The time-dependent accumulation of IT was primarily due to axonal transport, while that of CPT was largely a result of increased enzyme activity in local Schwann cells. Evidence came from double ligation studies, where a proximal ligature, acting to restrict orthograde axonal transport, reduced accumulation in a distal ligature by 80% for IT, but only 28% for CPT. Conversely, blockage of the Schwann cell response with actinomycin D, reduced accumulation of CPT by 83% and IT by only 36%. Finally, light microscopic autoradiography was used to show that in the segment proximal to the ligature, tritiated inositol incorporation into lipid was primarily axonal, whereas that of tritiated choline remained primarily associated with Schwann cells.

Animals↗
PubMed1991

Activation mechanisms of platelet-activating factor in U937 cells: possible involvement of protein kinase C.

We have previously demonstrated that platelet-activating factor (PAF) binds specifically on cell membranes isolated from U937 cells. We now describe biological evidence showing that the effect of PAF on U937 cells is a receptor-mediated event. myo-[3H]Inositol-labeled U937 cells were used to investigate the possible role of phosphoinositide metabolism in these cells after binding of PAF. Formation of inositol phosphates (IP1, IP2, and IP3) in response to PAF was increased two- to threefold more than in vehicle control in U937 cells. The effect of PAF on endogenous protein phosphorylation was also studied by using 32PO4-labeled cells. PAF stimulates the phosphorylation of a 45-kDa protein in a time-dependent and dose-related fashion. Since the phospholipase C-generated diglyceride is an important activator of protein kinase C, the phosphorylated 45-kDa protein could be the substrate of protein kinase C. In this regard, we were able to demonstrate that phorbol ester enhances the phosphorylation of the same 45-kDa protein band. In addition, sphingosine, a protein kinase C inhibitor, inhibits the phosphorylation of the same 45-kDa protein band. Down-regulation of the protein kinase C also inhibits the 45-kDa protein phosphorylation. These results suggest that protein kinase C is involved in the PAF-U937 cell interaction.

Diglycerides↗
PubMed1976

The synthesis of chiral glycerides starting from D- and L-serine.

A method for synthesizing chiral glycerides starting from L- or D-serine is described. Optically-active serine (both enantiomers are commerically available) was transformed into glyceric acid by stereospecific diazotization. The configuration at carbon atom 2 was maintained during the reaction. The glyceric acid was then converted into optically pure isopropylideneglycerol - which is an important intermediate in the synthesis of mono-, di- and triglyderides - by esterification followed by acetalization with acetone and reduction with lithium aluminium hydride. Reaction of this intermediate with triphenylphosphine in tetrachloromethane followed by acid-catalysed hydrolysis and dehydrohalogenation provided optically-active glycidol (2,3-epoxy-1-propanol). The epoxy ring of an ester of glycidol and a fatty acid was then opened stereospecifically with retention of configuration by heating the glycidol ester in the presence of a second fatty acid and a catalyst. This yielded a chiral 1,3-diglyceride which could be converted into a chiral triglyceride.

Diglycerides↗
PubMed1976

Gas chromatographic analysis of synthetic glycidol esters, mono-, di- and triglycerides.

The gas chromatographic analysis of glycidol esters and mono-, di-,and triglycerides of palmitic-, stearic-, and oleic acid mixtures is described. The composition of the products was determined by gas chromatography on OV-17 after trimethylsilylation. Base-line separations between 1- and 2-monoglycerides and between 1,2- and 1,3-diglycerides were obtained. Isomerisation of the trimethylsilyl ethers of monoglycerides was not observed, contrary to published work.

Chromatography, Gas↗
PubMed1988

Polymorphic forms of 1,2-dipalmitoyl-sn-glycerol: a combined X-ray and electron diffraction study.

Quantitative crystallographic structure analyses are carried out for two polymorphic forms of 1,2-dipalmitoyl-sn-glycerol. A single crystal X-ray determination on the higher melting beta'L-form reveals that the hairpin conformer structure is essentially identical to that of the dilauroyl homolog reported earlier (I. Pascher, S. Sundell and H. Hauser (1981) J. Mol. Biol. 153, 791-806) with inclined acyl chain packing in the O perpendicular methylene subcell. Lamellar electron diffraction intensity data from epitaxially crystallized samples were used to determine the structure of the lower melting alpha L-form. The chains pack in the hexagonal subcell and are perpendicular to the lamellar surface. An appropriately oriented molecular model based on the beta'L-polymorph does not lead to a satisfactory structure solution but models based on the conformationally different 1,2-diglyceride moiety of several phospholipid structures does lead to a closer match to the observed diffraction data. In this proposed packing model for the alpha L-form, the hydroxyl oxygens are somewhat farther away from the unit cell origin than in the beta'L-form crystal structure, and, in combination with the different molecular conformation, this might explain the observed stability of this crystal polymorph against acyl shifts.

Crystallography↗
PubMed1995

Stereospecific labeling of the glycerol moiety: synthesis of 1,2-dioleoyl-sn-[3-3H]glycero-3-phospho(1-rac-glycerol).

1,2-Dioleoyl-sn-[3-3H]glycero-3-phospho(1-rac-glycerol) was synthesized from 1,2-dioleoyl-sn-glycerol using a new radiosynthetic procedure. 1,2-Dioleoyl-sn-glycerol was oxidized to the corresponding aldehyde using pyridinium dichromate and pyridine. The aldehyde was reduced to the radiolabeled alcohol using tritiated sodium borohydride and crown ether. This material was then converted to the phosphocholine derivative using 2-chloro-2-oxo-1,3,2-dioxaphospholane, followed by displacement with trimethylamine. In the last step, the 1,2-dioleoyl-sn-[3-3H]glycero-3-phosphocholine was converted to 1,2-dioleoyl-sn-[3-3H]glycero-3-phospho-(1-rac-glycerol) via a classic transphosphatidylation reaction using glycerol and cabbage phospholipase D. A theoretical explanation of unusual chemical behavior of the primary alcohol of diglycerides is also given, based on semi-empirical calculations.

Diglycerides↗
PubMed1996

Stereoselectivity of lipases in supercritical carbon dioxide. I. Dependence of the regio- and enantioselectivity of porcine pancreas lipase on the water content during the hydrolysis of triolein and its partial glycerides.

The stereoselectivity of porcine pancreas lipase (PPL) was investigated during the enzymatic hydrolysis of triolein and its partial glycerides in the presence of supercritical carbon dioxide (SCCO2) as reaction medium. The water content of the immobilized lipases was varied. The partial glycerides were separated into mono- and diglycerides by TLC, converted to their 3,5-dinitrophenylurethane derivatives and subsequently resolved into sn-1,2 and sn-2,3 enantiomers (estimation of dioleins) or into sn-1 and sn-3 enantiomers (estimation of monooleins) by HPLC on a chiral stationary phase (Sumichiral OA-4100). In all reactions under the conditions employed, PPL revealed a distinct preference for the sn-3 position of the glycerol. However, the stereoselectivity depends on the reaction time, the substances initially used and the enzyme water content. It seems that the effect of the enzyme water content on the activity and selectivity of porcine pancreas lipase in SCCO2 is based on a modification of the "micro-environment' of the enzyme by the solution of CO2 in water, causing a decrease of the pH value.

Animals↗
PubMed1984

Activation of phospholipase C in thrombin-stimulated platelets does not depend on cytoplasmic free calcium concentration.

Human platelets loaded with the fluorescent Ca2+ indicator quin2 and with different radioactive compounds including [3H]serotonin, [14C]arachidonic acid (AA) and [32P]orthophosphate were stimulated by thrombin under conditions producing secretion. In the absence of external Ca2+ (Ca2+e), cytoplasmic free [Ca2+], [Ca2+]i, increased to 340 nM, against 1685 nM at 1 mM [Ca2+]e. In both cases, diglyceride and phosphatidic acid production proceeded at the same rate, whereas AA release was inhibited at low [Ca2+]i. It is concluded that, at variance with phospholipase A2, phospholipase C activation does not depend on [Ca2+]i. These results give further support to the hypothesis of a Ca2+-independent pathway of cell activation involving phospholipase C and protein kinase C.

Arachidonic Acid↗
PubMed1986

Phorbol ester and 1,2-diolein are not fully equivalent activators of protein kinase C in respect to phosphorylation of membrane proteins in vitro.

Phosphorylation of liver plasma proteins by protein kinase C was studied by using the two best known activators of the enzyme, 12-O-tetradecanoylphorbol-13-acetate (TPA) and 1,2-diolein. While the effects of TPA and diolein were almost identical on two proteins and similar in magnitude on four proteins, the phosphorylation of an additional four proteins was increased only by TPA. We conclude that in respect to phosphorylation of membrane proteins, TPA and diglycerides are not fully equivalent activators of kinase C.

Animals↗
PubMed1987

Adenosine analogs with covalently attached lipids have enhanced potency at A1-adenosine receptors.

Chemically functionalized congeners of N6-phenyladenosine and 1,3-dipropyl-8-phenylxanthine have been covalently coupled to fatty acids, diglycerides, and a phospholipid. The lipid-drug conjugates inhibit R-[3H]-phenylisopropyladenosine binding to A1-adenosine receptors in rat cerebral cortex membranes. A xanthine-phosphatidylethanolamine conjugate bound with a Ki value of 19 nM. Various xanthine esters of low potency are potential prodrugs. Amides of an adenosine amine congener (ADAC) with 18-carbon fatty acids exhibited Ki values at A1-adenosine receptors of 70 pM, representing a 130-fold enhancement over the affinity of the corresponding acetyl amide. The very high affinity of adenosine-lipid conjugates may be due to stabilization of these adducts in the phospholipid microenvironment of the receptor protein.

Adenosine↗
PubMed1994

Diacylglycerol and alkylacylglycerol stimulate ram sperm phospholipase A2.

1. We have investigated the susceptibility of ram sperm phospholipase A2 (PLA2) to stimulation by diacyl- and alkylacylglycerols and by monoacyl- and monoalkylglycerols. 2. PLA2 activity in sonicates from ram spermatozoa was enhanced when 1-stearoyl-2-arachidonoyl-sn-glycerol, the diacylglycerol usually generated by polyphosphoinositide breakdown, was added to a radioactive phosphatidylcholine substrate; the effect was time- and Ca(2+)-dependent. 3. Both diacyl- and alkylacylglycerol considerably enhanced PLA2 activity; 1-O-hexadecyl-2-O-methyl-rac-glycerol, however, only showed slight stimulatory ability. 4. The monoradylglycerols 1-monohexadecanoyl-rac-glycerol, 2-monohexadecanoylglycerol, and 1-O-hexadecyl-sn-glycerol had very little effect on the enzyme's activity. 5. Exposure of spermatozoa to 1-oleoyl-2-acetyl-sn-glycerol (OAG) or 1-O-hexadecyl-2-acetyl-rac-glycerol (1-O-C16/2-C2), when cells were stimulated with the ionophore A23187 and Ca2+, resulted in higher PLA2 activity in sperm sonicates. Furthermore, parallel experiments showed that exocytosis was enhanced if spermatozoa were treated with A23187/Ca2+ and either OAG or 1-O-C16/2-C2. Since both diacyl- and alkylacylglycerols increased PLA2 activity and exocytosis, stimulation of PLA2 activity by these diglycerides may take place independently from protein kinase C activation.

Animals↗
PubMed1987

AD6 (8-monochloro-3-beta-diethylamino-ethyl-4-methyl-7-ethoxycarbonyl-meth oxy coumarin) inhibits the release of arachidonic acid in human platelets stimulated by thrombin.

The coumarin derivative AD6 is known to inhibit platelet aggregation and release and it possesses vasodilatory properties on coronary arteries of laboratory animals. Furthermore, the inhibition of the production of TxB2 from endogenous substrates after stimulation of human platelets with collagen has been demonstrated. The present report demonstrates that AD6 inhibits the production of labeled arachidonic acid and diglycerides from phospholipids of platelets stimulated with thrombin. This effect is dose-dependent and is already evident at a concentration of the drug (25 microM) which is unable to prevent the aggregation. Apparently, AD6 inhibits the release of arachidonic acid from phosphatidylinositol and choline phosphoglycerides which are the main sources of the substrate for the synthesis of prostaglandins and thromboxanes.

Arachidonic Acid↗
PubMed1986

In vivo modification of fatty acids and glycerides metabolism in response to 1,2,3,4,5,6-hexachlorocyclohexane and cythion exposure in the catfish, Clarias batrachus.

Specimens of either sex of the freshwater catfish, Clarias batrachus, were exposed to safe and sublethal concentrations of gamma-BHC (2 and 8 ppm) and cythion (1 and 4 ppm) for 4 weeks during different phases of annual reproductive cycle. Their effects on free fatty acids (FFA) and acyl glycerides, viz., monoglycerides (MG), diglycerides (DG), and triglycerides (TG), were studied in liver, plasma, gonads, and muscle. During the preparatory phase, both pesticides suppressed the levels of FFA and acylglycerides (MG, DG, and TG) in liver of either sex but had no effect on their levels in plasma, ovary, and muscle; however, FFA and TG were reduced in testis. Unlike the preparatory phase, in the prespawning phase different lipids responded variedly to the concentrations of both Cythion and gamma-BHC. In the female, FFA in liver and plasma was raised but in ovary and muscle it was decreased. Acylglycerides in studied tissues were also reduced except ovarian TG which was increased by both pesticides at safe concentrations. Contrary to this, in the male these lipids were raised in liver and testis. Moreover, during the spawning phase, these pesticides enhanced the hepatic FFA together with acylglycerides in the female but failed to elicit any change in their levels in the male. Plasma levels of FFA and TG were reduced in the female; however, in the male FFA was raised and TG remained unchanged. Ovarian FFA and TG were decreased and increased, respectively. During the postspawning phase, none of the lipid fractions could be affected in the male except hepatic FFA which was reduced; however, in the female TG along with FFA was decreased.

Animals↗
PubMed1986

A study of the membrane attachment site of the membrane-form variant surface glycoprotein from Trypanosoma brucei brucei using lipid vesicles as a model of the plasma membrane.

The incorporation of the membrane form and the soluble form of variant surface glycoprotein (mfVSG and sVSG) from Trypanosoma brucei brucei into liposomes has been investigated. It was found that selective incorporation of mfVSG into liposomes was possible in the presence of 8 M urea as a denaturing agent; sVSG, by contrast, was incorporated only poorly into liposomes. After proteolysis of mfVSG incorporated into liposomes, a compound was isolated from the liposomes which carries with it constituents of the glyophospholipid membrane anchor: ethanolamine, di-14:0-diglyceride and phosphatidylinositol were identified by electron impact and fast atom bombardment mass spectrometry, thus providing direct confirmation of the earlier findings of Holder [Holder, A.A. (1983) Biochem. J. 209, 261-262] and Ferguson et al. [Ferguson, M.A.J., Haldar, K. and Cross, G.A.M. (1985) J. Biol. Chem. 260, 4963-4968; Ferguson, M.A.J., Low, M.G. and Cross, G.A.M. (1985) J. Biol. Chem. 260, 14547-14555].

Animals↗
PubMed1981

Inhibition by Ca2+ of the incorporation of myo-inositol into phosphatidylinositol.

The incorporation of myo-[2-3H]inositol into phosphatidylinositol of the aorta and the vas deferens was measured and the effects of Ca2+ and other divalent cations were determined. When incubated in normal Krebs-Ringer buffer, only negligible radioactivity was incorporated into aorta slices. Mn2+ increased the incorporation greatly. The enhanced incorporation was attributable to an increase in CDP-diglyceride:inositol transferase activity, rather than the myo-inositol exchange reaction. Transferase activity was increased 20-fold by 1 mM Mn2+, in the presence of 20 mM Mg2+. The Mn2+-stimulated activity was strongly inhibited by Ca2+. In the absence of Mn2+, but presence of 20 mM Mg2+, transferase activity was inhibited 80% by 0.01 mM Ca2+. Removal of endogenous Ca2+ from the tissue by ionophore A23187 and EGTA increased the incorporation of myo-[2-3H]inositol into phosphatidylinositol. These findings indicate that Ca2+ inhibited the synthesis of phosphatidylinositol. The proposed action of cholinergic and alpha-adrenergic agonists in enhancing the degradation and turnover of phosphatidyl-inositol and in provoking the influx of Ca2+ should be unfavorable to the recovery of cellular phosphatidylinositol content.

Animals↗
PubMed1988

Activators of protein kinase C and phenylephrine depolarize the astrocyte membrane by reducing the K+ permeability.

The membrane potential of astrocytes has been measured by monitoring the absorbance of a cyanine dye DiS-C2-(5). Ba2+, the phorbol ester 12-tetradecanoylphorbol myristateacetate (TPA) and the diglyceride, dioctanoylglycerol (DiC8) depolarize the membrane. Valinomycin which makes the membrane potential dependent on the K+ electrochemical potential evokes a hyperpolarization when added subsequently. The alpha-adrenergic receptor agonist phenylephrine was blocked by Ba2+, TPA, DiC8 and valinomycin. The results suggest that a protein kinase C-mediated reduction in the K+ permeability is responsible for the depolarizing effect of TPA, DiC8 and phenylephrine.

Animals↗