Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “PHOSPHATIDES”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3Linked to original sources
PubMed1990

Kinetic analysis of yeast phosphatidate phosphatase toward Triton X-100/phosphatidate mixed micelles.

A detailed kinetic analysis of purified yeast membrane-associated phosphatidate phosphatase was performed using Triton X-100/phosphatidate mixed micelles. Enzyme activity was dependent on the bulk and surface concentrations of phosphatidate. These results were consistent with the "surface dilution" kinetic scheme (Deems, R. A., Eaton, B. R., and Dennis, E. A. (1975) J. Biol. Chem. 250, 9013-9020) where phosphatidate phosphatase binds to the mixed micelle surface before binding to its substrate and catalysis occurs. Phosphatidate phosphatase was shown to physically associate with Triton X-100 micelles in the absence of phosphatidate, however, the enzyme was more tightly associated with micelles when its substrate was present. The enzyme had 5- to 6-fold greater affinity (reflected in the dissociation constant nKsA/chi) for Triton X-100 micelles containing dioleoyl-phosphatidate and dipalmitoyl-phosphatidate when compared to micelles containing dicaproyl-phosphatidate. The Vmax for dioleoyl-phosphatidate was 3.8-fold higher than the Vmax for dipalmitoyl-phosphatidate, whereas the interfacial Michaelis constant chi KmB for dipalmitoyl-phosphatidate was 3-fold lower than the chi KmB for dioleoyl-phosphatidate. The specificity constants (Vmax/chi KmB) of both substrates were similar which indicated that dioleoyl-phosphatidate and dipalmitoyl-phosphatidate were equally good substrates. Based on catalytic constants (Vmax and chi KmB), dicaproyl-phosphatidate was the best substrate with an 11- and 14-fold greater specificity constant when compared to dioleoyl-phosphatidate and dipalmitoyl-phosphatidate, respectively.

Catalysis↗
PubMed1999

Induction of endothelial monolayer permeability by phosphatidate.

Released into the vasculature from disrupted cells or transported to the surface of adjacent effectors, phosphatidate and related lipids may potentiate endothelial cell activation. However, the effect of these lipids on endothelial monolayer barrier integrity has not been reported. The present study documents the induction of endothelial monolayer permeability by phosphatidate. Both long (di-C18:1) and medium (di-C10; di-C8) chain length phosphatidates increased permeability of bovine pulmonary artery endothelial cell monolayers assessed using a well characterized assay system in vitro. Barrier disruption effected by dioctanoyl (di-C8) phosphatidate was markedly potentiated by the addition of propranolol, an inhibitor of endothelial cell "ecto"-phosphatidate phosphohydrolase (PAP), a lipid phosphate phosphohydrolase (LPP) that efficiently hydrolyzes extracellular substrate. Disruption of barrier function by phosphatidate did not result from its non-specific detergent characteristics, since a non-hydrolyzable but biologically inactive phosphonate analog of dioctanoyl phosphatidate, which retains the detergent characteristics of phosphatidate, did not induce permeability changes. Furthermore, neither diacylglycerol nor lyso-PA effected significant increases in monolayer permeability, indicating the observed response was due to phosphatidate rather than one of its metabolites. Phosphatidate-induced permeability was attenuated by preincubation of endothelial cells with the tyrosine kinase inhibitor, herbimycin A (10 microg/ml), and enhanced by the tyrosine phosphatase inhibitor, vanadate (100 microM), implicating a role for activation of intracellular tyrosine kinases in the response. In addition, phosphatidate increased the levels of intracellular free Ca(2+) in endothelial cells and ligated specific binding sites on endothelial cell plasma membranes, consistent with the presence of a phosphatidate receptor. Since phosphatidate generated within the plasma membrane of adherent effectors potentially interacts with endothelial membranes, we evaluated the influence of phosphatidate-enriched neutrophil plasma membranes on endothelial monolayer integrity. The effects of ectopic phosphatidate on endothelial monolayer permeability were mimicked by phosphatidate confined to neutrophil plasma membranes. We conclude that phosphatidate may be a physiologic modulator of endothelial monolayer permeability that exerts its effects by activating a receptor-linked, tyrosine kinase-dependent process which results in mobilization of intracellular stored Ca(2+)and consequent metabolic activation.

Animals↗
PubMed1979

Effects of ionization and counterion binding on the surface areas of phosphatidic acids in monolayers.

At 24-26 degrees C, force-area isotherms show that unionized dipalmitoyl phosphatidic acid forms a solid-condensed film while unionized egg and dioleoyl phosphatidic acids form liquid-expanded films. Surface area is a characteristic feature of a specific phosphatidic acid and the purity of a phosphatidic acid preparation can be established by the surface area of the unionized phosphatidic acid (acid subphase) at 17 dynes/cm (castor oil piston). Ionized dipalmitoyl phosphatidic acid desorbs from a monolayer at a measurable rate while ionized egg and dioleoyl phosphatidic acids desorb too slowly for rate studies. The apparent surface pK(2) for dipalmitoyl phosphatidic acid, calculated from desorption rates, is 9.4. Surface areas of the phosphatidic acids expand with ionization. Solid dipalmitoyl phosphatidic acid films expand only in the pK(2) region, showing one inflection point which indicates that the K(1)/K(2) ratio is less than 100 and that, as a consequence of this ratio, the apparent surface pK(1) is greater than 7.4. Liquid egg and dioleoyl phosphatidic acid films have two inflection points, expanding in both the pK(1) and pK(2) regions. The apparent surface pK(1) and pK(2) values, calculated from inflection points in surface area data, are 3.5 and 8.0, respectively. Film expansion with phosphatidate anions is less than anticipated, showing the presence of weak transient hydrogen bonds. Expanded phosphatidate anion films are condensed by alkaline earth cations. The Ca(2+) and Ba(2+) salts of completely ionized phosphatidic acids collapse from monolayers, showing that the phosphatidate anion may function as an ionophore for the transport of alkaline earth ions.-Patil, G. S., N. J. Dorman, and D. G. Cornwell. Effects of ionization and counterion binding on the surface areas of phosphatidic acids in monolayers.

Barium↗
PubMed1980

Inhibition of cyclic AMP accumulation in hamster adipocytes with phosphatidic acid: differences and similarities with alpha adrenergic effects.

Clark et al (Journal of Cyclic Nucleotide Research 6:37 (1980)) demonstrated phosphatidic acid inhibition of cyclic AMP formation in WI-38 fibroblasts and suggested the hypothesis that cholinergic inhibition of adenylate cyclase is mediated through accumulation of this phospholipid. In view of these data, we tested the hypothesis that phosphatidic acid is involved in alpha-adrenergic inhibition of cyclic AMP formation in hamster adipocytes. The effects of phosphatidic acid on hormone and methyl xanthine stimulated cyclic AMP accumulation and lipolysis were studied. Phosphatidic acid inhibited 3-isobutyl-1-methyl xanthine (IBMX) stimulated cyclic AMP formation. The maximum inhibition (85% to 100%) of IBMX stimulated cyclic AMP accumulation was detected at 1.0 microM phosphatidic acid. When lipolysis was measured, however, inhibitory effects of phosphatidic acid were not evident until the concentration of phospholipid was increased to 300 microM. The cyclic AMP lowering and antilipolytic effects were detected using egg yolk phosphatidic acid, dipalmitoyl phosphatidic acid, dimyristoyl phosphatidic acid, distearoyl phosphatidic acid and palmitoyl lysophosphatidic acid but not with phosphatidylinositol, phosphatidylserine, phosphatidylethanolamine, phosphatidylcholine or 1,2- diglyceride. In contrast to phosphatidic acid, clonidine or N6-phenylisopropyl adenosine inhibited lipolysis in concert with inhibition of methyl xanthine stimulated cyclic AMP accumulation. Cyclic AMP accumulation increased by isoproterenol in combination with IBMX was partially blocked by clonidine but not by phosphatidic acid. These results show similarities as well as differences between clonidine and phosphatidic acid actions on hamster fat cells and do not, therefore, provide unequivocal support for the possibility that phosphatidic acid is intimately involved in alpha-adrenergic effects on hamster adipocytes. However, the high selectivity of phosphatidic acid suggests a physiological role of this agent in regulation of adenylate cyclase.

1-Methyl-3-isobutylxanthine↗
PubMed1997

Characterization and purification of neutrophil ecto-phosphatidic acid phosphohydrolase.

Phosphatidic acid and its derivatives play potentially important roles as extracellular messengers in biological systems. An ecto-phosphatidic acid phosphohydrolase (ecto-PAPase) has been identified which effectively regulates neutrophil responses to exogenous phosphatidic acid by converting the substrate to diacylglycerol. The present study was undertaken to characterize this ecto-enzyme on intact cells and to isolate the enzyme from solubilized neutrophil extracts. In the absence of detergent, short chain phosphatidic acids were hydrolysed most effectively by neutrophil plasma membrane ecto-PAPase; both saturated and unsaturated long chain phosphatidic acids were relatively resistant to hydrolysis. Both long (C18:1) and short (C8) chain lyso-phosphatidic acids were hydrolysed at rates comparable with those observed for short chain (diC8) phosphatidic acid. Activity of the ecto-enzyme accounted for essentially all of the N-ethylmaleimide-insensitive, Mg2+-independent PAPase activity recovered from disrupted neutrophils. At 37 degrees C and pH7.2, the apparent Km for dioctanoyl phosphatidic acid (diC8PA) was 1. 4x10(-3) M. Other phosphatidic acids and lysophosphatidic acids inhibited hydrolysis of [32P]diC8PA in a rank order that correlated with competitor solubility, lysophosphatidic acids and unsaturated phosphatidic acids being much more effective inhibitors than long chain saturated phosphatidic acids. Dioleoyl (C18:1) phosphatidic acid was an unexpectedly strong inhibitor of activity, in comparison with its ability to act as a direct substrate in the absence of detergent. Other inhibitors of neutrophil ecto-PAPase included sphingosine, dimethyl- and dihydro-sphingosine, propranolol, NaF and MgCl2. Of several leucocyte populations isolated from human blood by FACS, including T cells, B cells, NK lymphocytes and monocytes, ecto-PAPase was most prevalent on neutrophils; erythrocytes were essentially devoid of activity. A non-hydrolysable, phosphonate analogue of phosphatidic acid, phosphonate 1, efficiently solubilized catalytic activity from intact neutrophils without causing cell disruption or increasing permeability. Enzyme activity in solubilized extracts was purified in the absence of detergent by successive heparin-Sepharose, gel filtration and anion exchange chromatography. By assaying activity in renatured SDS/polyacrylamide gel slices, the molecular mass of neutrophil ecto-PAPase was estimated to be between 45 and 52 kDa, similar to the molecular mass of previously purified plasma membrane PAPases. Since a large portion of neutrophil plasma membrane PAPase is available for hydrolysis of exogenous substrates, ecto-PAPase may play an important role in regulating inflammatory cell responses to extracellular phosphatidic acid in biological systems.

Cell Membrane↗
PubMed1984

Ca2+-dependent conversion of phosphatidylinositol to phosphatidate in neutrophils stimulated with fMet-Leu-Phe or ionophore A23187.

Human and rabbit neutrophils stimulated with formylmethionyl-leucyl-phenylalanine (fMet-Leu-Phe) and A23187 show a loss of phosphatidylinositol and an increase in phosphatidate. In cells prelabelled with 32Pi it would be expected that the newly synthesised phosphatidate would have the same specific activity as cellular ATP, provided that the loss of phosphatidylinositol is by phospholipase C attack and the resultant diacyglycerol is phosphorylated by ATP. Instead, it is demonstrated that the specific activity of newly-formed phosphatidate is less than a tenth of the specific activity of ATP initially followed by a gradual increase. The time-course of mass and of [3H]glycerol-labelled phosphatidate formation (from cells pulse-labelled with [3H]glycerol) is similar to enzyme release but differs from the generation of 32P-labelled phosphatidate (from cells prelabelled with 32Pi). The source of the newly formed phosphatidate is most likely from phosphatidylinositol because: (a) The increase in phosphatidate is always accompanied by a loss of phosphatidylinositol with no changes in the other lipids. (b) Cells pulse-labelled with [3H]glycerol lose label from phosphatidylinositol only and this is accompanied by an increase in label in phosphatidate. (c) The specific activity of the newly synthesised phosphatidate is closest to the specific activity of phosphatidylinositol. One plausible explanation for these results is that phosphatidylinositol is directly converted to phosphatidate by phospholipase D action and the resulting phosphatidate accumulates radioactivity by exchange of its phosphate group with ATP. It is also shown that enzyme secretion and conversion of phosphatidylinositol to phosphatidate can depend on both intra- as well as extracellular Ca2+. Depletion of the intracellular pool of Ca2+ is essential to inhibit totally the enzyme secretion and the conversion of phosphatidylinositol to phosphatidate in agreement with our previous results on rabbit neutrophils (Cockcroft, S., et al. (1981) Biochem. J. 200, 501-508).

Adenosine Triphosphate↗
PubMedDate not supplied

Monolayer characteristics and thermal behaviour of phosphatidic acids.

The monolayer and thermal behaviour of different phosphatidic acids are presented. At neutral pH and 22 degrees C dilauroylphosphatidic acid and unsaturated phosphatidic acids form liquid-expanded monolayers, while dipalmitoyl- and distearoylphosphatidic acid form condensed monolayers. Dimyristoylphosphatidic acid undergoes a transition from the liquid-expanded to the condensed state. With long-chain saturated and unsaturated phosphatidic acids little change in molecular area is observed between pH 2 and 7. In contrast, the short chain saturated phosphatidic acids, dilauroyl- and dimyristoylphosphatidic acids, undergo a condensation in the pH range 2 to 7. This is so in spite of the fact that the phosphoric acid group dissociates and the phosphatidic acid molecule attains one negative charge over this pH range. This finding is interpreted to indicate that the electrostatic repulsion between negatively charged phosphatidic acid molecules is compensated for or even outweighed by other intermolecular forces. Hydrogen bonding at the lipid/water interface is supposed to play a major role. All phosphatidates studied exhibit a significant expansion in the pH range 7 to 12. The second apparent pK of the primary phosphate group of phosphatidic acids is 8.6 and the expansion observed in this pH range is therefore due to electrostatic repulsion. At neutral pH the ether analogues of saturated phosphatidic acids have monolayer properties similar to those of the ester compounds. Considering the total pH range of 2 to 12 studied the force-area curves of the ether analogues are more condensed compared to the ester compounds. Synthetic phosphatidates and their ether analogues give reversible sharp crystal(gel)-to-liquid crystal transitions while the naturally occurring egg phosphatidate gives a broad, asymmetric one. The transition temperature Tm of saturated phosphatidates increases with increasing hydrocarbon chain length and at a given chain length Tm decreases markedly with unsaturation. The Tm values of the ether analogues are about 10 degrees C higher and the delta H values are 10-15% lower than those of the corresponding esters.

Calorimetry, Differential Scanning↗
PubMed1995

Phosphatidic acid and lysophosphatidic acid induce haptotactic migration of human monocytes.

The present study was aimed at defining the chemotactic activity of phosphatidic acid, which is rapidly produced by phagocytes in response to chemotactic agonists. Exogenously added phosphatidic acid induced human monocyte directional migration across polycarbonate filters with an efficacy (number of cell migrated) comparable to that of "classical" chemotactic factors. In lipid specificity studies, activity of phosphatidic acid decreased with increasing acyl chain length but was restored by introducing unsaturation in the acyl chain with the most active form being the natural occurring 18:0,20:4-phosphatidic acid. Lysophosphatidic acid was also active in inducing monocyte migration. No other phospholipid and lysophospholipid tested was effective in this response. Monocyte migration was regulated by a gradient of phosphatidic acid and lysophosphatidic acid bound to the polycarbonate filter, in the absence of detectable soluble chemoattractant. Migration was also observed if phospholipids were bound to fibronectin-coated polycarbonate filters. Thus, phosphatidic acid and lysophosphatidic acid, similarly to other physiological chemoattractants (e.g. C5a and interleukin-8), induce cell migration by an haptotactic mechanism. Phosphatidic acid caused a rapid increase of filamentous actin and, at higher concentrations, induced a rise of intracellular calcium concentration. Monocyte migration to phosphatidic acid and lysophosphatidic acid, but not to diacylglycerol, was inhibited in a concentration-dependent manner by Bordetella pertussis toxin, while cholera toxin was ineffective. In the chemotactic assay, phosphatidic acid and lysophosphatidic acid induced a complete homologous desensitization and only partially cross-desensitized one with each other, or with diacyl-glycerol and monocyte chemotactic protein-1. Suramine inhibited monocyte chemotaxis with a different efficiency phosphatidic acid > lysophosphatidic acid" diacyl-glycerol On the contrary, monocyte chemotactic protein-1-induced chemotaxis was not affected by the drug. Collectively, these data show that phosphatidic acid induces haptotactic migration of monocytes that is at least in part receptor-mediated. These results support a role for phosphatidic acid and lysophosphatidic acid in the regulation of leukocyte accumulation into tissues.

Actins↗