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PubMed1985

Effects of replacement of the hydroxyl group of cholesterol and tocopherol on the thermotropic behavior of phospholipid membranes.

The role of the hydroxyl groups of cholesterol and tocopherol in mediating their interaction with phospholipid bilayers has been a subject of considerable interest. We have examined this question by using derivatives of cholesterol and tocopherol in which the hydroxyl group is esterified to succinate. The hemisuccinate esters of cholesterol and alpha-tocopherol can be readily incorporated into phospholipid membranes and in fact can by themselves form closed membrane vesicles as demonstrated by the encapsulation of [3H]sucrose. The thermotropic behavior of mixtures containing each succinate ester and phospholipid was studied by differential scanning calorimetry. The effect of cholesteryl hemisuccinate on the thermotropic properties of dipalmitoylphosphatidylcholine and dimyristoylphosphatidylethanolamine is very similar to that of cholesterol. This indicates that the 3 beta-OH is not required for the formation of a cholesterol-phospholipid complex. In mixtures of tocopherol acid succinate and phospholipids the peak transition temperature is progressively shifted to lower temperatures as the mole fraction of alpha-tocopherol succinate is increased, while the enthalpy of the transition is only slightly affected. At a tocopherol succinate/phospholipid molar ratio of 9/1 a phase transition is still detectable. A comparison between tocopherol succinate and tocopherol indicates that the substitution of the hydroxyl group reduces the interaction of tocopherol with phospholipids to a small but measurable extent. Thus, the hydroxyl group of tocopherol is more important than the hydroxyl group of cholesterol in influencing their interactions with phospholipids.

Chemical Phenomena↗
PubMed1987

Association of protein kinase C with phospholipid vesicles.

The Ca2+- and phospholipid-dependent protein kinase, protein kinase C (PKC), was purified from bovine brain by a modified procedure that provided sufficient quantities of stable protein for analysis of physical properties of protein-membrane binding. The binding of PKC to phospholipid vesicles of various compositions was investigated by light-scattering and fluorescence energy transfer measurements. The binding properties for membranes of low phosphatidylserine (PS) content were consistent with a peripheral membrane association; PKC showed Ca2+ -dependent binding to phospholipid vesicles containing phosphatidylserine, phosphatidylinositol, or phosphatidylglycerol. Membranes containing 0-20% PS (the remainder of the phospholipid was phosphatidylcholine) bound less protein than membranes containing greater than 20% PS; the factor limiting protein binding to membranes containing low PS appeared to be the availability of acidic phospholipids. Increasing the PS content above 20% did not increase the amount of membrane-bound protein at saturation, and the limiting factor was probably steric packing of protein on the membrane surface. The membranes bound about 1 g of protein/g of phospholipid at steric saturation. Binding was of relatively high affinity (Kd less than 5 nM), and the association rate was rapid on the time scale of the experiments. Addition of ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid to phospholipid-bound PKC caused dissociation of the complex, and the properties of this dissociation indicated an equilibrium binding of protein to membrane. However, only partial dissociation of PKC was achieved when the PS content of the vesicles exceeded 20%. A number of comparisons revealed that binding of protein to the membrane, even in the presence of phorbol esters, was insufficient for development of enzyme activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1998

Calcium-triggered selective intermembrane exchange of phospholipids by the lung surfactant protein SP-A.

It is shown that human lung surfactant protein (SP-A) mediates selective exchange of phospholipid probes with unlabeled phospholipid in excess vesicles in the presence of calcium and NaCl. The exchange occurs without leakage of vesicle contents, or transbilayer movement (flip-flop) of the phospholipid probes, or fusion of vesicles. Individual steps preceding the exchange are dissected by a combination of protocols, and the results are operationally interpreted in terms of a model where a calcium-dependent change in SP-A triggers aggregation of vesicles followed by probe exchange between the vesicles in contact through SP-A. The contacts remain stable in the presence of calcium; i.e., the vesicles in contact do not change their partners on the time scale of several minutes. The binding of SP-A to vesicles and the aggregation of vesicles are rapid, and the aggregation is rapidly reversed by EGTA; i.e., both the forward and reverse aggregation reactions are complete in about 1 min. The exchange rate of the various probes between aggregated vesicles below 1 mM calcium in the presence of NaCl shows selectivity, i.e., a modest dependence on the net anionic charge on vesicles and for the headgroup of the probe. Exchange with lower selectivity is seen at >2 mM Ca in the absence of NaCl. SP-A binding to vesicles does not show an absolute specificity for the phospholipid structure, but the time course of the subsequent changes does. The results suggest that SP-A contacts between phospholipid interfaces could mediate the exchange of phospholipid species (trafficking and sorting) between lung surfactant pools in the hypophase and all accessible phospholipid interfaces of the alveolar space.

Calcium↗
PubMed1997

Membrane integrity and phospholipid movement influence the base exchange reaction in rat liver microsomes.

Properties of Ca(2+)-stimulated incorporation of amincalcohols, serine and ethanolamine, into phospholipids, and factors regulating the reaction were studied in endoplasmic reticulum membranes isolated from rat liver. In contrast to apparent K(m) values for either aminoalcohol, maximal velocities of the reaction were significantly affected by Ca2+ concentration. No competition between these two soluble substrates used at equimolar concentrations close to their K(m) values was observed, suggesting the existence of two distinct phospholipid base exchange activities. The enzyme utilizing the electrically neutral serine was not sensitive to changes of membrane potential evoked by valinomycin in the presence of KCl. On the other hand, when positively charged ethanolamine served as a substrate, the enzyme activity was inhibited by 140 mM KCl and this effect was reversed by valinomycin. The rates of inhibition of phospholipid base exchange reactions by various thiol group modifying reagents were also found to differ. Cd2+ and lipophylic p-chloromercuribenzoic acid at micromolar concentrations were most effective. It can be suggested that -SH groups located within the hydrophobic core of the enzymes molecules are essential for the recognition of membrane substrates. However, the influence of the -SH group modifying reagents on the protein-facilitated phospholipid motion across endoplasmic reticulum membranes can not be excluded, since an integral protein-mediated transverse movement of phospholipids within the membrane bilayer and Ca(2+)-mediated changes in configuration of the phospholipid polar head groups seem to be a regulatory step of the reaction. Indeed, when the membrane integrity was disordered by detergents or an organic solvent, the reaction was inhibited, although not due to the transport of its water-soluble substrates is affected, but due to modulation of physical state of the membrane bilayer and, in consequence, the accessibility of phospholipid molecules.

Animals↗
PubMed2001

Stimulation of plant plasma membrane Ca2+-ATPase activity by acidic phospholipids.

The effect of phospholipids on the activity of the plasma membrane (PM) Ca2+-ATPase was evaluated in PM isolated from germinating radish (Raphanus sativus L. cv. Tondo Rosso Quarantino) seeds after removal of endogenous calmodulin (CaM) by washing the PM vesicles with EDTA. Acidic phospholipids stimulated the basal Ca2+-ATPase activity in the following order of efficiency: phosphatidylinositol 4,5-diphosphate (PIP2) approximately phosphatidylinositol 4-monophosphate>phosphatidylinositol approximately phosphatidylserine approximately phosphatidic acid. Neutral phospholipids as phosphatidylcholine and phosphatidylethanolamine were essentially ineffective. When the assays were performed in the presence of optimal free Ca2+ concentrations (10 &mgr;M) acidic phospholipids did not affect the Ca2+-ATPase activated by CaM or by a controlled trypsin treatment of the PM, which cleaved the CaM-binding domain of the enzyme. Analysis of the dependence of Ca2+-ATPase activity on free Ca2+ concentration showed that acidic phospholipids increased Vmax and lowered the apparent Km for free Ca2+ below the value measured upon tryptic cleavage of the CaM-binding domain; in particular, PIP2 was shown to lower the apparent Km for free Ca2+ of the Ca2+-ATPase also in trypsin-treated PM. These results indicate that acidic phospholipids activate the plant PM Ca2+-ATPase through a mechanism only partially overlapping that of CaM, and thus involving a phospholipid-binding site in the Ca2+-ATPase distinct from the CaM-binding domain. The physiological implications of these results are discussed.

Journal Article↗
PubMed1986

Inositol phospholipid arachidonic acid metabolism in GH3 pituitary cells.

Inositol phospholipids in cultured GH3 cells, a prolactin secreting, thyrotropin-releasing hormone (TRH) sensitive rat pituitary cell line, exhibit a preferential selectivity for incorporating arachidonic acid. Fatty acid composition data show that all inositol phospholipids are enriched in stearic and arachidonic acids to a much greater degree than other cellular phospholipids. Incubation of GH3 cells with radioactive stearate, oleate, arachidonate, eicosapentaenoate or docosahexaenoate also showed that much more stearate and arachidonate were incorporated into inositol phospholipids. In short term incubations with tracer amounts of radioactive arachidonate, incorporation was initially into phosphatidylinositol (PtdIns), with phosphatidylinositol 4-phosphate (PtdIns4P), and phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] being labelled at later times. During longer incubations, all of the inositol phospholipids reach equilibrium at about 10 h, and the resulting specific activities of the three fractions were similar. These findings suggest that arachidonate is incorporated initially into PtdIns and that PtdIns is then phosphorylated. There was no release of either arachidonate or eicosanoid products when GH3 cells were incubated with TRH. However, TRH stimulation of 32P-labelled GH3 cells resulted in rapid breakdown of PtdIns(4,5)P2 and PtdIns4P, with concomitant increases in [32P]phosphatidic acid and [32P]PtdIns. When the [32P]PtdIns was further analysed by argentation chromatography to separate PtdIns molecular species, it was found that tetraenoic (stearate/arachidonate) species accounted for 80% of the stimulated labelling. The selectivity for arachidonate incorporation into inositol phospholipids coupled with turnover of the arachidonate-containing molecular species suggests that inositol phospholipids containing arachidonic acid or the diacylglycerol resulting therefrom may play a vital cellular role in GH3 cells. This role may involve the operation of the PtdIns cycle itself rather than a stimulated release of arachidonate for eicosanoid formation.

Animals↗
PubMed1986

A difference infrared-spectroscopic study of the interaction of ubiquinone-10 with phospholipid bilayers.

The interaction between 1,2-dipalmitoyl phosphatidylcholine and ubiquinone-10 in aqueous systems was studied by difference i.r. spectroscopy. Binary mixtures of the two lipids in proportions of 2, 5 and 15 mol% were investigated in the spectral regions reporting on the hydrocarbon chains of the phospholipid and the polar phosphate group. No spectral shifts or significant broadening of any absorbances due to the phospholipid were detected at temperatures of 20 or 54 degrees C. Changes in the frequency of the maximum of the CH2 antisymmetric C-H stretching vibration with temperature indicated that the gel-to-liquid-crystal-line phase-transition temperature of the phospholipid was lowered by about 2 degrees C in the presence of between 2 and 15 mol% ubiquinone-10. Absorbance by the benzoquinone substituent of ubiquinone-10 was detected by spectral subtraction of dispersions of phospholipid alone. Bands due to C = O stretching and ester group vibrations of ubiquinone-10 in co-dispersion with phospholipid were compared with the same spectral region when ubiquinone-10 was dissolved in solvents or as a crystalline solid. Spectral changes could be detected when ubiquinone-10 in phospholipid was compared with solution in dodecane and chloroform. These may indicate that the benzoquinone ring system is located within a hydrocarbon domain in dispersions with dipalmitoyl phosphatidylcholine. It was concluded from the study that when ubiquinone-10 is co-dispersed with dipalmitoyl phosphatidylcholine in water the two lipids phase-separate. There is no evidence that ubiquinone-10 intercalates between phospholipid molecules, which undergo a gel-liquid-crystalline phase transition in only a slightly modified form. The data suggest that the benzoquinone substituent resides in a hydrophobic domain and that aggregates spanning the bilayer are a possible arrangement of the ubiquinone in the structure.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1999

Qualitative and quantitative studies of autoantibodies to phospholipids in diabetes mellitus.

Diabetes mellitus is associated with vascular and neurological complications. We have investigated the presence of antibodies to phospholipids and to phospholipid binding plasma proteins in blood samples collected from 68 clinically and biochemically characterized type I and type II diabetic patients and from 252 healthy blood donor controls. Each sample was analysed for antibodies to three phospholipids (cardiolipin, phosphatidylserine and phosphatidylethanolamine), the antibody isotypes (IgA, IgG and IgM), and whether antibody activity was plasma protein-dependent. Patients were considered to have anti-phospholipid antibodies when one or more of these 18 tests was found above predetermined control values. The results of these experiments revealed an increased incidence of anti-phospholipid antibodies in diabetic patients compared with control subjects. The incidence of IgA isotype to phosphatidylethanolamine was higher than the incidence of other isotypes to other phospholipids, and their reactivities were independent of phospholipid-associated proteins. In addition, these antibody findings were studied for associations with prothrombin degradation products, activated factor VII and activated protein C, and with the incidence of diabetic complications. The anti-phosphatidylethanolamine antibody association with proliferative retinopathy was significant.

Adult↗
PubMed2001

Compensatory phospholipid digestion is required for cholesterol absorption in pancreatic phospholipase A(2)-deficient mice.

BACKGROUND AND AIMS: Numerous studies have suggested phospholipid inhibition of dietary cholesterol absorption through the gastrointestinal tract. This study addressed the importance of luminal phospholipid hydrolysis in this process. METHODS: The effect of phospholipase inhibition on cholesterol transport from intestinal lumen to the lymphatics was evaluated in lymph fistula rats. Cholesterol and phospholipid absorption efficiency in intact animals was evaluated in control and phospholipase A(2) (PLA2) gene-targeted mice. RESULTS: The PLA2 inhibitor FPL 67047XX retarded cholesterol absorption in a lymph fistula rat model. Under basal chow-fed dietary conditions, cholesterol absorption efficiency from a single bolus meal, and plasma lipid levels, were similar among PLA2+/+, PLA2+/-, and PLA2-/- mice. Interestingly, the nonhydrolyzable phospholipid dioleoyl ether phosphatidylcholine suppressed cholesterol absorption by 10% to 18% in mice without regard to their PLA2 genotype. When 1-palmitoyl-2-[(14)C]oleoyl-phosphatidylcholine was used as the substrate, the radiolabeled phospholipid was found to be hydrolyzed and absorbed with equal efficiency in PLA2+/+, PLA2+/-, and PLA2-/- mice. CONCLUSIONS: These results suggested that although phospholipid digestion in the intestinal lumen is a prerequisite for efficient cholesterol absorption, additional enzyme(s) can compensate for pancreatic PLA2 in catalyzing phospholipid digestion and facilitating cholesterol absorption in PLA2 knockout mice.

Animals↗
PubMed2006

An atomic force microscope study of thermal behavior of phospholipid monolayers on mica.

We observed by using atomic force microscope (AFM) phospholipid (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) monolayers on mica being annealed and cooled to a selection of temperatures through steps of 2-4 degrees C/min. The annealed phospholipid monolayers started to disappear at 45-50 degrees C and disappeared completely above 60-63 degrees C under AFM observation. The phospholipid monolayers reformed when the samples were cooled below 60 degrees C and developed from fractal into compact monolayer films with decreasing temperatures. Simultaneously the height of the reformed phospholipid films also increased with decreasing temperatures from 0.4 nm to the value before annealing. The observed thermal features are attributed to a phase-transition process that upon heating to above 45-50 degrees C, the lipids condensed in the monolayers transform into a low-density expanded phase in which the lipids are invisible to AFM, and the transformation continues and completes at 60-63 degrees C. The lipid densities of the expanded phase inferred from the dissociated area of the condensed phase are observed to be a function of the temperature. The behavior contrasts with a conventional first-order phase transition commonly seen in the Langmuir films. The temperature-dependent height and shape of the reformed phospholipid films during cooling are argued to arise from the adjustment of the packing and molecular tilting (with respect to the mica surface) of the phospholipids in order to accommodate more condensed phospholipids.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2002

Nucleotides and phospholipids compete for binding to the C terminus of KATP channels.

Inwardly rectifying, ATP-sensitive K+ channels (K(ATP)) couple metabolism to either cell excitability (Kir6.x) or potassium secretion (Kir1.1). Phosphatidylinositol phospholipids, like PI(4,5)P2, antagonize nucleotide inhibition of K(ATP) channels enhancing the coupling of metabolic events to cell electrical or transport activity. The mechanism by which phospholipids relieve ATP block is unclear. We have shown that maltose-binding fusion proteins (MBP) containing the COOH termini of K(ATP) channels (Kir1.1, Kir6.1, and Kir6.2) form functional tetramers that directly bind at least two ATP molecules with negative cooperativity. Here we show that purified phosphatidylinositol phospholipids compete for 2,4,6,-trinitrophenyl (TNP)-ATP binding to the COOH termini of K(ATP) channels with EC50 values for PIP2 between 6-8 microM. The phospholipid potency profile was PIP3 > PIP2 = PIP > PI, suggesting that net phospholipid charge was important. A role for head group charge was supported by polycations (neomycin, spermine, and polylysine) reversing the effect of PIP2 on TNP-ATP binding to the Kir1.1 channel COOH terminal fusion protein. In contrast, the water-soluble charged hydrolytic product of PIP2, inositol(1,4,5)P3 (IP3), had no effect on TNP-ATP binding, suggesting that the acyl chain of PIP2 was also necessary for its effect on TNP-ATP binding. Indeed, neutral and charged lipids had weak, but significant, effects on TNP-ATP binding. Whereas microM concentrations of PIP2 could compete with TNP-ATP, we found that mM concentrations of MgATP were required to compete with PIP2 for binding to these K(ATP) channel COOH termini. Thus the COOH termini of K(ATP) channels form a nucleotide- and phospholipid-modulated channel gate on which ATP and phospholipids compete for binding.

Adenosine Triphosphate↗
PubMed1993

Insulin stimulates the biosynthesis of chiro-inositol-containing phospholipids in a rat fibroblast line expressing the human insulin receptor.

HIRc-B cells (rat fibroblasts expressing the human insulin receptor) were incubated with myo-[3H]inositol for 48 hr, and the biosynthesis of chiro-[3H]inositol was investigated in the absence and presence of insulin following a time course up to 60 min. After phase separation, treatment with insulin for 15 min caused a 2.2-fold increase in the specific radioactivity of chiro-[3H]inositol-containing phospholipids in contrast to a 1.2-fold increase in the specific radioactivity of myo-[3H]inositol-containing phospholipids. No insulin-mediated change in the specific radioactivity was observed in the inositol phosphates or free inositols. Further detailed analysis of individual [3H]inositol-containing phospholipids demonstrated marked increases in specific activity of the chiro-[3H]inositol phospholipids after 15 min of incubation with insulin: phosphatidylinositol 4-phosphate and 4,5-bisphosphate, 4.2-fold; lysophosphatidylinositol, 1.5-fold; phosphatidylinositol, 3.2-fold. In contrast, myo-[3H]inositol-containing phospholipids demonstrated relatively small increases (1.1- to 1.4-fold) after 5 min of incubation with insulin. These findings indicate that insulin stimulates de novo synthesis of chiro-inositol-containing phospholipids at the inositol phospholipid level.

Animals↗
PubMed1996

G protein-coupled receptor kinase GRK2 is a phospholipid-dependent enzyme that can be conditionally activated by G protein betagamma subunits.

G protein-coupled receptor kinases (GRKs) mediate agonist-dependent phosphorylation of G protein-coupled receptors (GPRs) and initiate homologous receptor desensitization. Previously, we reported that charged phospholipids directly interacted with the two GRK isoforms, GRK2 and GKR3, via a pleckstrin homology (PH) domain to regulate GRK activity (DebBurman, S. K., Ptasienski, J., Boetticher, E., Lomasney, J. W., Benovic, J. L., and Hosey, M. M. (1995) J. Biol. Chem. 270: 5742-5747). Here, evidence is provided to support the hypothesis that charged phospholipids are required for agonist-dependent phosphorylation of receptors by GRK2. In the absence of charged phospholipids, the purified human m2 muscarinic acetylcholine receptor (hm2mAChR) reconstituted in pure phosphatidylcholine vesicles or in a noninhibitory detergent was not a substrate for GRK2. However, these receptor preparations were stoichiometrically phosphorylated in an agonist-dependent manner upon addition of charged phospholipids. The known ability of G protein betagamma subunits to stimulate mAChR phosphorylation also was found to be absolutely dependent on the presence of charged phospholipids, including phosphatidylinositol 4,5-bisphosphate (PIP2). Phospholipids also regulated GRK-mediated phosphorylation of casein, a nonreceptor-soluble substrate. Among lipids tested, lipid inositol phosphates, PIP2 and phosphatidylinositol 4-monophosphate, were found to be the most potent activators of GRK2 and were the only lipids that regulated GRK2 in a complex biphasic manner. At low micro concentrations, PIP2 activated GRK2 via an interaction with the GRK pleckstrin homology domain; however, at high micro concentrations, PIP2 inhibited GRK2, apparently via another mechanism. PIP2-mediated inhibition could be partly relieved by increasing ATP. The results support the hypothesis that GRK2 is a lipid-dependent protein kinase that requires charged phospholipids for enzyme activation, for regulation by Gbetagamma subunits, and potentially for membrane association.

Adenosine Triphosphate↗
PubMed2001

Caenorhabditis elegans PIAK, a phospholipid-independent kinase that activates the AKT/PKB survival kinase.

Phospholipid-dependent kinase 1 (PDK 1) is a 3'-phospholipid-responsive serine/threonine kinase that plays a critical role in cell survival by phosphorylating and activating the anti-apoptotic AKT/PKB kinase. While PDK 1 is clearly an important component of the cell survival machinery, the potential for phospholipid-independent activation of the AKT/PKB survival pathway has not been extensively examined at the molecular level. We have identified a second form of PDK 1 in the nematode Caenorhabditis elegans that we have termed PIAK (phospholipid-independent AKT/PKB kinase). PIAK is highly homologous to C. elegans and mammalian PDK 1 with the exception that the novel kinase lacks a phospholipid binding pleckstrin homology domain. The domain structure of PIAK suggests that it might be a phospholipid-independent kinase, and PIAK phosphorylates mammalian AKT/PKB at the activating Thr(308) residue in the presence of the phosphatidylinositol (PI) 3-kinase inhibitors as well as in the absence of growth factors. In addition, PIAK is capable of inducing the phospholipid-independent, AKT/PKB-induced phosphorylation of the AFX-type forkhead transcription factor, resulting in its cytoplasmic localization. Because the nuclear localization of this transcription factor induces an apoptotic state, this PIAK-mediated cytoplasmic sequestration allows for cell survival. Finally, PIAK activity appears to be induced by various inhibitors of cell cycle G(1) progression. These data suggest an alternate, phosphatidylinositol 3-kinase-independent mechanism for the activation of the AKT/PKB survival pathway that may be utilized during periods of cellular quiescence.

Amino Acid Sequence↗
PubMed2000

Surfactant phospholipids and surface activity among preterm infants with respiratory distress syndrome who develop bronchopulmonary dysplasia.

Our objective was to determine if preterm infants with respiratory distress syndrome who develop bronchopulmonary dysplasia have abnormalities in surfactant phospholipids and/or function. Tracheal aspirate samples obtained from preterm infants with respiratory distress syndrome on days 1, 3-5, 7-10, 14-17, 21-24 and 27-30 were analyzed for total phospholipids and phospholipids fractions by determination of total phospholipid phosphorus and thin layer chromatography, respectively. Surfactant properties were assessed with captive bubble surfactometer. Sixteen out of 56 (29%) infants died during the first 30 d of life. Infants who died were more immature, required more ventilatory support and had a surfactant with lower surface-tension-reducing properties than infants who survived (p < 0.05). Surviving infants were divided into group I (no bronchopulmonary dysplasia at 27-30 d, n = 25) and group II (with bronchopulmonary dysplasia at 27-30 d, n = 15). No significant differences in concentrations of surfactant phospholipids nor measurements of surface tension were noted among groups of infants. Surfactant therapy after birth was associated with a significant increase in concentrations of total phospholipids, lecithin, phosphatidylinositol and lower surface-tension measurements at 3-5 d of age among surviving infants (p < 0.01). Abnormalities in concentrations of surfactant phospholipids or surfactant function could not be demonstrated during the first month of life among preterm infants with respiratory distress syndrome who develop bronchopulmonary dysplasia.

Bronchopulmonary Dysplasia↗
PubMed1981

Alterations of new methylated phospholipid synthesis in the plasma membranes of macrophages exposed to chemoattractants.

Chemotactic factors have been shown to inhibit the methylation of phosphatidylethanolamine in macrophages without affecting total phospholipid synthesis. It would thus be anticipated that newly synthesized membranes of macrophages exposed to chemoattractants would have an increased ratio of phosphatidylethanolamine to its methylated derivatives. These ratios were measured directly in newly synthesized phospholipids of plasma membranes isolated from guinea pig peritoneal macrophages. The phosphatidylethanolamine: methylated phospholipid ratio in such plasma membranes was increased by 53 to 111% upon exposure of the cells to chemotactic factors. This increase was due to decreased synthesis of methylated phospholipids and not to altered formation of phosphatidylethanolamine or activation of phospholipases. Methylated phospholipid ratios were also studied in the leading front lamellipodia isolated from macrophages migrating under chemotactic and nonchemotactic conditions. The phosphatidylethanolamine:methylated phospholipid ratios were increased up to fourfold in lamellipodia of macrophages migrating towards chemotactic agents when compared to those from cells migrating randomly. Biophysical changes in the plasma membrane produced by an increase in the ratio of phosphatidylethanolamine:methylated phospholipids as a result of exposure of cells to chemoattractants may be required for sustained directed migration.

Animals↗
PubMed1986

Mechanism of phorbol ester activation of calcium-activated, phospholipid-dependent protein kinase.

Tumor-promoting phorbol esters activated a calcium-activated, phospholipid-dependent protein kinase by direct complexation with this protein kinase and phospholipid in the presence of divalent cations and this complexation was identical to association of kinase/receptor activity with cell membranes. Treatment of isolated mouse spleen lymphocytes with phorbol ester tumor promoters resulted in a rapid shift in the subcellular localization of both the phorbol ester receptor and a calcium-activated, phospholipid-dependent protein kinase activity. Both activities shifted from almost entirely soluble to largely membrane-associated, which is consistent with a single protein possessing both activities. Activation of partially purified kinase/receptor activity by phorbol ester or calcium alone or in combination occurred in parallel to the formation of a complex between the kinase/receptor and phospholipid. Magnesium also was important both for complex formation and for activation of the protein kinase. Although phorbol ester did not appear to affect the affinity of the kinase/receptor for phospholipid, it did increase the extent of formation of a stable complex between the receptor and the phospholipid. These observations support the hypothesis that the cell membrane is the locus of action of both the phorbol esters and the calcium-activated, phospholipid-dependent protein kinase activity.

Animals↗
PubMed1971

Phospholipids in the Uredospores of Uromyces phaseoli: I. Identification and Localization.

Utilizing paper, thin layer and gas chromatography, the phospholipids of dormant and germinating spores have been isolated and identified. The identifications were based upon agreements of retardation factor values between the unknowns and reference compounds and their derivatives. Quantitative analysis of components, color reactions and specific labeling experiments were also used to support certain identifications. At least three, and usually more, criteria were used for each phospholipid that was definitively identified.The major phospholipids of Uromyces phaseoli are phosphatidylcholine and phosphatidylethanolamine. Diphosphatidylglycerol, or cardiolipin, phosphatidylinositol, and another phosphoinositide were present as minor components. In germinating spores, phosphatidylmonomethylethanolamine, phosphatidyldimethylethanolamine, phosphatidylserine, and phosphatidic acid were detected in trace amounts. The presence of these common intermediates in the biosynthesis of phospholipids indicates that phospholipid synthesis is active during the germination process. Except for the absence of phosphatidylglycerol, the types of phospholipids present are similar to the host plant. Germ tube wall preparations were found to contain phosphatidylcholine and phosphatidylethanolamine in about the same proportion as that observed in resting spores, while the proportion of diphosphatidylglycerol was about three times higher. An unidentified phosphorous-containing lipid was also a significant component of the total phospholipids extracted from germ tube walls.

Journal Article↗