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At least 19 recordsLinked to original sources
PubMed1979

Fusion of phosphatidylserine and mixed phosphatidylserine-phosphatidylcholine vesicles. Dependence on calcium concentration and temperature.

Dynamic light scattering has been used to study the temperature dependence of Ca2+-induced fusion of phosphatidylserine vesicles and mixed vesicles containing phosphatidylserine and different phosphatidylcholines. The final vesicle size after Ca2+ and EDTA incubation serves as a measure of the extent of fusion. With phosphatidylserine vesicles, the extent of fusion shows a sharp maximum at an incubation temperature which depends on the Ca2+ concentration between 0.8 and 2 mM. The shift in the fusion peak temperature with Ca2+ concentration is similar to the typical shift in the phase transition temperature with divalent cation concentration in acidic phospholipids. The results suggest a direct correlation between the fusion peak temperature and the phase transition temperature in the presence of Ca2+ prior to fusion. With mixed vesicles containing up to 33% of a phosphatidylcholine in at least 2 mM Ca2+, the extent of fusion as a function of incubation temperature also shows a maximum. The fusion peak temperature is essentially independent of the quantity and type of phosphatidylcholine and the Ca2+ concentration, and identical to that with pure phosphatidylserine in excess Ca2+. The results imply that Ca2+- induced molecular segregation occurs first, and fusion subsequently takes place between pure phosphatidylserine domains.

Calcium↗
PubMed1975

Synthesis of a new phosphatidylserine spin-label and calcium-induced lateral phase separation in phosphatidylserine-phosphatidylcholine membranes.

A new phosphatidylserine spin label with nitroxide stearate attached at the 2 position has been synthesized by the reaction of spin-labeled CDP-diglyceride with L-serine under the catalytic action of phosphatidylserine synthetase. Some structural properties of pure phosphatidylserine (PS) and binary PS-phosphatidylcholine (PC) membranes were studied with the spin label. PS membrane became solidified on lowering solution pH, 50% solidification being attained at pH 3.5. The membrane was also solidified by addition of Ca-2+. The effect of Ba-2+,Sr-2+, and Mg-2+ was smaller than that of Ca-2+. The calcium-induced lateral phase separation in the binary membrane was studied from the side of the calcium-receiving lipid. The results confirmed and extended our previous conclusion drawn with PC spin label. The phase diagram of the binary membrane in the presence of Ca-2+ was determined. Not all PS molecules were aggregated to form the solid patches but some remained dissolved in the fluid PC matrix. The fluid PS fraction was larger for the membranes containing more PC. The membrane with 10% PS still had a significant fraction of solid phase. The rate of calcium-induced aggregation was greatly dependent on the PS content. The aggregation was almost complete within 5 min in the membrane containing 67% PS, while it was still proceeding after several hours in the membrane with 20% PS. The rate-limiting step was suggested to be in the formation of "stable" nuclei consisting of larger aggregates. The possible biological significance of the ionotropic phase separation was discussed whereby a transient density fluctuation was emphasized.

Barium↗
PubMed1976

Conditional lethal phosphatidylserine decarboxylase mutants of Escherichia coli. Mapping of the structural gene for phosphatidylserine decarboxylase.

The final step in the biosynthesis of phosphatidylethanolamine, the major membrane lipid of Escherichia coli, is catalyzed by the membrane-bound enzyme, phosphatidylserine decarboxylase. A variation of a procedure for localized mutagenesis (Hong and Ames, 1971) was employed to generate conditional lethal mutants in phosphatidylserine decarboxylase. In our modification, an episome carrying the psd gene closely linked to purA+ was heavily mutagenized in vivo in a strain also lysogenic for phage P1CMclr100. After induction of a phage lytic cycle, the purA+ marker was transduced to a purA- recipient. A majority of the Pur+ transductants thus contained a psd gene originating from the heavily mutagenized episomal strain. Three mutants were isolated in which temperature-sensitive growth is caused by thermosensitive phosphatidylserine decarboxylase activity that is defective in vivo at the non-permissive temperature. All 3 mutations were mapped at the same location as psd1, being cotransduced with melA, purA, and ampA. The gene order in this region, as determined by a phage Pl-meidated, three-factor cross is ampA-psd-purA. psd+ is dominant to the psd mutant alleles.

Alleles↗
PubMed1979

Activation of human brain galactosylceramidase by phosphatidylserine.

Assays of sphingolipid hydrolases in vitro generally require bile salts or other detergents. A few 'activator proteins' have been reported that can partially replace the detergents in the assay mixture. We report here that phosphatidylserine from bovine brain is a relatively specific activator of human brain galactosylceramidase in the absence of sodium taurocholate (phosphatidylserine system). Activity similar to that obtained with the conventional assay system containing taurocholate and oleic acid (taurocholate system) could be obtained. Other lipids tested generally gave less than 10% of the taurocholate system activity, but sulfatide could activate human brain galactosylceramidase to 20--30% of the taurocholate system. The properties of the reaction in the phosphatidylserine system were examined with human brain whole homogenate, crude soluble post-concanavalin A preparations, and partially purified preparations as the enzyme source and compared with those obtained with the taurocholate system. The pH optimum shifted from 4.2 in the taurocholate system to 4.7 in the phosphatidylserine system. The phosphatidylserine system was superior in the linearity of the reaction with respect to the enzyme protein. Reasonably linear Lineweaver-Burk plots could be obtained. The Km values for the phosphatidylserine system were greater than those for the taurocholate system. The effect of phosphatidylserine was not additive to that of taurocholate. Additional phosphatidylserine to the taurocholate system was either without effect at lower concentrations or inhibitory at higher concentrations. The assays of galactosylceramidase with phosphatidylserine and without taurocholate do not necessarily provide pragmatic advantages but offer a potentially useful system with which to study the mechanism of in vivo degradation of the membrane-bound glycosphingolipid.

Brain↗
PubMed1978

Phospholipid changes in synaptic membranes by lipolytic enzymes and subsequent restoration of opiate binding with phosphatidylserine.

A study has been made of the role of phosphatidylserine in stereospecific opiate binding to neural membranes, utilizing specific lipolytic enzymes to attack the lipid. At very low concentrations phospholipase A2 from bee venom will preferentially hydrolyze C22:6-fatty acid; and even after a few percent of the total phosphatidylserine is hydrolyzed, opiate binding is greatly inhibited. The addition of brain phosphatidylserine will restore opiate binding; however, when the inhibition approaches 50% restoration is only partial. Exposure of membranes to phosphatidylserine decarboxylase will partially inhibit opiate binding; and the binding returns to the control level after the addition of phosphatidylserine. The partial inhibition of opiate binding by low concentrations of Triton X-100, which presumably remove lipids, can be partially reversed by phosphatidylserine. The binding of 3H-naloxone, an opiate antagonist, is similar to agonists in its behavior towards phospholipases and phosphatidylserine; however, binding of naltrexone, also an antagonist, is far less responsive. It is concluded that the phosphatidylserine associated with the opiate receptor is the C18:0, 22:6-diacyl form, which is closely associated with protein.

Animals↗
PubMed1979

Pharmacological effects of phosphatidylserine liposomes: the role of lysophosphatidylserine.

1. Unique among the phospholipids, phosphatidylserine depresses brain energy metabolism when injected intravenously into mice in the form of sonicated liposomes. The possibility that this effect results from a metabolic transformation of phosphatidylserine is examined in this paper. 2. A strong enhancement of the phosphatidylserine effect is induced by the incubation of liposomes with rat serum. Similar phosphatidylserine activation is observed after the incubation of the phospholipid with purified phospholipase A2 from pancreas. In both cases phosphatidylserine is split into the deacylated derivative, lysophosphatidylserine. 3. Lysophosphatidylserine reproduces with greater efficacy the effect of phosphatidylserine on brain energy metabolism. Other lysophospholipids are not effective. 4. It is concluded that the pharmacological effects of phosphatidylserine liposomes is due to the generation of lysophosphatidylserine.

Animals↗
PubMed1977

Enhancement of opiate binding by various molecular forms of phosphatidylserine and inhibition by other unsaturated lipids.

A study was undertaken on the possible involvement of phospholipids on stereospecific opiate binding to a rat brain membrane fraction comprised mainly of synaptic membranes. The addition of acidic phospholipids such as phosphatidylserine, phosphoinositides, and phosphatidic acid significantly enhanced opiate binding. With the exception of phosphatidylserine, when the acidic phospholipids contained a polyunsaturated acyl group, they were actually inhibitory, along with neutral phospholipids derived from brain. Both the C18:0, C18:1 form (derived from myelin) and the C18:0, C22:6 form of phosphatidylserine (derived from synaptic membranes) produced as much as a 45% enhancement in opiate binding. Unsaturated fatty acids were highly inhibitory, the degree of inhibition being related to the degree of unsaturation. Both phospholipase A and C were inhibitory; and the inhibitory effect of A could not be prevented by albumin or overcome with the addition of phosphatidylserine. With the use of the cross-linking agent, dinitrodifluorobenzene, it could be demonstrated that the phosphatidylserine of synaptic membranes appeared to be preferentially associated with membrane protein. The enhancement of opiate binding by phosphatidylserine diminished with increasing degree of cross-linking.

Animals↗
PubMed1979

The interaction of spectrin-actin and synthetic phospholipids. II. The interaction with phosphatidylserine.

Sonicated vesicles of phosphatidylserine and phosphatidylserine/phosphatidylcholine mixtures were recombined with spectrin-actin from human erythrocyte ghosts. Morphological properties and physicochemical characteristics of the recombinates were studied with freeze etch electron microscopy, 31P NMR and differential scanning calorimetry. Sonicated dimyristoyl phosphatidylserine vesicles show a decrease in enthalpy change of the lipid phase transition upon addition of spectrin-actin. These vesicles collapse and fuse, into multilamellar structures in the presence of spectrin-actin, as demonstrated by freeze fracturing and NMR. Spectrin-actin cannot prevent the salt formation between phosphatidylserine and Ca2+, all phosphatidylserine is withdrawn from the lipid phase transition. In contrast a protection against the action of Mg2+ could be observed. Mixed bilayers of dimyristoyl phosphatidylserine/dimyristoyl phosphatidylcholine show phase separations at molar ratios above 1/1 (van Dijck, P.W.M., de Kruijff, B., Verkleij, A.J., van Deenen, L.L.M. and de Gier, J. (1978) Biochim. Biophys. Acta 512, 84--96). These phase spearations can be prevented by spectrin-actin. Ca2+-induced lateral phase separations in cocrystallizing phosphatidylserine/phosphatidylcholine mixtures, can be reduced by spectrin-actin. Formation of the Ca2+-phosphatidylserine salt, occurring in addition to lateral phase separation when mixtures contain more than 30 mol % phosphatidylserine, cannot be prevented by spectrin-actin.

Actins↗
PubMed1975

Silica gel thin-layer chromatography of acidic phospholipids. II. Chromatographic behaviour of phosphatidylserine and phosphatidic acid applied with different cation composition on adsorbents either free of metal ions or containing a surplus of divalent metal ions.

Different salt forms of phosphatidylserine and phosphatidic acid (two acidic phospholipids) have been subjected to thin-layer chromatography on two commonly used silica adsorbents, one of which (silica gel HR) is practically free of metal ions and the other (silica gel G) contains 13% of calcium sulphate as binder. The chromatographic behaviour was studied in an acidic, a neutral and a basic solvent. Both adsorbents provided usable systems for phosphatidylserine with each of the three solvents, except for silica gel G with the neutral solvent, in which system tailing was prominent. The inclusion of calcium sulphate in the silica gel tended to impair chromatography of phosphatidylserine in acidic and neutral solvents, but improved its chromatography in the basic solvent. In all the systems, the migration was independent of the cation composition of the applied phosphatidylserine samples. For the chromatography of phosphatidic acid, only three of the systems tested were usable, and in those three, the chromatographic behaviour was independent of the cation composition of the samples. The calcium sulphate in an adsorbent increased tailing of phosphatidic acid in acidic and neutral solvents, as it did for phosphatidylserine, whereas with the basic solvent, calcium sulphate in the adsorbent caused phosphatidic acid to remain at the origin. Two one-dimensional thin-layer chromatographic systems previously recommended for the chromatography of acidic phospholipids were unsuitable for the chromatography of phosphatidic acid under the conditions used here. For both phosphatidylserine and phosphatidic acid chromatographed in acidic systems, the solvent must contain water in addition to acetic acid if excessive tailing is to be avoided.

Calcium↗
PubMed1979

Inhibition of mast cell histamine secretion by N-substituteed derivatives of phosphatidylserine.

The structural basis for the highly specific action of phosphatidylserine in enhancing mast cell histamine secretion induced by concanavalin A was investigated by studying the activities of three N-substituted derivatives: N-acetyl phosphatidylserine, N-1-dimethylaminonaphthalene-5-sulfonly phosphatidylserine, and N-4-nitrobenzo-2-oxa-1,3-diazole phosphatidylserine. None of the derivatives was capable of activating concanavalin A-induced histamine secretion at concentrations two to three times that required for maximal activation by phosphatidylserine. Instead, the derivatives were found to inhibit the secretory response of mast cells to the calcium ionophore A23187 as well as to concanavalin A. The inhibition was noncytotoxic, partially reversible by washing, and associated with binding of N-substituted phosphatidylserine to the mast cell.

Animals↗
PubMed1978

[Effect of phosphatidylserine in hemocoagulating action of factors V, VII and autoprothrombin C].

It was found that phosphatidylserine inhibits the activating effect of factors V, VII and autoprothrombin C on the thromboplastin time of plasma. This is in agreement with the previously observed phosphatidylserine ability to form an inactive complex with the substrate of thrombinogenesis, i.e. prothrombin. The excess of autoprothrombin C results in changes in the kinetic parameters of the inhibiting effect of phosphatidylserine on the thrombinogenesis, which is indicative of the interaction between autoprothrombin C and phosphatidylserine. Data from gel-filtration on Sephadex G-100 and differential spectrophotometry support the evidence for the formation of the autoprothrombin C-phosphatidylserine complex. During ion-exchange chromatography and gel-filtration the autoprothrombin C preparations are eluted as an acute symmetrical peak; using electrophoresis in agarose gel, two fractions were revealed in the preparations. The first fraction migrates with gamma-globulins, whereas the second one--with alpha-globulins. The presence of phosphatidylserine in the autoprothrombin C solution does not change its migration rate during electrophoresis.

Blood Coagulation↗
PubMed1979

Complex phase mixing of phosphatidylcholine and phosphatidylserine in multilamellar membrane vesicles.

The phase mixing in dipalmitoyl phosphatidylcholine and bovine brain phosphatidylserine mixtures suspended in aqueous salt solutions was studied by differential scanning calorimetry, freeze-fracture electron microscopy and X-ray and electron diffraction. The pure dipalmitoyl phosphatidylcholine has two well-defined solidus phases P beta' and L beta' and a liquidus phase L alpha while the pure phosphatidylserine has a broad transition from L beta to L alpha. The mixture exhibits some dipalmitoyl phosphatidylcholine characteristics up to 30% phosphatidylserine when pure P beta' phase no longer exists. Phase mixing is observed at all compositions. An addition of 3% phosphatidylserine is found to be sufficient to destroy the sharp L beta'--P beta' transition observed in pure dipalmitoyl phosphatidylcholine. The transition between L beta' and P beta' in these mixtures is displaced to lower temperatures and becomes gradual as depicted by all three techniques, but freeze-fracture gives more definite information of the continuous transition. The most striking observation on the morphology of the mixed membranes (3--30% phosphatidylserine in dipalmitoyl phosphatidylcholine) is the presence of banded patterns (P beta') at temperatures well below the main transition peak as detected by differential scanning calorimetry.

Calorimetry, Differential Scanning↗
PubMed1976

Ion-binding to phospholipids. Interaction of calcium with phosphatidylserine.

The binding of Ca2+ to monolayers and bilayers of phosphatidylserine has been investigated as a function of pH, ionic strength (NaCl concentration) and Ca2+ concentration using surface and colloid chemical techniques. The molar ratio of lipid to bound calcium decreases to 2 as the Ca2+ concentration is increased to about 0.1 mM. At [Ca2+] greater than 0.1 mM a 1:1 complex is formed. The apparent binding constant Ka ranges from about approximately 10(6) - 10(4) l/mol depending on the Ca2+ concentration. After allowing for electrostatic effects and neighbour group interactions, the intrinsic binding constant Ki of the phosphorylserine polar group at pH 7 (I = 0.01 M), where it carries a net negative charge of one, is approximately 10(4) l/mol; consistent values for Ki were obtained using several independent approaches. Ka for Ca2+ binding decreases with increasing NaCl concentration because the monovalent cations compete with Ca2+ for the same binding site. Na+ and K+ are equally effective in displacing 45Ca2+ adsorbed to monolayers of phosphatidylserine, both with respect to the kinetics and the equilibrium of the displacement. Ka for the reaction between phosphatidylserine and monovalent cations is about 10(3)-fold smaller than that of Ca2+. An investigation of the binding of Mn2+ to phosphatidylserine by both surface chemical and nuclear magnetic resonance methods shows that this cation has a similar binding constant to that of Ca2+. The Ca2+-binding capabilities of monolayers containing only carboxyl groups (i.e. arachidic acid) and phosphodiester groups (i.e. dicetyl phosphate) have also been determined; the apparent pK for the - COOH group in monolayers is larger than or equal to 9 and that for the phosphodiester group is less than 4. Since these groups do not retain the same pK values when they are in close proximity in the phosphorylserine group, the relative contributions of the two groups to the binding of Ca2+ to phosphatidylserine is not obvious.

Binding Sites↗
PubMed1978

Phospholipid composition and membrane function in phosphatidylserine decarboxylase mutants of Escherichia coli.

Temperature-sensitive conditional lethal mutants in phosphatidylserine decarboxylase (psd) accumulate large amounts of phosphatidylserine under nonpermissive conditions (42 degrees C) prior to cell death. In addition, the ratio of cardiolipin to phosphatidylglycerol is increased. At an intermediate temperature (37 degrees C), high levels of phosphatidylserine can be maintained with little effect on cell growth or viability. Under these conditions, both the rate of induction and the function of the lactose transport system are normal. At 42 degrees C addition of Mg2+ or Ca2+ to mutant cultures produces a partial phenotypic suppression. Growth is prolonged and the filaments normally present at 42 degrees C do not form. Upon transfer to the nonpermissive temperature, there is a considerable lag before accumulation of phosphatidylserine begins and the growth rate is affected. Based on the kinetics of heat inactivation of phosphatidylserine decarboxylase activity in extracts, in intact nongrowing cells, and in growing cells, it appears that the enzyme newly synthesized at 42 degrees C is more thermolabile in vivo than enzyme molecules previously inserted into the membrane at the lower temperature. Thus, the older, stable enzymatic activity must be diluted during growth before physiological effects are observed.

Calcium↗
PubMed1978

Surface potential of phosphatidylserine monolayers. I. Divalent ion binding effect.

Surface potentials of phosphatidylserine monolayers have been measured in the presence of different divalent ion concentrations in order to determine the way in which divalent ions bind to the membrane surface. The association constants for divalent ions (Mg2+, Ca2+ and Mn2+) with the phosphatidylserine membrane have been obtained from the experimental data and simple ion binding theory. The order of divalent ion binding to the membrane is Mn2+ greater than Ca2+ greater than Mg2+. However, none of the divalent ions used completely neutralized the negative charge of phosphatidylserine even at relatively high concentrations. The amounts of the divalent ions bound depended upon the concentration of the monovalent ions present in the subphase. It is suggested that the amounts of bound ions obtained from the use of radioisotope tracer methods may include a considerable contribution from the excess free ions in the double layer region of the phosphatidylserine membrane.

Binding Sites↗
PubMed1978

Specificity of Ca2+ and Mg2+ binding to phosphatidylserine vesicles and resultant phase changes of bilayer membrane structure.

Differences in the interaction of Ca2+ and Mg2+ with phosphatidylserine vesicles were revealed by binding studies, differential scanning calorimetry and X-ray diffraction. The two cations produced structurally different complexes with phosphatidylserine as evidenced by phase transition characteristics, lamellar spacings, and hydrocarbon packing. Ca2+ effectively completes with Mg2+ for phosphatidylserine binding sites. Analysis of the binding data showed that Ca2+ had a ten-fold greater intrinsic binding constant for phosphatidylserine.

Binding Sites↗
PubMed1979

Specificity of Na+ binding to phosphatidylserine vesicles from a 23Na NMR relaxation rate study.

23Na NMR relaxation rate measurements show that Na+ binds specifically to phosphatidylserine vesicles and is displaced partially from the binding site by K+ and Ca2+ but to a considerably less extent by tetraethylammonium ion. The data indicate that tetraethylammonium ion affects the binding of Na+ only slightly, by affecting the surface potential through its presence in the double layer, without competing for a phosphatidylserine binding site. Values for the intrinsic binding constant for the Na+-phosphatidylserine complex that would be consistent with the competition experiments (and the dependence of the relaxation rate on concentration of free Na+) fall in the range 0.4--1.2 M-1 with a better fit towards the higher values. We conclude that in the absence of competing cations in solution an appreciable fraction of the phosphatidylserine sites could be associated with bound Na+ at 0.1 M Na+ concentration.

Calcium↗