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PubMed2001

Interaction of GM(1) glycolipid in phospholipid monolayers with wheat germ agglutinin: effect of phospholipidic environment and subphase.

Mixed monolayers of GM(1) glycolipid and stearoyl-oleoyl-phosphatidylcholine (SOPC) or dipalmitoyl-phosphatidycholine (DPPC) phospholipids were studied by surface pressure measurements. The effects induced by GM(1) on the mean molecular areas of mixtures and DPPC phase transition were followed for GM(1) concentrations ranging from 1 to 20 mol.%. Under our experimental conditions, one main parameter influencing the behavior of phospholipid-GM(1) monolayers is the ionic strength of the subphase. Mixed monolayers are in a more expanded state on buffer than on pure water. This could be due to a change of GM(1) orientation at the interface. The interaction of wheat germ agglutinin (WGA), a lectin recognizing specifically GM(1), with these monolayers was quantified in terms of the Gibbs equation. Specific WGA-GM(1) interactions are clearly reduced in the presence of DPPC as compared with SOPC, probably because of the higher packing density of these monolayers. Phospholipid-GM(1) monolayers could also undergo some rearrangements induced by WGA binding.

Binding Sites↗
PubMed1983

Reincorporation of adenosine 5'-diphosphate/adenosine 5'-triphosphate carrier into phospholipid membranes. Phospholipid-protein interaction as studied by phosphorus-31 nuclear magnetic resonance and electron microscopy.

Combined phosphorus-31 nuclear magnetic resonance (31P NMR) and electron microscopic studies were performed on the ADP/ATP carrier protein from beef heart mitochondria. The protein was incorporated into phospholipids by addition of Triton-protein micelles to a lipid suspension or to the dry lipid. All of the phospholipid (egg phosphatidylcholine or mixtures of egg phosphatidylcholine and egg phosphatidylethanolamine) that contributed to the observed 31P NMR signal under these conditions appeared to be in a bilayer configuration. Freeze-fracturing and negative-staining electron microscopy showed unilamellar vesicles and multilayers. An isotropic signal could be attributed to vesicle rotation, judging from its sensitivity to increasing viscosity. The presence of small vesicles was also noticeable in the 31P NMR spectra of planar oriented membranes. In the presence of phosphatidylethanolamine, aggregation of protein particles was observed. Gel chromatography of the protein-Triton-phospholipid mixture revealed that, before Triton removal, large amounts of protein are associated with multibilayers. Separation of loaded and unloaded membranes by centrifugation in D2O showed that, upon stepwise addition, protein incorporates preferentially into unloaded liposomes. From these findings a mechanism of protein reincorporation was deduced.

Animals↗
PubMed2006

Phospholipid hydroxyalkenals, a subset of recently discovered endogenous CD36 ligands, spontaneously generate novel furan-containing phospholipids lacking CD36 binding activity in vivo.

We recently identified a novel family of oxidized choline glycerophospholipid (oxPC) molecular species enriched in atheroma that serve as endogenous ligands for the scavenger receptor CD36 (oxPC(CD36)), facilitating macrophage cholesterol accumulation and foam cell formation (Podrez, E. A., Poliakov, E., Shen, Z., et al. (2002) J. Biol. Chem. 277, 38517-38523). A high affinity CD36 recognition motif was defined within oxPC(CD36), an oxidatively truncated sn-2 acyl group with a terminal gamma-hydroxy (or oxo)-alpha,beta-unsaturated carbonyl. The fate of these species once formed in vivo is unknown. Here we show that a subset of oxPC(CD36), a phosphatidylcholine molecular species possessing sn-2 esterified fatty acyl hydroxyalkenal groups, can undergo a slow intramolecular cyclization and dehydration reaction to form novel oxPC species possessing a sn-2 acyl group that incorporates a terminal furyl moiety (oxPC-furan). Using high performance liquid chromatography with on-line tandem mass spectrometry in combination with unambiguous organic synthesis, we confirm that oxPC-furans, ultimately derived from phospholipids with sn-2 esterified docosahexaenoic, arachidonic, or linoleic acids, are formed during exposure of model membranes and isolated lipoproteins to physiological oxidant systems. In vivo generation of oxPC-furans at sites of enhanced oxidant stress is also demonstrated, such as within brain tissues following cerebral ischemia. Cell binding studies reveal that in contrast to their oxPC(CD36) precursors, oxPC-furans lack CD36 binding activity. Taken together, the present studies identify oxPC-furans as a novel family of oxidized phospholipids that are formed in vivo from phospholipid hydroxyalkenals but that lack CD36 binding activity.

Aldehydes↗
PubMed1980

Net transfer of phospholipid by the nonspecific phospholipid transfer proteins from bovine liver.

The nonspecific phospholipid transfer proteins from bovine liver catalyze net transfer of phosphatidylcholine and phosphatidylinositol from phosphatidylcholine/phosphatidylinositol multilamellar vesicles (9 : 1; mol/mol) to either intact or totally delipidated human high density lipoprotein. Under indentical conditions, the phosphatidylcholine-specific exchange protein from bovine liver and the phosphatidylinositol/phosphatidylcholine exchange protein from beef heart do not enhance the net transfer of labeled phosphatidylcholine or phosphatidylinositol from multilamellar vesicles to delipidated high density lipoprotein, but do catalyze phospholipid exchange between multilamellar vesicles and intact high density lipoprotein consistent with their reported specificities. In the presence of nonspecific transfer proteins net transfer of mass in also observed from phosphatidylcholine unilamellar vesicles to rat liver inner mitochondrial membranes plus matrix. These are the first exchange proteins demonstrated to have net mass transfer capability.

Animals↗
PubMed2005

Electron paramagnetic resonance studies of magnetically aligned phospholipid bilayers utilizing a phospholipid spin label: the effect of cholesterol.

X-band EPR spectroscopy has been employed to study the dynamic properties of magnetically aligned phospholipid bilayers (bicelles) utilizing a variety of phosphocholine spin labels (n-PCSL) as a function of cholesterol content. The utilization of both perpendicular and parallel aligned bicelles in EPR spectroscopy provides a more detailed structural and orientational picture of the phospholipid bilayers. The magnetically aligned EPR spectra of the bicelles and the hyperfine splitting values reveal that the addition of cholesterol increases the phase transition temperature and alignment temperature of the DMPC/DHPC bicelles. The corresponding molecular order parameter, Smol, of the DMPC/DHPC bicelles increased upon addition of cholesterol. Cholesterol also decreased the rotational motion and increased the degree of anisotropy in the interior region of the bicelles. This report reveals that the dynamic properties of DMPC/DHPC bicelles agree well with other model membrane systems and that the magnetically aligned bicelles are an excellent model membrane system.

Cholesterol↗
PubMed1999

Characterization and expression of the cDNA encoding a new kind of phospholipid transfer protein, the phosphatidylglycerol/phosphatidylinositol transfer protein from Aspergillus oryzae: evidence of a putative membrane targeted phospholipid transfer protein in fungi.

The full-length cDNA of a phospholipid transfer protein (PLTP) was isolated from Aspergillus oryzae by a RACE-PCR procedure using degenerated primer pool selected from the N-terminal sequence of the purified phosphatidylinositol/phosphatidylglycerol transfer protein (PG/PI-TP). The cDNA encodes a 173 amino acid protein of 18823 Da. The deduced amino acid sequence from position 38 to 67 is 100% identical to the N-terminal sequence (first 30 amino acids) of the purified PG/PI-TP. This amino acid sequence is preceded by a leader peptide of 37 amino acids which is predicted to be composed of a signal peptide of 21 amino acids followed by an extra-sequence of 16 amino acids, or a membrane anchor protein signal (amino acid 5-29). This strongly suggests that the PG/PI-TP is a targeted protein. The deduced mature protein is 138 amino acids long with a predicted molecular mass of 14933 Da. Comparison of the deduced PG/PI-TP sequence with other polypeptide sequences available in databases revealed a homology with a protein deduced from an open reading frame coding for an unknown protein in Saccharomyces cerevisiae (36% identity and 57% similarity). Apart from this homology, the PG/PI-TP is unique and specific to the filamentous fungi on the basis of comparison of PLTP protein sequences. Northern blot analysis of RNA isolated from A. oryzae cultures grown on glucose or glucose supplemented with phospholipids suggests that the PG/PI-TP is transcribed by only one RNA species and allows us to show that expression of the protein is regulated at the messenger RNA level.

Amino Acid Sequence↗
PubMed2000

Mechanism of the phospholipid transfer protein-mediated transfer of phospholipids from model lipid vesicles to high density lipoproteins.

To study the effects of the phospholipid transfer protein (PLTP) on the thermodynamic parameters governing the transfer of phospholipids (PL) from single bilayer vesicles (SBV) to high density lipoprotein (HDL), we performed transfer measurements at various temperatures between 4 and 65 degrees C, using a pyrenylphosphatidylcholine (Pyr-PC) as probe. The proportion of excimer (E) to monomer (M) fluorescence of a pyrenyl moiety constitutes a direct measure of its local concentration. The transfers of Pyr-PC were monitored by following the decrease of E/M. The data were used to calculate the rate constants K(+1) for the transfer from SBV to HDL and to generate the corresponding Arrhenius plots. The equilibrium constants, K(eq), for the same reactions were also determined and used to generate Van't Hoff plots. From these data, we calculated the thermodynamic parameters for both the whole transfer reaction and the transition state. Both K(+1) and K(eq) values clearly varied with temperature. PLTP induced very similar decreases in the free energy for the whole reaction (DeltaG) and in that for the transition state (DeltaG(#)). At 37 degrees C, the decreases were of 0.37 and 0.29 kcal/mol, respectively. We studied the thermal denaturation of PLTP between 37 and 65 degrees C, and the effects of denatured PLTP samples on the PL transfer reaction were then determined. In all cases, the changes of DeltaG remained comparable to those of DeltaG(#). Thus the essential action of PLTP is to facilitate the first step of the reaction, which can be considered as the desorption of PL molecules from the surface of donor particles.

Carrier Proteins↗
PubMed1982

Effect of phospholipid oxidation products on transbilayer movement of phospholipids in single lamellar vesicles.

Single lamellar phosphatidyl[methyl-2H]choline vesicles were incubated with an excess of unlabeled phosphatidylcholine vesicles or phosphatidylcholine-cholesterol vesicles containing 8 mol % glucuronosyldiglyceride. Incubation of the two vesicle populations was performed in the presence or absence of a purified phosphatidylcholine exchange protein. The negatively charged glycolipid donor vesicles could be completely removed by column chromatography on DEAE-Sephacel. Following incubation with exchange protein and subsequent fractionation, the -N(CD3)3 phosphatidylcholine acceptor vesicles exhibited a 61-73% enrichment of the unlabeled phosphatidylcholine in the outer monolayer. Upon incubation in an air atmosphere, no appreciable transbilayer movement of the outer monolayer -N(CH3)3 phosphatidylcholine was observed for at least 5 days. Between days 5 and 7, however, extensive transbilayer movement occurred, leading to an outer monolayer/inner monolayer phosphatidylcholine ratio of 2.1 on day 7. In phosphatidylcholine-6 mol % cholesterol vesicles treated similarly, the outside/inside ratio of the unlabeled phospholipid was 6.7, suggesting a much smaller percentage of transbilayer movement. The loss of transbilayer asymmetry which occurred during a 36-h period after day 5 could be estimated at the upper limit, t 1/2 approximately 7.3 h for phosphatidylcholine vesicles and t 1/2 approximately 53 h for phosphatidylcholine-cholesterol vesicles. The actual rates for transbilayer movement, however, were likely more rapid. Transbilayer movement occurred at a time period when oxidized phospholipid breakdown products had reached critical levels.

Androgen-Binding Protein↗
PubMed2000

Phospholipid-bound beta 2-glycoprotein I induces the production of anti-phospholipid antibodies.

Apoptotic-cell-bound beta2-glycoprotein I (beta2GPI), but not apoptotic cells or beta2GPI alone, can induce the production of anti-phospholipid (anti-PL) antibodies (Ab) in normal mice. Although it is presumed that beta2GPI binds to anionic phospholipid (PL) exposed on the apoptotic cell membrane, the precise nature of this complex and its immunogenicity is unclear. To address these issues, we investigated the structure and immunogenicity of human beta2GPI in the presence of different PL that may be expressed on the surface of apoptotic cells. BALB/c mice were immunized intravenously (iv) with beta2GPI in the presence of cardiolipin (CL), phosphatidylglycerol (PG), phosphatidylserine (PS), phosphatidylcholine (PC), or PS/PC (25%/75%) vesicles. Cardiolipin+beta2GPI induced the highest levels of anti-beta2GPI and anti-CL IgG Ab and lupus anticoagulant (LA) activity, while beta2GPI with PC or PS/PC vesicles produced no significant anti-PL Ab. PS+beta2GPI was somewhat immunogenic, but less so than PG+beta2GPI. beta2GPI was immunogenic in the presence of native (CL(N)), but not hydrogenated (CL(H)), CL. Circular dichroism analysis demonstrated that the structure of beta2GPI was altered specifically by interaction with CL(N), but not other anionic PL, including CL(H). Similarly, the structure of CL(N)was affected by interaction with beta2GPI, as detected by(31)P nuclear magnetic resonance. These findings demonstrate that beta2GPI complexed with CL(N)is structurally altered, highly immunogenic, and induces the production of IgG anti-PL Ab. Furthermore, the structural modification and the generation of immunogenic epitopes on beta2GPI upon interaction with CL(N)require the presence of unsaturated fatty acid chains, suggesting a role for oxidation in this process.

Adjuvants, Immunologic↗
PubMed1992

Regulation of the skeletal sarcoplasmic reticulum Ca(2+)-ATPase by phospholamban and negatively charged phospholipids in reconstituted phospholipid vesicles.

The Ca(2+)-ATPase of skeletal sarcoplasmic reticulum was purified and reconstituted in proteoliposomes containing phosphatidylcholine (PC). When reconstitution occurred in the presence of PC and the acidic phospholipids, phosphatidylserine (PS) or phosphatidylinositol phosphate (PIP), the Ca(2+)-uptake and Ca(2+)-ATPase activities were significantly increased (2-3 fold). The highest activation was obtained at a 50:50 molar ratio of PS:PC and at a 10:90 molar ratio of PIP:PC. The skeletal SR Ca(2+)-ATPase, reconstituted into either PC or PC:PS proteoliposomes, was also found to be regulated by exogenous phospholamban (PLB), which is a regulatory protein specific for cardiac, slow-twitch skeletal, and smooth muscles. Inclusion of PLB into the proteoliposomes was associated with significant inhibition of the initial rates of Ca(2+)-uptake, while phosphorylation of PLB by the catalytic subunit of cAMP-dependent protein kinase reversed the inhibitory effects. The effects of PLB on the reconstituted Ca(2+)-ATPase were similar in either PC or PC:PS proteoliposomes, indicating that inclusion of negatively charged phospholipid may not affect the interaction of PLB with the skeletal SR Ca(2+)-ATPase. Regulation of the Ca(2+)-ATPase appeared to involve binding with the hydrophilic portion of phospholamban, as evidenced by crosslinking experiments, using a synthetic peptide which corresponded to amino acids 1-25 of phospholamban. These findings suggest that the fast-twitch isoform of the SR Ca(2+)-ATPase may be also regulated by phospholamban although this regulator is not expressed in fast-twitch skeletal muscles.

Affinity Labels↗
PubMed1979

Phospholipid metabolism in Neisseria gonorrhoeae: phospholipid hydrolysis in nongrowing cells.

Hydrolysis of cell envelope phospholipids was demonstrated in cells of both autolytic and nonautolytic strains of Neisseria gonorrhoeae that were labeled during growth in the presence of [3H] acetate. The label incorporated into the cellular phospholipids was located exclusively in the fatty acid acyl side chains. Labeled cells were incubated for 2 hr in N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid buffer, pH 8.5, containing various additions, and then examined for distribution of 3H in lipids. Ca++ selectively stimulated the deacylation of phosphatidylethanolamine (PE), whereas Mn++ stimulated the deacylation of phosphatidylglycerol (PG). Hydrolysis of phosphatidylethanolamine by phospholipase A was accompanied by the accumulation of lysophosphatidylethanolamine (LPE) and free fatty acids in the cells. Free fatty acids accumulated to a greater extent than lysophosphatidylethanolamine, suggesting that the latter was further hydrolyzed to glycerophosphorylethanolamine (GPE) and free fatty acids by a lysophospholipase. Methanol, ethanol, propanol, and isopropanol, added at concentrations which inhibited growth by 50%, stimulated phospholipase A, but not lysophospholipase activity. Differences in heat inactivation, metal ion requirements, and pH optima suggested that phospholipase A activities with phosphatidylethanolamine or phosphatidylglycerol as substrate and lysophospholipase may be separate enzymes.

Buffers↗
PubMed1986

Phospholipid base exchange in human leukocyte membranes: quantitation and correlation with other phospholipid biosynthetic pathways.

The biosynthesis of phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylserine (PS) by base-exchange reactions, and of PC and PE by the CDP pathways, was assessed in the membrane phospholipids of human leukocytes (neutrophils, lymphocytes, T lymphocytes, non-T lymphocytes, and monocytes). Of the three base-exchange activities, ethanolamine exchange was the highest and choline exchange the lowest in each leukocyte membrane. In the CDP pathways, ethanolaminephosphotransferase (EPT) and cholinephosphotransferase (CPT) had comparable activities. Among subpopulations of leukocytes, T lymphocytes showed the highest levels of each enzyme activity, and neutrophils showed the least. In contrast to the enzymes of the CDP pathways, each base-exchange activity was directly proportional to the Ca2+ concentration, but markedly inhibited by Mg2+. Despite this Ca2+ dependence, the base-exchange activities were increased in a dose-dependent manner by calmodulin antagonists and, except for ethanolamine exchange, inhibited by the addition of calmodulin; EPT and CPT activities were only slightly inhibited by calmodulin antagonists and were unaffected by calmodulin. PE formation in both neutrophil and lymphocyte base-exchange reactions was enhanced in a dose-dependent manner by the presence of low concentrations of bioactive stimulants (zymosan, 0.05-0.2 mg/ml; Con A, 0.5-2 micrograms/ml), while EPT and CPT activities were not increased by these cell stimulants. Taken together, our data suggest that base-exchange activity, the biological significance of which has been hitherto unclear, may be related to cell activation; in contrast, the CDP pathways appear primarily to involve the constitutive biosynthesis of phospholipids. Our data further suggest that ethanolamine required for base-exchange reactions is a precursor of PE, N-transmethylation of which can serve as a source of cell activation, leading to production of arachidonic through PC by mediation of phospholipase A2 activity.

Calcium↗
PubMed1978

Phospholipid substitution of the purple membrane. The stoichiometry of light-induced proton release by phospholipid-substituted purple membranes.

The method of Warren et al. (1974, Proc. Natl. Acad. Sci. U.S. 71, 622--626) was employed to substitute the polar lipids of the purple membrane of Halobacterium halobium by different phosphatidylcholine species. Substitution at pH 6.5 yields proteolipid complexes in the form of bent open sheets which have a protein to lipid phosphorus ratio similar to the natural membrane, i.e. about 1 : 10 (mol/mol). The extent of substitution increases with the length of the fatty acid chain of the phosphatidylcholine used. The spectral properties of bacteriorhodopsin are only slightly affected by substitution of 95% of the lipid, except that the photocycle is slowed down appreciably. Due to this slow rate the M412 intermediate of the cycle accumulates in the light. Associated with this accumulation is a net light-induced proton release, which proved insensitive to uncoupler. A comparison between the net proton release and the amount of M412 accumulated, studied as a function of pH, shows that no fixed stoichiometry exists between the two processes. Phospholipid substitution by egg phosphatidylcholine at pH 7.5 or by egg phosphatidylethanolamine leads to preparations of purple membrane with 15 or 25 mol of phospholipid per mol of bacteriorhodopsin, respectively. These preparations seem to consist of closed membrane structures. They take up protons in the light in an uncoupler-sensitive way.

Bacteriorhodopsins↗
PubMed1980

The influence of poly(L-lysine) on phospholipid polymorphism. Evidence that electrostatic polypeptide-phospholipid interactions can modulate bilayer/non-bilayer transitions.

31P-NMR shows that poly(L-lysine) binding to cardiolipin, phosphatidylserine or phosphatidylglycerol does not affect the macroscopic structure or local order (in the phosphate region) of the phospholipids. In the case of cardiolipin poly(L-lysine) inhibits the ability of Ca2+ to induce the hexagonal HII phase. Alternatively, poly(L-lysine) induces the hexagonal HII phase for a fraction of the phospholipids in phosphatidylethanolamine-cardiolipin (2:1) dispersions.

Calcium↗
PubMed1986

Bacterial cytotoxins, amphotericin B and local anesthetics enhance transbilayer mobility of phospholipids in erythrocyte membranes. Consequences for phospholipid asymmetry.

Incorporation of the channel-forming polyene antibiotic amphotericin B and of cytotoxins from Staphylococcus aureus (alpha-toxin) or Pseudomonas aeruginosa into erythrocyte membranes results in a concentration-dependent enhancement of the flip rates of exogenous lysophosphatidylcholine. The flip rate is also enhanced by incorporation of tetracaine and dibucaine. Removal of tetracaine and amphotericin B from the cells normalizes the flip rates. In parallel to the enhancement of flip rates, alpha-toxin produces a loss of transmembrane asymmetry of both phosphatidylethanolamine and phosphatidylserine. Pretreatment of cells with amphotericin or high concentrations (over 2.5 mmol . l-1) of tetracaine, followed by removal of the perturbing agent by washing, produces a selective loss of the asymmetric orientation of phosphatidylethanolamine to the inner membrane layer, as evaluated by the accessibility of the lipid towards cleavage by phospholipase A2. The extent to which asymmetry is lost depends on the time of pretreatment with amphotericin or tetracaine, indicating a limitation by the rate of reorientation of phosphatidylethanolamine to the outer membrane surface. Evaluation of the accessibility of phosphatidylethanolamine towards cleavage by phospholipase A2 in the presence of local anesthetics indicates accessible fractions much higher than those obtained after removal of the perturbant. In the presence of tetracaine, endofacial phosphatidylethanolamine seems somehow to become accessible to phospholipase A2. Phosphatidylserine does not exhibit this peculiarity. The results indicate that various types of perturbation of the lipid domain of the erythrocyte membrane may enhance the transbilayer mobility of phospholipids as well as destabilize the asymmetric distribution of aminophospholipids. However, as in other instances reported previously (Haest, C.W.M., Erusalimsky, J., Dressler, V., Kunze, I. and Deuticke B. (1983) Biomed. Biochim. Acta 42, 17-21), there is no tight coupling between transbilayer mobility and destabilization of asymmetry of the transbilayer distribution of phospholipids.

Amphotericin B↗
PubMed1990

The conformational changes of apocytochrome c upon binding to phospholipid vesicles and micelles of phospholipid based detergents: a circular dichroism study.

The influence of lipid aggregates on the secondary structure of the mitochondrial precursor protein apocytochrome c was investigated by circular dichroism techniques. A conformational change of the protein from a random coil to partially alpha-helical structures was observed upon binding to negatively charged DOPS SUVs. Also DOPC SUVs showed to induce such a conformational change, but to a lesser extent. The detergents decyl-, lauryl and myristoyl-phosphoglycol or -phosphocholine, were synthesized as micel forming phospholipid analogs and are shown to mimic the phospholipids well in their ability to induce alpha-helices in the protein. A full assignment of the regions where the possible alpha-helices are formed is proposed by making use of derived fragments of apocytochrome c, prediction methods and the known X-ray structure of cytochrome c. Besides a helix at the N-terminus (residues 1-22) and at the C-terminal part (residues 80-101), two regions in the middle section (residues 49-54 and 59-70) are suggested to be helical. It is inferred that the two cysteines in the positions 14 an 17 at the N-terminal part are facing in the same direction, which could facilitate the covalent attachment of the heme group to the precursor in the translocation process.

Animals↗
PubMed1992

Effect of pulmonary surfactant protein B (SP-B) and calcium on phospholipid adsorption and squeeze-out of phosphatidylglycerol from binary phospholipid monolayers containing dipalmitoylphosphatidylcholine.

The pulsating bubble technique was used to study the surface activity of binary phospholipid mixtures containing dipalmitoyl-phosphatidylcholine (DPPC) and an unsaturated acidic phospholipid such as egg phosphatidylglycerol (egg PG), 1-palmitoyl-2-oleoyl-PG (POPG) or egg phosphatidic acid (egg PA) in the presence of surfactant-associated protein B (SP-B) and calcium. The relative surface activities were DPPC/egg PG/SP-B (7:3:1%) greater than DPPC/POPG/SP-B (7:3:1%) greater than DPPC/egg PA/SP-B (7:3:1%). The Wilhelmy surface plate technique was utilized to investigate the interaction between pure SP-B in the bulk phase (0.9% NaCl/1.5 mM CaCl2) and preformed DPPC or phosphatidylglycerol (PG) monolayers. Although SP-B injected into the bulk phase reduces the surface tension of a clean surface, no evidence was obtained for the insertion of SP-B into surface monolayers at equilibrium surface tension. Surface radioactivity measurements and the Wilhelmy surface plate technique were also used to study the potential interactions between liposomes of DPPC/POPG (7:3) with or without SP-B and surface monolayers of [14C]DPPC or [14C]POPG. No exchange of phosphatidylcholine (PC) or PG was found between the monolayer and liposomes. We also compared the adsorption of pure POPG or 1-palmitoyl-2-oleoyl- phosphatidylcholine (POPC) and binary mixed liposomes with DPPC in the presence or absence of SP-B and calcium. DPPC/POPG/SP-B (7:3:1%) was found to be more surface active than pure POPG plus 1% SP-B in the presence of calcium. Injection of SP-B into the bulk phase promoted the adsorption of DPPC/POPG liposomes to a greater extent than POPG liposomes. The enhanced adsorption was dependent on the presence of calcium. In contrast to PG, DPPC/POPC/SP-B (7:3:1%) was less surface active than pure POPC plus 1% SP-B either in the presence or absence of calcium. Our findings suggested that the molecular composition and organization of mixed monolayers play an important role in the surface activity of the surfactant.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1985

Phospholipid and ether linked phospholipid content alter with cellular resistance to vinblastine.

The phospholipid and ether linked phospholipid content of leukaemic lymphocytes alters when the cells become resistant to low levels of the anti-cancer drug, vinblastine. Sphingomyelin and cardiolipin increase, and phosphatidyl ethanolamine and serine decrease in resistant cells. In addition, increases in 1-alkyl-2-acyl phosphatidyl choline and 1-alkenyl-2-acyl-phosphatidyl ethanolamine are concomitant with decreased 1,2-diacyl phosphatidyl choline and ethanolamine. Changes to the ultrastructure of the inner half of the plasma membrane bilayer, as a consequence of drug resistance, are illustrated by freeze-fracture electron microscopy.

Binding Sites↗