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PubMed1996

Evidence for the formation of amphotericin B-phospholipid complexes in Langmuir monolayers.

PURPOSE: To study the interaction of the polyene antifungal amphotericin B with phospholipid Langmuir monolayers and to correlate with stability of phospholipid-stabilized drug emulsions. METHODS: Pressure-area isotherms of mixed monolayers of amphotericin B (0-20 mol%) and different phospholipid types were recorded using conventional Langmuir trough methods. Emulsion stability of amphotericin B-containing lipid emulsions was measured using dynamic light scattering. RESULTS: Incorporation of amphotericin B into monolayers composed of saturated phospholipids (Lipoid E80-3) had a profound effect on the shape of the isotherm. This effect was directly related to the concentration of amphotericin B in the monolayer. At high drug concentrations, the shape of the isotherms became progressively similar to that of pure DPPC, thus exhibiting regions attributable to phospholipid in different phase states. This effect on isotherm shape was not observed following incorporation of the drug into monolayers composed of the equivalent unsaturated lecithin (Lipoid E80). CONCLUSIONS: These results are interpreted as indicating the formation of an amphotericin B-phospholipid complex, resulting in phase separation within the monolayer. The extent and nature of this phase separation was dependent on both the concentration of drug in the system, and the saturation state of the phospholipid component. The relevance of these observations to the stability of amphotericin B drug emulsions stabilised by saturated and unsaturated phospholipid emulsifiers is discussed. These observations may also be relevant to the toxicity of these, and other novel amphotericin B formulations.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1982

The phospholipids of the hepatic endoplasmic reticulum. Structural change in liver injury.

Endoplasmic-reticulum phospholipids were measured during the first hour after carbon tetrachloride administration to male Sprague-Dawley rats and compared with carbon tetrachloride challenge of microsomes from control animals in vitro. The extracted lipids were separated by high-pressure liquid chromatography. No significant differences in the abundance of phosphatidylserine, phosphatidylethanolamine, phosphatidylinositol or phosphatidylcholine were found after either treatment when compared with untreated controls. Diene conjugate formation in each separated phospholipid was determined by measuring A(232) and expressed on the basis of lipid phosphorus. Phosphatidylserine was peroxidized 6-fold greater than in controls after challenge in vivo, reaching maximal change after 15min, whereas the other phospholipids showed little or no alteration. Fatty acid composition analysis was performed by g.l.c. after transesterification of individual phospholipids. Phosphatidylserine revealed two types of response: an abrupt decrease in relative abundance of oleic acid (C(18:1)) and linoleic acid (C(18:2)) without further loss and a slower, linear decrease in arachidonic acid (C(20:4)) over the first hour. Similar changes were not seen in other phospholipids. In the ;in vitro' model, the relative amounts of the phospholipids do not change. The extent of peroxidation was greater in all the phospholipids than found in vivo, with phosphatidylserine peroxidized to the greatest extent. These data suggest that carbon tetrachloride injury in vivo produces an early peroxidative event and that a specific phospholipid (phosphatidylserine) is selectively modified, although maintaining its relative concentration in the membrane. Dissection of this process in vitro will require refinement of existing systems to reduce the non-specific changes associated with the model system.

Adenosine Diphosphate↗
PubMed1981

Bridging of IgE receptors activates phospholipid methylation and adenylate cyclase in mast cell plasma membranes.

Bridging of IgE receptors on normal rat mast cells by divalent anti-receptor antibodies induced phospholipid methylation and an increase in intracellular cyclic AMP within 15 sec after the receptor bridging. These biochemical events were followed by Ca2+ influx and histamine release. When IgE receptors on isolated plasma membranes were bridged by the antibody, both the increase in the incorporation of [3H]methyl into lipid fraction and the synthesis of cyclic AMP were demonstrated. The synthesis of cyclic AMP in this system was enhanced in the presence of GTP. The results indicated that the bridged IgE receptors are linked to both methyltransferases and adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] in the plasma membrane. An increase in cyclic AMP prior to receptor bridging suppressed phospholipid methylation in the plasma membrane, Ca2+ uptake, and subsequent histamine release. On the other hand, inhibition of phospholipid methylation by (S)-isobutyryl-3-deazaadenosine resulted in the suppression of cyclic AMP synthesis in the plasma membrane. These findings suggest that the activation of phospholipid methylation and the activation of adenylate cyclase are e, and subsequent histamine release. On the other hand, inhibition of phospholipid methylation by (S)-isobutyryl-3-deazadenosine resulted in the suppression of cyclic AMP synthesis in the plasma membrane. These findings suggest that the activation of phospholipid methylation and the activation of adenylate cyclase are e, and subsequent histamine release. On the other hand, inhibition of phospholipid methylation by (S)-isobutyryl-3-deazadenosine resulted in the suppression of cyclic AMP synthesis in the plasma membrane. These findings suggest that the activation of phospholipid methylation and the activation of adenylate cyclase are mutually regulated.

Adenylyl Cyclases↗
PubMed1987

Metabolism of extracellular phospholipids in Tetrahymena pyriformis.

We studied the metabolism of phospholipids exogenously added to cultures of the protozoan, Tetrahymena pyriformis. Tetrahymena cells were found to metabolize the extracellular phospholipids and the fatty acyl chains of the latter were accumulated predominantly as a form of triacylglycerol in the cells. This metabolism was considered to be initiated via endocytosis of phospholipid vesicles, as judged from the following facts: Cytochalasin B, an inhibitor of endocytosis, suppressed the metabolism almost completely. Phospholipid vesicles were incorporated into a phagosome-like structure in Tetrahymena cells, as observed under an electron microscope. When phospholipids doubly labeled with 14C and 3H at the glycerol moiety and fatty acyl chain, respectively, were incubated with Tetrahymena cells, the glycerol moiety and fatty acyl chain at the sn-2-position of the exogenous phospholipids were incorporated into the cellular triacylglycerol fraction in a 1 to 1 ratio. Monoacylglycerol acyltransferase activity was detected in the microsomal fraction of Tetrahymena cells. From these results, together with those of our previous study on lysosomal phospholipid hydrolysis in Tetrahymena (J. Biochem. 99, 125-133 (1986)), it is suggested that the extracellular phospholipids which were taken up by the cells via endocytosis were hydrolyzed through the action of lysosomal phospholipases A1 and C, and also that one of the products, sn-2-monoacylglycerol, served as an acyl acceptor for the synthesis of triacylglycerol via the microsomal "monoacylglycerol pathway."

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1980

Involvement of phospholipids in polyunsaturated Fatty Acid synthesis in developing soybean cotyledons.

Developing soybean (cv. Dare) cotyledons harvested at 30 days after flowering were pulse-labeled with [1-(14)C]oleoyl-CoA. The metabolic interrelation of radiolabeled unsaturated fatty acids between the major glycerolipid classes was determined at various time intervals. At chase time zero, [(14)C]oleic acid accounted for 99.2% of the total glycerolipid radioactivity, and phospholipids contained 92% of the total incorporated radioactivity. With time, phospholipids were metabolized in triacylglycerol biosynthesis and radioactivity was detected in polyunsaturated fatty acids. The hypothesis that phospholipids were metabolic intermediates in polyunsaturated fatty acid biosynthesis was tested by comparing the theoretical and the actual amount of radiolabeled oleic acid that was associated with triacylglycerol as a function of time. The radioactive oleic acid found in triacylglycerol at various intervals was derived from phospholipids via a diacylglycerol intermediate. Assuming no phospholipid desaturation, the potential or theoretical amounts of [(14)C]oleic acid that could be transferred to triacylglycerol from phospholipids was defined by a system of differential equations. The results demonstrated that the decline in [(14)C]oleic acid from phospholipid after long chase intervals was equal to the total amount of radioactive unsaturated fatty acids found in neutral lipids. The difference between the theoretical and actual amounts of [(14)C]oleic acid present in triacylglycerol after long time intervals was equal to the amount of radioactivity present in polyunsaturated fatty acids. Based upon those findings in soybeans, the desaturation of oleic acid associated with phospholipids was highly probable.

Journal Article↗
PubMed1982

Regulation by Lipids of Plant Microsomal Enzymes: III. Phospholipid Dependence of the Cytidine-Diphospho-Choline Phosphotransferase of Potato Microsomes.

Cytidine-diphospho-choline diacyl-glycerol phosphorylcholine phosphotransferase activity was demonstrated in potato (Solanum tuberosum L.) microsomes and the incorporation of cytidine-diphospho[(14)C]choline into phosphatidylcholine was characterized by the time course of (14)C incorporation and the effect of microsomal protein concentration on choline incorporation.Potato microsomes were progressively delipidated by treatments (2 min at 0 degrees C) with increasing amounts of phospholipase C from Bacillus cereus. A decrease in choline phosphotransferase activity was observed in parallel with the progressive hydrolysis of membrane phospholipids. A 70% (or more) phospholipid hydrolysis provoked the total inactivation of the enzyme.Adding back exogenous phospholipids (in the form of liposomes) to phospholipase C-treated membranes restored the enzymic activity. Restoration could be obtained with egg yolk phospholipids as well as with potato phospholipids. Restoration was time dependent and completed after 10 minutes; restoration was also dependent on the quantity of liposomes added to lipid-depleted membranes: the best restorations were obtained with 1 to 2.5 milligrams of phospholipid per mg of microsomal protein; higher phospholipid to protein ratios were less efficient or inhibitory.These results clearly demonstrate the phospholipid dependence of the cytidine-diphospho-choline phosphotransferase from potato microsomes.

Journal Article↗
PubMed1982

Changes in microsomal membrane microviscosity and phospholipid methyltransferases during rat liver regeneration.

During regeneration of rat liver newly synthesized molecules of drug-metabolizing enzymes, like cytochrome P450, are incorporated into proliferating endoplasmic reticulum (ER). Decreased membrane microviscosity facilitates incorporation of the enzyme-protein molecules into the phospholipid matrix of ER. The microviscosity of membranes is altered by: (1) changed ratios of phospholipid to cholesterol, (2) unsaturation of fatty acids in phospholipids, and (3) methylation of phospholipids. Alterations are known to occur in (1) and (2) in the plasma membrane of proliferating cells. Microviscosity and phospholipid methyltransferases in ER have not been investigated during liver regeneration. Therefore, microviscosity and S-adenosyl-L-methionine (SAM) mediated methylation of phosphatidylethanolamine to phosphatidyl-N-methylethanolamine (PME) and phosphatidylcholine (PC) were measured using microsomal membranes of regenerating rat livers at 6-96 h after partial hepatectomy. In the methylated phospholipids, the proportion of PME increased by 3-9% at 1 microM SAM, and, at 200 microM SAM, the proportion of PC decreased by about 5-10% at 12-24 h. Two phase transitions were observed with microsomal membranes between 20 and 40 degrees C. In synthetic liposomes containing PE, PME and PC, microviscosity decreased when the proportion of PME increased or the proportion of PC decreased. Therefore, alterations in phospholipid methyltransferases and consequent changes in membrane phospholipid methylation may contribute to increased membrane fluidity during cell proliferation and incorporation of drug-metabolizing enzymes into ER.

Animals↗
PubMedDate not supplied

Standardization of immunoassays for antiphospholipid antibodies with beta 2GPI and role of other phospholipid cofactors.

Presence of beta 2 Glycoprotein I (beta 2GPI), in addition to phospholipids, is an absolute requirement for binding APA. This binding is frequently observed with beta 2GPI coated alone, however many APA react only with beta 2GPI complexed to phospholipids, but not with phospholipids alone. We demonstrate that a subgroup of rabbit polyclonal antibodies to human beta 2GPI binds to this protein only when it is coated on a solid surface, but not if it is in solution. In addition, beta 2GPI present in goat serum is strongly fixed by the coated phospholipids and the complexes formed bind as well APA as the rabbit antibodies to beta 2GPI. The diluent used for testing APA, has a strong incidence on APA's reactivity as it can be a source of beta 2GPI. Antibody binding to beta 2GPI, Prothrombin, Protein S, and Annexin V, coated in the presence or in the absence of phospholipids, was tested in 55 patients with the antiphospholipid syndrome. The strongest binding of antibodies was observed in 39 plasma to a mixture of phospholipids and purified human beta 2GPI, however 17 samples also presented a significant reactivity to beta 2GPI alone. Nine plasmas contained antibodies to Prothrombin, 4 to Protein S, 3 to Annexin V, and 1 to Protein C. We conclude that most of the APA are directed to a complex of beta 2GPI and phospholipids although in some patients antibodies to beta 2GPI alone or to other phospholipid binding proteins are present.

Animals↗
PubMed2003

Sulfatides: targets for anti-phospholipid antibodies.

BACKGROUND: Sulfatides are sulfated glycosphingolipids expressed on the surface of erythrocytes, leukocytes, and platelets. Sulfatides interact with several cell adhesion molecules involved in hemostasis. Beta2-glycoprotein I is an anionic phospholipid-binding plasma protein, and the phospholipid-bound form is the target for most anti-phospholipid antibodies that are associated with recurrent thrombosis, miscarriages, and neurological symptoms. In this study, we examined whether beta2-glycoprotein I forms a complex with sulfatides and thereby becomes a target for anti-phospholipid antibodies. METHODS AND RESULTS: Beta2-glycoprotein I binds to surface-bound sulfatides but not to other glycolipids, such as ceramide, cerebrosides, sphingomyelin, or ganglioside. At a sulfatide coating density of 1 microg/well, beta2-glycoprotein I reaches half-maximal binding at 2.5 microg/mL, and the binding is saturated at 10 microg/mL. The binding of beta2-glycoprotein I also depends on the coating density of sulfatides in the well. At a constant beta2-glycoprotein I concentration of 5 microg/mL, maximal binding of beta2-glycoprotein I is observed at a coating density of 1 mug/well. The serum from 14 patients with anti-cardiolipin antibodies, a subset of anti-phospholipid antibodies, bound to sulfatide-bound beta2-glycoprotein I and previous absorption on cardiolipin-coated surfaces decreased the immunoreactivity toward sulfatide-beta2-glycoprotein I complex by >50% in 12 of 14 patients. Furthermore, immunoaffinity-purified anti-cardiolipin antibodies from 4 of 5 patients reacted with sulfatide-bound beta2-glycoprotein I. CONCLUSIONS: These results show that not only anionic phospholipids, as commonly known, but also sulfatides are targets for most anti-phospholipid antibodies. We therefore postulate that interactions of these antibodies with sulfatides may contribute to some of the clinical symptoms of the anti-phospholipid antibody syndrome.

Antibodies, Anticardiolipin↗
PubMedDate not supplied

Role of topical phospholipids in the prophylaxis of silicone elastomer-associated infection in the abdominal cavity.

The present study evaluated the influence of phospholipids (phosphatidyl choline and phosphatidyl inositol) on the prevention of abdominal biomaterial-associated infection. Phospholipid-impregnated silicone elastomer (SE) fragments were either intraperitoneally implanted in rats or immersed in serum for 0, 4, and 14 days, and 3 x 10(9) cfu of 3H-labeled, live Escherichia coli were added in the peritoneal cavity or in vitro incubation medium. Three hours after incubation, the adherence of bacteria significantly decreased to phospholipid-impregnated SE fragments, which had been immersed/implanted for 0 and 4 days. However, the number of adhering bacteria did not differ between the impregnated and unimpregnated SE fragments after 14 days of immersion/implantation. A significantly lower number of adhering bacteria was noted on all unimpregnated SE fragments when phospholipid was supplemented in the peritoneal cavity or in vivo medium, compared with fragments with no supplement. The rate of bacterial DNA synthesis decreased significantly after incubation with phospholipid 2 h or more. Phospholipids did not further influence peritoneal morphology. Thus topical administration of phospholipids by impregnation to the surface of SE fragments or supplement in the incubation medium prevented bacterial adherence onto the SE fragments. This implies that the use of phospholipids might be a mode of preventing biomaterial-associated infections.

Administration, Topical↗
PubMed2002

Increased exposure of anionic phospholipids on the surface of tumor blood vessels.

Anionic phospholipids are largely absent from the external leaflet of the plasma membrane of mammalian cells under normal conditions. Exposure of phosphatidylserine on the cell surface occurs during apoptosis, necrosis, cell injury, cell activation, and malignant transformation. In the present study, we determined whether anionic phospholipids become exposed on tumor vasculature. A monoclonal antibody, 9D2, which specifically recognizes anionic phospholipids, was injected into mice bearing a variety of orthotopic or ectopic tumors. Other mice received annexin V, a natural ligand that binds to anionic phospholipids. Both 9D2 and annexin V specifically localized to vascular endothelium in all of the tumors, and also to tumor cells in and around regions of necrosis. Between 15 and 40% of endothelial cells in tumor vessels were stained. No localization was detected on normal endothelium. Various factors and tumor-associated conditions known to be present in the tumor microenvironment were examined for their ability to cause exposure of anionic phospholipids in cultured endothelial cells, as judged by 9D2 and annexin V binding. Hypoxia/reoxygenation, acidity, thrombin, and inflammatory cytokines all induced exposure of anionic phospholipids. Hydrogen peroxide was also a strong inducer. Combined treatment with inflammatory cytokines and hypoxia/reoxygenation had greater than additive effects. Possibly, injury and activation of tumor endothelium by cytokines and reactive oxygen species induce exposure of anionic phospholipids, most likely phosphatidylserine. Anionic phospholipids on tumor vessels could potentially provide markers for tumor vessel targeting and imaging.

Animals↗
PubMed1986

Comparison of the effects of muscarine and vasopressin on inositol phospholipid metabolism in the superior cervical ganglion of the rat.

Both muscarine and vasopressin have been shown previously to increase the accumulation [3H]inositol phosphates in superior cervical ganglia in which the phospholipids were labeled with [3H] inositol. In this study, we have compared the effects of muscarine and of vasopressin on phospholipid metabolism in the ganglion. The effects of these agents on [3H]inositol phosphate accumulation are additive. The response to muscarine levels off after approximately 10 min, whereas the response to vasopressin increases for at least 30 min. The incorporation of [3H]inositol into phospholipids is enhanced in decentralized ganglia and in ganglia maintained in organ culture compared to freshly isolated ganglia. These treatments appear to potentiate the effect of muscarine on [3H]inositol phosphate accumulation, but do not affect the response of the ganglia to vasopressin. Muscarine and vasopressin also increase the incorporation of [3H]inositol into phospholipids in the ganglion. Autoradiographic techniques were used to localize the inositol-containing phospholipids in the ganglion. Muscarine increases phospholipid labeling primarily in the cell bodies of the principal ganglionic neurons, whereas vasopressin increases phospholipid labeling primarily in the neuropil. These data are consistent with the hypothesis that muscarine and vasopressin stimulate the hydrolysis of different pools of ganglionic phospholipids.

Animals↗
PubMed1987

[Nonenzymatic incorporation of prostaglandin A1 into phospholipids in rat liver microsomes].

The incorporation of [5,6(n)-3H]prostaglandin A1 (PGA1) and [1-14C]oleic acid into membrane phospholipids of rat liver microsomes was studied. It was shown that PGA1 is incorporated into phospholipids in a much lesser degree than oleic acid. PGA1 is incorporated into phosphatidylethanolamine and, in a lesser degree, into phosphatidylcholine and phosphatidylinositol + phosphatidylserine. The exogenous cofactors of fatty acid acylation (ATP, CoA, Mg2+) exert no marked influence on the incorporation of PGA1 into the phospholipids. PGA1 interacts with isolated rat liver phospholipids; the PGA1-phospholipid conjugate formed is not destroyed in the course of one- or two-dimensional thin-layer chromatography. On the other hand, PGA1 binding to unsaturated phosphatidylcholines is strictly dependent on the phospholipid oxidation index. It is concluded that PGA1 incorporation into rat liver phospholipids is a result of interaction of PGA1 with peroxidized phospholipids.

Animals↗
PubMed1986

Specific pools of phospholipids are used for lipoprotein secretion by cultured rat hepatocytes.

Since phospholipids are major components of all serum lipoproteins, the role of phospholipid biosynthesis in lipoprotein secretion from cultured rat hepatocytes has been investigated. In liver, phosphatidylcholine is made both by the CDP-choline pathway and by the methylation of phosphatidylethanolamine, which in turn is derived from both serine (via phosphatidylserine) and ethanolamine (via CDP-ethanolamine). Monolayer cultures of rat hepatocytes were incubated in the presence of [methyl-3H]choline, [1-3H] ethanolamine, or [3-3H]serine. The specific radioactivity of the phospholipids derived from each of these precursors was measured in the cells and in the secreted lipoproteins of the cultured medium. The specific radioactivities of phosphatidylcholine and phosphatidylethanolamine derived from [1-3H]ethanolamine were markedly lower (approximately one-half and less than one-tenth, respectively) in the secreted phospholipids than in the cellular phospholipids. Thus, ethanolamine was not an effective precursor of the phospholipids in lipoproteins. On the contrary, the specific radioactivity of phosphatidylcholine made from [methyl-3H]choline was approximately equal in cells and lipoproteins. In addition, over the first 4 h of incubation with [3-3H]serine, the specific radioactivities of phosphatidylcholine and phosphatidylethanolamine were significantly higher in the lipoproteins than in the cells. These data indicate that there is not a random and homogeneous labeling of the phospholipid pools from the radioactive precursors. Instead, specific pools of phospholipids are selected, on the basis of their routes of biosynthesis, for secretion into lipoproteins.

Animals↗
PubMed1983

Incorporation of bovine enterokinase in reconstituted soybean phospholipid vesicles.

Bovine enterokinase was incorporated into vesicles reconstituted from a soybean phospholipid mixture. A thin film hydration procedure (MacDonald, R. I., and MacDonald, R. C. (1975) J. Biol. Chem. 250, 9206-9214) produced vesicles with 40% of the enterokinase activity bound in the membrane. The highest incorporation was observed when cholesterol or dimyristoylphosphatidylethanolamine was added to the soybean phospholipids. Crude and highly purified enterokinase preparations were incorporated to the same extent suggesting that other membrane components were not required for a successful reconstitution. The properties of enterokinase in phospholipid vesicles were compared with those of alkaline phosphatase, which was also added to the reconstitution system, and with the enzyme activities present in vesicles prepared from brush-border membranes. The enzyme activities were not released by solutions of high ionic strength and remained associated with the phospholipid vesicles on gel filtration, ultracentrifugation, and sucrose density centrifugation. Enterokinase and alkaline phosphatase had their active sites exposed to substrate in the brush-border membrane vesicles. In soybean phospholipid vesicles half of the active sites of both enzymes were on the outside, since release of the enzyme with Triton X-100 almost doubled the units of enzyme present. Incubation of the soybean phospholipid and brush-border membrane vesicles with papain released the exposed molecules of enterokinase. The released enzyme molecules were fully active but could not be reincorporated into phospholipid vesicles. This suggests that the structure imbedded in the lipid bilayer was essential for a successful reconstitution. We conclude that the reconstituted soybean phospholipid vesicles are a suitable membrane system for the further study of membrane-bound enterokinase.

Alkaline Phosphatase↗
PubMed2002

ABC transporters Cdr1p, Cdr2p and Cdr3p of a human pathogen Candida albicans are general phospholipid translocators.

We have used fluorescent 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD)-tagged phospholipid analogues, NBD-PE (phosphatidylethanolamine), NBD-PC (phosphatidylcholine) and NBD-PS (phosphatidylserine), to demonstrate that Cdr1p and its other homologues, Cdr2p and Cdr3p, belonging to the ATP-binding cassette (ABC) superfamily behave as general phospholipid translocators. Interestingly, CDR1 and CDR2, whose overexpression leads to azole resistance in C. albicans, elicit in-to-out transbilayer phospholipid movement, while CDR3, which is not involved in drug resistance, carries out-to-in translocation of phospholipids between the two monolayers of plasma membrane. Cdr1p, Cdr2p and Cdr3p could be further distinguished on the basis of their sensitivities to different inhibitors. For example, the in-to-out activity associated with Cdr1p and Cdr2p is energy-dependent and sensitive to sulphydryl blocking agents such as N-ethylmaleimide (NEM) and cytoskeleton disrupting agent cytochalasin E, while Cdr3p-associated out-to-in activity is energy-dependent but insensitive to NEM and cytochalasin E. We found that certain drugs, such as fluconazole, cycloheximide and miconazole, to which Cdr1p confers resistance could also affect in-to-out transbilayer movement of NBD-PE, while the same drugs had no effect on Cdr3p-mediated out-to-in translocation of NBD-PE. The ineffectiveness of these drugs to affect Cdr3p mediated out-to-in phospholipid translocation further confirms the inherent difference in the directionality of phospholipid translocation between these pumps. Notwithstanding the role of some of the Cdrps in drug resistance, this study clearly demonstrates that these ABC transporters of C. albicans are phospholipid translocators and this function could represent one of the physiological functions of such large family of proteins.

ATP-Binding Cassette Transporters↗
PubMed1983

Agglutination of mouse erythrocytes by binding of non-choline phospholipids to a 70 000-Dalton protein.

The structure of some phospholipids that cause agglutination of mouse erythrocytes has been studied. Haemagglutination is a property of non-choline-containing phospholipids; the phosphate group is essential and unsaturated fatty acids optimal. A protein of Mr 70 000 was isolated from mouse erythrocyte membranes which completely inhibited phospholipid-mediated erythrocyte agglutination. It is proposed that this protein is the phospholipid binding site on mouse erythrocytes and the ligand for the human B-lymphocyte receptor for mouse erythrocytes. Preliminary investigations suggest that a similar inhibitor of phospholipid-mediated agglutination is found in serum. Agglutination of mouse erythrocytes by phospholipid and specific inhibition by the 70 kDa membrane protein constitute a simple system for studying the interaction of phospholipid with protein.

Animals↗
PubMed1996

Acyl chain and headgroup specificity of human plasma phospholipid transfer protein.

Phospholipid transfer protein (PLTP) is a plasma protein with two reported in vitro activities: transfer of phospholipids and modulation of HDL particle size. The mechanism of PLTP-mediated phospholipid transfer was studied by determining the acyl chain and headgroup specificity and comparing the results with those obtained with the non-specific lipid transfer protein (ns-LTP), a previously characterised intracellular transfer protein. To verify the results obtained with purified plasma PLTP, recombinant PLTP produced in COS-1 cells was used. The transfer rates were determined by monitoring the transfer of fluorescent, pyrene-labeled phospholipids from quenched donor phospholipid vesicles to HDL3 particles. When the length of the pyrene-labeled acyl chain was varied from 6 to 14 carbons, a fairly monotonous decrease in the transfer rate was observed. No difference in rate was observed for the isomers having the pyrene-labeled and unlabeled acyl chains in reversed positions. PLTP mediated equally the transfer of the various headgroup derivatives except phosphatidylethanolamine (PE), which was transferred 2-3-fold more slowly. In all experiments the plasma and recombinant PLTP behaved identically. The specificity patterns observed for PLTP and ns-LTP were very similar. No PLTP-phospholipid intermediate could be observed, indicating that PLTP, like ns-LTP, does not form a tight complex with the lipid substrate and may thus mediate the transfer of phospholipid via another, yet unspecified mechanism.

Animals↗