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PubMed1982

Rabbit liver microsomal lipid peroxidation. The effect of lipid on the rate of peroxidation.

Rat and rabbit liver microsomes catalyze an NADPH-cytochrome P-450 reductase-dependent peroxidation of endogenous lipid in the presence of the chelate, ADP-Fe3+. Although liver microsomes from both species contain comparable levels of NADPH-cytochrome P-450 reductase and cytochrome P-450, the rate of lipid peroxidation (assayed by malondialdehyde and lipid hydroperoxide formation) catalyzed by rabbit liver microsomes is only about 40% of that catalyzed by rat liver microsomes. Microsomal lipid peroxidation was reconstituted with liposomes made from extracted microsomal lipid and purified protease-solubilized NADPH-cytochrome P-450 reductase from both rat and rabbit liver microsomes. The results demonstrated that the lower rates of lipid peroxidation catalyzed by rabbit liver microsomes could not be attributed to the specific activity of the reductase. Microsomal lipid from rabbit liver was found to be much less susceptible to lipid peroxidation. This was due to the lower polyunsaturated fatty acid content rather than the presence of antioxidants in rabbit liver microsomal lipid. Gas-liquid chromatographic analysis of fatty acids lost during microsomal lipid peroxidation revealed that the degree of fatty acid unsaturation correlated well with rates of lipid peroxidation.

Adenosine Diphosphate↗
PubMedDate not supplied

Lipid polymorphism and the roles of lipids in membranes.

The reasons for lipid diversity in membranes are not understood. Here we review evidence supporting the proposal that factors related to the polymorphic capabilities of lipids provide a rationale for lipid diversity. In particular, the ability of lipids to adopt different polymorphic phases appears to be related to a generalized shape property, where lipids with a cylindrical geometry preferentially adopt the bilayer phase whereas 'cone' shaped lipids adopt the hexagonal HII phase. Lipid diversity may then be considered to satisfy three demands. The first is obviously a need for bilayer forming lipids to provide the basic permeability barrier, whereas the second concerns a need for non-bilayer lipids and associated structures for fusion and related membrane contact phenomena to proceed. A third, and less obvious demand satisfied by nonbilayer lipids concerns the ability of lipids of different shapes to modulate the order in the hydrocarbon region when constrained to a bilayer organization. These possibilities are summarized in a metamorphic mosaic model of membranes.

Freeze Fracturing↗
PubMed2005

Lipoprotein-mediated lipid transport in insects: analogy to the mammalian lipid carrier system and novel concepts for the functioning of LDL receptor family members.

In all animals, lipoproteins are used to transport lipids through the aqueous circulation. Lipids are delivered to mammalian cells by two different mechanisms: via endocytic uptake of the complete lipoprotein particle mediated by members of the low density lipoprotein (LDL) receptor (LDLR) family, or by selective delivery of lipoprotein-carried lipids at the cell surface, such as lipid uptake following the action of a lipoprotein lipase. Although many structural elements of the lipid transport system of insects are similar to those of mammals, insect lipoprotein-mediated lipid transport was thought to apply only to the latter concept, since the single lipoprotein acts as a reusable lipid shuttle. However, the recent identification of lipoprotein receptors of the LDLR family in insects suggests that lipid transport in these animals may also adopt the first concept. Yet, the endocytic properties of the insect LDLR homologue appear to deviate from those of the mammalian LDLR family members, resulting in the recycling of endocytosed lipoprotein in a transferrin-like manner. This indicates that a hitherto unknown as well as unexpected function can be added to the plethora of functions of LDLR family members. Analysis of the molecular mechanism of the ligand-recycling function of the insect receptor provides also new insight into the possible functioning of the mammalian family members. In the last several years, mammalian and insect lipoprotein-mediated lipid transport systems have been reviewed separately with respect to functioning and lipid delivery. This review, in which new and important developments in the insect field with respect to our understanding of lipid delivery are discussed with a particular focus on the involvement of the LDLR homologue, aims at comparing the two systems, also from an evolutionary biological perspective, and proposes that the two systems are more similar than assumed previously.

Amino Acid Sequence↗
PubMed2006

Lipids and lipid domains in the peroxisomal membrane of the yeast Yarrowia lipolytica.

Biological membranes have unique and highly diverse compositions of their lipid constituents. At present, we have only partial understanding of how membrane lipids and lipid domains regulate the structural integrity and functionality of cellular organelles, maintain the unique molecular composition of each organellar membrane by orchestrating the intracellular trafficking of membrane-bound proteins and lipids, and control the steady-state levels of numerous signaling molecules generated in biological membranes. Similar to other organellar membranes, a single lipid bilayer enclosing the peroxisome, an organelle known for its essential role in lipid metabolism, has a unique lipid composition and organizes some of its lipid and protein components into distinctive assemblies. This review highlights recent advances in our knowledge of how lipids and lipid domains of the peroxisomal membrane regulate the processes of peroxisome assembly and maintenance in the yeast Yarrowia lipolytica. We critically evaluate the molecular mechanisms through which lipid constituents of the peroxisomal membrane control these multistep processes and outline directions for future research in this field.

Endoplasmic Reticulum↗
PubMed2006

Dietary neutral lipid level and source in Senegalese sole (Solea senegalensis) larvae: effect on growth, lipid metabolism and digestive capacity.

Contrary to larval essential fatty acid (EFA) requirements, the effect of dietary neutral lipid supply has been little investigated in marine fish larvae. The present work investigates the effect of feeding Senegalese sole larvae on Artemia enriched with higher or lower doses of lipid emulsion. Two lipid sources - soybean oil and fish oil - were compared. From 16 days after hatching (DAH) onwards, larvae were fed one of four experimental treatments: Artemia enriched on a high or low dose of soybean oil emulsion (HS and LS) or Artemia enriched on a high or low dose of fish oil emulsion (HF and LF). In terms of growth, the dietary lipid level did not have a significant effect while the soybean oil treatments induced a lower growth than the fish oil-enriched Artemia. The fatty acid (FA) composition of the larvae closely reflected the dietary quantitative and qualitative FA profile. Only slight dietary effects were noted in the activity of trypsin, lipase and alkaline phosphatase. A higher amount of lipid droplets was noticeable in the posterior intestine epithelia and in the hepatocytes of larvae fed Artemia enriched with higher lipid doses, while LS-Artemia induced the lower lipid accumulation on the basal zone of the enterocytes, in accordance with the lowest total lipid level measured in this treatment. These results suggest an important effect of dietary total lipid level on lipid accumulation in the enterocytes and on FA absorption. At 33 DAH a tube feeding trial was conducted with 14C-labelled oleic acid (OA) or triolein (TRI), showing that the lower accumulation of lipid droplets in the larvae fed LS was associated with a significantly higher absorption and retention in the gut and body tissues of the TRI label. For OA no significant differences between treatments were found. TRI label was considerably more evacuated than OA, indicating that sole larvae may have a lower capacity to incorporate a triacylglycerol, which needs to be digested. Finally, OA appears to be preferentially utilized for energy production, accumulating more in larval tissues when absorbed in higher amounts.

Animals↗
PubMed2000

Membrane dynamics as seen by fourier transform infrared spectroscopy in a cyanobacterium, Synechocystis PCC 6803. The effects of lipid unsaturation and the protein-to-lipid ratio.

The roles of lipid unsaturation and lipid-protein interactions in maintaining the physiologically required membrane dynamics were investigated in a cyanobacterium strain, Synechocystis PCC 6803. The specific effects of lipid unsaturation on the membrane structure were addressed by the use of desaturase-deficient (desA(-)/desD(-)) mutant cells (which contain only oleic acid as unsaturated fatty acid species) of Synechocystis PCC 6803. The dynamic properties of the membranes were determined from the temperature dependence of the symmetric CH(2) stretching vibration frequency, which is indicative of the lipid fatty acyl chain disorder. It was found that a similar membrane dynamics is maintained at any growth temperature, in both the wild-type and the mutant cell membranes, with the exception of mutant cells grown at the lower physiological temperature limit. It seems that in the physiological temperature range the desaturase system of the cells can modulate the level of lipid desaturation sufficiently to maintain similar membrane dynamics. Below the range of normal growth temperatures, however, the extent of lipid disorder was always higher in the thylakoid than in the cytoplasmic membranes prepared from the same cells. This difference was attributed to the considerable difference in protein-to-lipid ratio in the two kinds of membranes, as determined from the ratio of the intensities of the protein amide I band and the lipid ester C&z.dbnd6;O vibration. The contributions to the membrane dynamics of an ab ovo present 'structural' lipid disorder due to the protein-lipid interactions and of a thermally induced 'dynamic' lipid disorder could be distinguished.

Cell Membrane↗
PubMed1987

Lipid mobility and order in bovine rod outer segment disk membranes. A spin-label study of lipid-protein interactions.

Lipid-protein interactions in bovine rod outer segment disk membranes have been studied by using a series of eight stearic acid spin-label probes which were labeled at different carbon atom positions in the chain. In randomly oriented membrane dispersions, the electron spin resonance (ESR) spectra of the C-8, C-9, C-10, C-11, C-12, C-13, and C-14 atom positional isomers all apparently consist of two components. One of the components corresponds closely to the spectra obtained from dispersions of the extracted membrane lipids, and the other, which is characterized by a considerably greater degree of motional restriction of the lipid chains, is induced by the presence of the protein. Digital subtraction has been used to separate the two components. The proportion of the motionally restricted lipid component is approximately constant, independent of the position of the spin-label group, and corresponds to 30-40% of the total spin-label spectral intensity. The hyperfine splitting of the outer maxima in the difference spectra of the motionally restricted component decreases, and concomitantly, the line widths increase with increasing temperature but change relatively little with increasing distance of the spin-label group from the polar head-group region. This indicates that the corresponding chain motions of the protein-interacting lipids lie in the slow-motion regime of spin-label ESR spectroscopy (tau R approximately 10(-8) S) and that the mobility of these lipids increases with increasing temperature but does not vary greatly along the length of the chain. The data from the hyperfine splittings also suggest the existence of a polarity gradient immediately adjacent to the protein surface, as observed in the fluid lipid regions of the membrane. The more fluid lipid component is only slightly perturbed relative to the lipids alone (for label positions 5-14, inclusive), indicating the presence of chain motions on the nanosecond time scale, and the spectra also reveal a similar polarity profile in both lipid and membrane environments. ESR spectra have also been obtained as a function of magnetic field orientation with oriented membrane samples. For the C-14 atom positional isomer, the motionally restricted component is observed to have a large hyperfine splitting, with the magnetic field oriented both parallel and perpendicular to the membrane normal. This indicates that the motionally restricted lipid chains have a broad distribution of orientations at this label position.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1997

Structural analysis of apolipoprotein A-I: limited proteolysis of methionine-reduced and -oxidized lipid-free and lipid-bound human apo A-I.

The domain structures of lipid-free and lipid-bound apolipoprotein A-I (apo A-I) containing reduced and oxidized methionines were analyzed by limited proteolysis. Lipid-free apo A-I is cleaved primarily in the extreme carboxy-terminus and, to a much lesser extent, in the central region of the protein between residues 115 and 136. Oxidation of methionines 112 and 148 to the corresponding sulfoxides in putative amphipathic helices 4 (P99-E120) and 6 (P143-A164), respectively, causes helices 1 (L44-G65), 2 (P66-S87), and 7 (P165-G186) to become susceptible to protease digestion. These results are consistent with a discrete, globular tertiary structure for the lipid-free protein minimally formed from amphipathic helices 1, 2, 4, 6, and 7. In distinct contrast to lipid-free apo A-I, lipid-bound apo A-I is most susceptible to cleavage in the extreme amino-terminus and, to a lesser extent, in both the central and carboxy-terminal regions. The observed cleavage pattern for the reduced lipid-bound protein supports the existence of many of the turns between helices predicted by sequence analysis of the lipid-bound protein. Methionine oxidation of lipid-bound protein results in a decreased protease susceptibility in the extreme amino-terminus and a concomitant increase in protease susceptibility in the central and carboxy-terminal regions. The results from methionine oxidation indicate the oxidation state of the protein is an important determinant in defining the conformation of both lipid-free and lipid-bound apo A-I.

Amino Acid Sequence↗
PubMed1997

Cationic lipid-mediated gene delivery to murine lung: correlation of lipid hydration with in vivo transfection activity.

A panel of lipidic tetraalkylammonium chlorides has been prepared and screened in studies of both lipid hydration and in vivo mouse transfection. The effect of cationic lipid structure on liposome surface hydration was determined using differential scanning calorimetry. Increases in headgroup steric bulk and the inclusion of cis-unsaturation in the hydrophobic domain led to greater lipid hydration, indicative of a decrease in lipid polar domain associations. Cationic lipids containing hydrogen-bonding functionality in the polar domain exhibited a corresponding decrease in observed lipid hydration, indicative of an increase in lipid polar domain associations. To explore a potential correlation of the hydration data with transfection activity, we examined the in vivo transfection activity of the lipid panel by direct intratracheal instillation of cationic liposome-DNA complexes into BALB/c mice. The more active transfection agents were the lipids that featured headgroup structures promoting close polar domain association in combination with fatty acyl cis-unsaturation. The hydration data suggest that the more effective transfection lipids for mouse lung delivery are those possessing the greatest imbalance between the cross-sectional areas occupied by the polar and hydrophobic domains.

Animals↗
PubMed2001

Heat stability of prion rods and recombinant prion protein in water, lipid and lipid-water mixtures.

Prion rods, i.e. insoluble infectious aggregates of the N-terminally truncated form of the prion protein, PrP 27-30, and the corresponding recombinant protein, rPrP(90-231), were autoclaved in water, bovine lipid or lipid-water mixtures for 20 min at temperatures from 100 to 170 degrees C. A protocol was developed for the quantitative precipitation of small amounts of protein from large excesses of lipid. PrP remaining undegraded after autoclaving was quantified by Western blot and degradation factors were calculated. The Arrhenius plot of the rate of degradation vs temperature yielded linear relationships for prion rods in water or lipid-water as well as for rPrP(90-231) in lipid-water. The presence of lipids increased the heat stability of prion rods, especially at lower temperatures. Prion rods had a much higher thermal stability compared to rPrP. Autoclaving of prion rods in pure lipid gave different results - not simple degradation but bands indicative of covalently linked dimers, tetramers and higher aggregates. The heat stability of prion rods in pure lipid exceeded that in lipid-water mixtures. Degradation factors larger than 10(4) were reached at 170 degrees C in the presence of lipids and at 150 degrees C in the absence of lipids. The linear correlation of the data allows cautious extrapolation to conditions not tested, i.e. temperatures higher than 170 degrees C. A factual basis for assessing the biological safety of industrial processes utilizing potentially BSE-or scrapie-contaminated animal fat is provided.

Animals↗
PubMed1976

A possible correlation between lipid hydration and lipid activation of the C55-isoprenoid alcohol phosphokinase apoprotein.

1. A direct method for determining the binding of triated water to lipids is described. The experimental conditions were practically identical to those previously employed (1974) in the determination of the cofactor activities of a series of oleyl-lipids in reactivation of the C55-isoprenoid alcohol phosphokinase apoprotein. 2. Active cofactor lipids (dioleyl lecithin, sodium oleate, 1-monoolein, 1-monomyristin)bound between 2.3 and 5.3 nmol 3H2O per nmol lipid, whereas less than 0.14 nmol 3H2O were bound per nmol of the inactive lipids (1,2- and 1,3-diolein, triolein, oleyl alcohol, methyl oleate, cholesteryl oleate). 3. When exposed to 3H2O vapour, the active lipids adsorbed between 1 and 2 nmol 3H2O per nmol lipid, whereas the inactive lipids adsorbed less than 0.1 nmol 3H2O per nmol lipid. 4. The active lipid cofactor, egg lecithin, bound more than twice as much 3H2O as egg phosphatidylethanolamine which was devoid of cofactor activity in the absence of detergent. 5. Appropriately hydrated lipid polar groups are concluded to be required for an alignment with polar amino acid side chains of the enzyme apoprotein in the formation of a mixed micellar lipoprotein complex. The enzyme reaction might occur at the resulting lipoprotein/water interface.

Apoenzymes↗
PubMed1990

Suppressive effect of lipid A partial structures on lipopolysaccharide or lipid A-induced release of interleukin 1 by human monocytes.

Experiments were designed to investigate the significance of lipid A partial structures, precursor Ia (compound 406), and lipid X (compound 401) to serve as antagonists of interleukin 1 (IL-1) release from human mononuclear cells and monocytes induced by lipopolysaccharide (LPS, endotoxin) of Salmonella abortus equi or synthetic Escherichia coli lipid A (compound 506). A definite inhibition mediated by lipid A partial structures on IL-1 release induced by LPS or lipid A was found in repeated experiments. The inhibitory effect was exerted not only on IL-1 release, but also on IL-1 peptide synthesis at the intracellular level. The results also show that lipid A partial structures have suppressive effects even when added 1-4 h after LPS or lipid A. We conclude from these results that lipid A partial structures (precursor Ia and lipid X) have potent immunomodulatory effects on LPS- and lipid A-induced IL-1 release and may become useful reagents to study the mechanism of interaction of LPS and lipid A with cells of the immune system.

Carbohydrate Sequence↗
PubMed2005

Lipids, lipases, and lipid-modifying enzymes in plant disease resistance.

Lipids and lipid metabolites influence pathogenesis and resistance mechanisms associated with plant-microbe interactions. Some microorganisms sense their presence on a host by perceiving plant surface waxes, whereas others produce toxins that target plant lipid metabolism. In contrast, plants have evolved to recognize microbial lipopolysaccharides (LPSs), sphingolipids, and lipid-binding proteins as elicitors of defense response. Recent studies have demonstrated that the plasma membrane provides a surface on which some plant resistance (R) proteins perceive pathogen-derived effectors and thus confer race-specific resistance. Plant cell membranes also serve as reservoirs from which biologically active lipids and precursors of oxidized lipids are released. Some of these oxylipins, for example jasmonic acid (JA), are important signal molecules in plant defense. Arabidopsis thaliana is an excellent model plant to elucidate the biosynthesis and metabolism of lipids and lipid metabolites, and the characterization of signaling mechanisms involved in the modulation of plant defense responses by phytolipids. This review focuses on recent studies that highlight the involvement of lipids and lipid metabolites, and enzymes involved in lipid metabolism and modification in plant disease resistance.

Lipase↗
PubMed2000

Encapsulation of plasmid DNA in stabilized plasmid-lipid particles composed of different cationic lipid concentration for optimal transfection activity.

In previous work (Wheeler et al. (1999) Gene Therapy 6, 271-281) we have shown that plasmid DNA can be entrapped in "stabilized plasmid lipid particles" (SPLP) using low levels (5-10 mol%) of cationic lipid, the fusogenic lipid dioleoylphosphatidylethanolamine (DOPE), and a polyethyleneglycol (PEG) coating for stabilization. The PEG moieties are attached to a ceramide anchor containing an arachidoyl acyl group (PEG-CerC20). However, these SPLP exhibit low transfection potencies in vitro as compared to plasmid/cationic lipid complexes formed with liposomes composed of cationic and neutral lipid at a 1:1 lipid ratio. The objective of this study was to construct SPLPs with increased cationic lipid contents that result in maximum transfection levels. A phosphate buffer detergent dialysis technique is described resulting in formation of SPLP containing 7-42.5 mol% DODAC with reproducible encapsulation efficiency of up to 80%. An octanoyl acyl group was used as anchor for the PEG moiety (PEG-CerC8) permitting a quick exchange out of the SPLP to further optimize the in vitro and in vivo transfection. We have demonstrated that this technique can be used to encapsulate either linearized DNA or supercoiled plasmids ranging from 3-20 kb. The SPLP formed could be isolated from empty vesicles by sucrose density gradient centrifugation, and exhibited a narrow size distribution of approximately 75 +/- 6 nm as determined by cryo-electron microscopy. The high plasmid-to-lipid ratio observed corresponded to one plasmid per particle. The SPLP consist of a lipid bilayer surrounding the plasmid DNA as visualized by cryo-electron microscopy. SPLP containing a range of DODAC concentrations were tested for in vitro and in vivo transfection. In vitro, in COS-7 cells transfection reached a maximum after 48 h. The transfection efficiency increased when the DODAC concentration in the SPLP was decreased from 42.5 to 24 mol% DODAC. Decreasing the cationic lipid concentration improved transfection in part due to decreased toxicity. In vivo studies using an intraperitoneal B16 tumor model and intraperitoneal administration of SPLP showed maximum transfection activity for SPLP containing 24 mol% DODAC. Gene expression observed in tumor cells was increased by approximately one magnitude as compared to cationic lipid/DNA complexes. The SPLP were stable and upon storage at 4 degrees C no significant change in the transfection activity was observed over a one-year period. Thus this phosphate buffer detergent dialysis technique can be used to generate SPLP formulations containing a wide range of cationic lipid concentrations to determine optimal SPLP composition for high transfection activity and low toxicity.

Animals↗
PubMed1975

Reactivation of the lipid-depleted pyruvate oxidase system from Escherichia coli with cell envelope neutral lipids.

The pyruvate oxidase system of Escherichia coli is composed of a soluble flavoprotein, pyruvate oxidase (EC 1.2.2.2, pyruvate:ferricytochrome b1 oxidoreductase), and an electron transport system associated with the cell envelope-membrane fraction. The membrane particles contain 15% lipid by weight. Fractionation of the lipids revealed that abut one-third are neutral lipids and two-thirds are phospholipids. The relative ratio of ubiquinone to menaquinone within the neutral lipid fraction is 15:1 on a molar basis. Removal of the lipids from the membrane particles by extraction with aqueous acetone or hydrolysis of the phospholipids by treatment with Bacillus cereus phospholipase C results in a complete loss of electron transport activity. Analysis of the particles extracted with aqueous acetone revealed that practically all the neutral lipids and 65% of the phospholipids are removed by this treatment. Phospholipase treatment results in a loss of 75% of the membrane phospholipid phosphorus; however, the diglycerides and the neutral lipids produced by phospholipase hydrolysis remain associated with the particles. Addition of neutral lipid and a detergent, hepta-DL-alanyl dodecylamide to the acetone-extracted material results in a restoration of 37% of the original particle activity. Addition of neutral lipid and hepta-DL-alanyl dodecylamide to phospholipase-treated particles completely restores the original electron transport activity. Furthermore, addition of ubiquinone from either yeast (UQ6) or E. coli (UQ8) will restore pyruvate oxidase activity when the quinones are supplemented with photoinactivated neutral lipid. No restoration of activity to phospholipase-treated particles is noted upon the addition of either menaquinone 6 or menaquinone 8 to the reconstitution system. In fact, these compounds appear to suppress restoration of activity when they are added to reaction mixtures containing neutral lipid and phospholipase-treated particles.

Cell Membrane↗
PubMed2002

Cellular lipid binding proteins as facilitators and regulators of lipid metabolism.

Evidence is accumulating that cellular lipid binding proteins are playing central roles in cellular lipid uptake and metabolism. Membrane-associated fatty acid-binding proteins putatively function in protein-mediated transmembrane transport of fatty acids, likely coexisting with passive diffusional uptake. The intracellular trafficking of fatty acids, bile acids, and other lipid ligands, may involve their interaction with specific membrane or protein targets, which are unique properties of some but not of all cytoplasmic lipid binding proteins. Recent studies indicate that these proteins not only facilitate but also regulate cellular lipid utilization. For instance, muscle fatty acid uptake is subject to short-term regulation by translocation of fatty acid translocase (FAT)/CD36 from intracellular storage sites to the plasma membrane, and liver-type cytoplasmic fatty acid-binding protein (L-FABPc) functions in long-term, ligand-induced regulation of gene expression by directly interacting with nuclear receptors. Therefore, the properties of the lipid-protein complex, rather than those of the lipid ligand itself, determine the fate of the ligand in the cell. Finally, there are an increasing number of reports that deficiencies or altered functioning of both membrane-associated and cytoplasmic lipid binding proteins are associated with disease states, such as obesity, diabetes and atherosclerosis. In conclusion, because of their central role in the regulation of lipid metabolism, cellular lipid binding proteins are promising targets for the treatment of diseases resulting from or characterised by disturbances in lipid metabolism, such as atherosclerosis, hyperlipidemia, and insulin resistance.

Animals↗
PubMed1991

Archaebacterial ether lipid diversity analyzed by supercritical fluid chromatography: integration with a bacterial lipid protocol.

A strategy has been developed for archaebacterial lipid analysis which provides three times the information to describe archaebacterial isolates and is compatible with simultaneous eubacterial/eukaryotic lipid analysis of environmental samples. Eubacterial and micro-eukaryotic biomass, community structure, and nutritional status have been routinely defined in environmental samples by lipid analysis. Lipid profiles are also useful in eubacterial identification and taxonomy. Polar lipid or whole cell ester-linked fatty acids are generally analyzed by gas chromatography-mass spectroscopy. Archaebacteria are characterized by their ether-linked membrane lipids. There is, however, less diversity in the side chains of archaebacterial membrane lipids as compared the eubacterial ester-linked membrane lipids. The information content of the archaebacterial lipid profile was increased by separately analyzing the polar lipid, glycolipid, and lipid-extracted residue fractions. Identification and quantification were performed by supercritical fluid chromatography. Results are presented for three species of methanogens and four thermoacidophile isolates, and compared with a literature review.

Archaea↗
PubMed1990

Manduca sexta lipid transfer particle acts upon a lipoprotein to catalyze lipid and apoprotein disproportionation.

A novel reaction, catalyzed by Manduca sexta lipid transfer particle (LTP), transforms low density lipophorin (LDLp) into two distinct lipoprotein species. A population of LDLp particles serves as lipid donor or acceptor in LTP-catalyzed production of a very low density lipophorin (VLDLp) and a high density lipophorin (HDLp) product. The products result from facilitated net transfer of lipid mass from donor LDLp particles to acceptor LDLp particles. Transfer of apolipophorin III (apoLp-III) from donor to acceptor lipoprotein occurs during the reaction to produce a lipid- and apoLp-III-enriched VLDLp species and lipid- and apoLp-III-depleted HDLp species. The VLDLp produced in this in vitro reaction contains more lipid and apoLp-III than any previous lipophorin species reported and further demonstrates the scope of the lipid binding capacity of lipophorin. Lipid analysis and radiolabeling studies confirmed that unidirectional net transfer of lipid mass and apoLp-III from donor to acceptor occurs. When 3H-lipid-LDLp was used as substrate in the LTP-catalyzed disproportionation reaction the density distribution of radioactivity and protein provided evidence of vectorial transfer of diacylglycerol, phospholipid, and free fatty acids. Electron micrographs of the original LDLp population and of the LTP-induced product lipoprotein population provided further support for the interpretation derived from biochemical studies. This LTP-catalyzed disproportionation was observed only with apoLp-III-rich LDLp suggesting that the presence of increased amounts of this apoprotein dramatically affects the properties of the particle and appears to be directly related to the capacity of the lipoprotein to bind lipid.

Animals↗