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PubMed2005

Lipid synthesis inhibitors: effect on epidermal lipid conformational changes and percutaneous permeation of levodopa.

A combination of lipid synthesis inhibitors was used to enhance the in vitro and in vivo permeation of levodopa (LD) across rat epidermis, and their influence on epidermal lipids was investigated using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. Rat epidermis was treated with ethanol and a combination of atorvastatin (750 microg/7 cm2), cerulenin (20 microg/7 cm2), and beta-chloroalanine (600 microg/7 cm2) for sustaining the reduced content of epidermal cholesterol, fatty acids (as triglycerides), and ceramide (as sphingosine), respectively, in viable rat skin. This treatment resulted in significant (P < .05) synthesis inhibition of skin lipids up to 48 hours and 6-fold enhancement in the in vitro permeation of LD. The effective plasma concentration of LD was achieved within 1 hour and maintained over 48 hours after topical application to rat epidermis treated with a combination of these lipid synthesis inhibitors. ATR-FTIR studies of inhibitor(s)-treated rat epidermis revealed a significant decrease (P < .05) in peak height and area for both asymmetric and symmetric C-H stretching absorbances, suggesting extraction of lipids. However, an insignificant (P < .05) shift in the frequency of these peaks suggested no fluidization of epidermal lipids by lipid synthesis inhibitors. A direct correlation was observed between epidermal lipid synthesis inhibition, decrease in peak height or area, and percutaneous permeation of LD. Skin lipid synthesis inhibition by a combination of lipid synthesis inhibitors seems to offer a feasible approach for enhancing the transcutaneous delivery of LD.

Administration, Topical↗
PubMed2004

DNA release from lipoplexes by anionic lipids: correlation with lipid mesomorphism, interfacial curvature, and membrane fusion.

DNA release from lipoplexes is an essential step during lipofection and is probably a result of charge neutralization by cellular anionic lipids. As a model system to test this possibility, fluorescence resonance energy transfer between DNA and lipid covalently labeled with Cy3 and BODIPY, respectively, was used to monitor the release of DNA from lipid surfaces induced by anionic liposomes. The separation of DNA from lipid measured this way was considerably slower and less complete than that estimated with noncovalently labeled DNA, and depends on the lipid composition of both lipoplexes and anionic liposomes. This result was confirmed by centrifugal separation of released DNA and lipid. X-ray diffraction revealed a clear correlation of the DNA release capacity of the anionic lipids with the interfacial curvature of the mesomorphic structures developed when the anionic and cationic liposomes were mixed. DNA release also correlated with the rate of fusion of anionic liposomes with lipoplexes. It is concluded that the tendency to fuse and the phase preference of the mixed lipid membranes are key factors for the rate and extent of DNA release. The approach presented emphasizes the importance of the lipid composition of both lipoplexes and target membranes and suggests optimal transfection may be obtained by tailoring lipoplex composition to the lipid composition of target cells.

Anions↗
PubMed2005

Simulation studies of protein-induced bilayer deformations, and lipid-induced protein tilting, on a mesoscopic model for lipid bilayers with embedded proteins.

Biological membranes are complex and highly cooperative structures. To relate biomembrane structure to their biological function it is often necessary to consider simpler systems. Lipid bilayers composed of one or two lipid species, and with embedded proteins, provide a model system for biological membranes. Here we present a mesoscopic model for lipid bilayers with embedded proteins, which we have studied with the help of the dissipative particle dynamics simulation technique. Because hydrophobic matching is believed to be one of the main physical mechanisms regulating lipid-protein interactions in membranes, we considered proteins of different hydrophobic length (as well as different sizes). We studied the cooperative behavior of the lipid-protein system at mesoscopic time- and lengthscales. In particular, we correlated in a systematic way the protein-induced bilayer perturbation, and the lipid-induced protein tilt, with the hydrophobic mismatch (positive and negative) between the protein hydrophobic length and the pure lipid bilayer hydrophobic thickness. The protein-induced bilayer perturbation was quantified in terms of a coherence length, xi(P), of the lipid bilayer hydrophobic thickness profile around the protein. The dependence on temperature of xi(P), and the protein tilt-angle, were studied above the main-transition temperature of the pure system, i.e., in the fluid phase. We found that xi(P) depends on mismatch, i.e., the higher the mismatch is, the longer xi(P) becomes, at least for positive values of mismatch; a dependence on the protein size appears as well. In the case of large model proteins experiencing extreme mismatch conditions, in the region next to the so-called lipid annulus, there appears an undershooting (or overshooting) region where the bilayer hydrophobic thickness is locally lower (or higher) than in the unperturbed bilayer, depending on whether the protein hydrophobic length is longer (or shorter) than the pure lipid bilayer hydrophobic thickness. Proteins may tilt when embedded in a too-thin bilayer. Our simulation data suggest that, when the embedded protein has a small size, the main mechanism to compensate for a large hydrophobic mismatch is the tilt, whereas large proteins react to negative mismatch by causing an increase of the hydrophobic thickness of the nearby bilayer. Furthermore, for the case of small, peptidelike proteins, we found the same type of functional dependence of the protein tilt-angle on mismatch, as was recently detected by fluorescence spectroscopy measurements.

Computer Simulation↗
PubMedDate not supplied

Determination of total lipid and lipid subclasses in meat and meat products.

Current interest in physiological and nutritional activities of the sterol, polyunsaturated fatty acid, and polar lipid fractions of meats and other foods indicates that analytical methods for lipids should be evaluated on their ability to recover and quantitate these classes. Current methods of lipid isolation furnish an extract that is dependent on the solvent(s) used, the type of food material, the temperature of extraction, and the relative proportions of the lipid classes present. Extraction with ethers or other relatively nonpolar solvents removes principally the neutral fats and nonpolar lipids. For an approximation of the crude fat content, such extraction is often sufficient, because the nonpolar fraction generally constitutes over 90% of the total lipids present. The polar lipids include the biochemically important (omega-3) and (omega-6) polyunsaturated fatty acid classes; thus, the method of lipid extraction of food products becomes relevant for a more complete and valuable characterization of their nutritional value. The various methods of lipid determination for meat products are examined for their total recovery of these important lipid groups. A sequential extraction in conjunction with subsequent analytical methods is recommended.

Animals↗
PubMed1997

Evidence that mobile lipids detected in rat brain glioma by 1H nuclear magnetic resonance correspond to lipid droplets.

Mobile lipids have been detected by proton nuclear magnetic resonance (NMR) in animal and human tumors (cultured cells, biopsies, and in vivo), but their origin and subcellular location are still unclear. They have been associated with malignancy, metastatic ability, drug resistance, and necrosis. We wanted to determine whether these lipids are located within plasma membrane microdomains or in lipid droplets for a C6 cell-induced rat glioma. NMR-visible mobile lipids were found in all subcellular fractions isolated from the rat tumor, except in the cytosolic supernatants. Transmission electron microscopy showed that lipid droplets were present in all subcellular fractions containing NMR-visible lipids and in the necrotic and perinecrotic areas of the tumor. The mean diameter of droplets isolated by flotation in the subcellular fractionation protocol was 0.97 microm (n = 682; droplet profile diameter range between 0.2 and 5.0 microm). The apparent diffusion coefficient for these lipids (46 +/- 17 microm2 s(-1) measured in vivo by proton spectroscopy was four orders of magnitude higher than would be expected if mobile lipids were inside plasma membrane microdomains. The combined results demonstrated that mobile lipids detected in vivo by proton NMR in the C6 rat glioma are located in large lipid droplets, associated with the necrotic process.

Animals↗
PubMed1998

Relationship between serum parathyroid hormone levels and lipid profile in hemodialysis patients. Evolution of lipid parameters after parathyroidectomy.

To determine the influence of parathyroid hormone (PTH) on lipid disturbances of uremia, the lipid profile was determined in 34 hemodialysis (HD) patients, comparing lipid parameters among subjects classified according to their intact PTH level. Furthermore, the effect of correction of severe secondary hyperparathyroidism on serum lipids was evaluated in 7 patients after parathyroidectomy. Total cholesterol, high-density lipoproteins (HDL), triglycerides, apolipoproteins A-I and B-100 (Apo B and Apo B), lipoprotein(a) and the ratios of cholesterol/HDL and Apo A/Apo B were analyzed. There was no correlation between serum lipids and PTH levels in the total group. Lipid profile was similar among patients classified according to their PTH level. No correlations were observed in either group between lipids and PTH. Lipid profile did not change in the seven patients with severe secondary hyperparathyroidism after parathyroidectomy. In conclusion, there was no relationship between PTH and lipids and risk ratios in HD patients. Lipid profile did not change in patients with severe secondary hyperparathyroidism after parathyroidectomy. These findings suggest that PTH does not play a significant role in the dyslipidemia of renal failure.

Adult↗
PubMedDate not supplied

Differentiation of adrenal adenomas (lipid rich and lipid poor) from nonadenomas by use of washout characteristics on delayed enhanced CT.

BACKGROUND: We describe nonenhanced, early contrast-enhanced, and delayed contrast-enhanced computed tomographic (CT) features and contrast washout characteristics of lipid-poor and lipid-rich adrenal adenomas and nonadenomas to determine the role of these methods in distinguishing one type from the other. METHODS: Sixty-five patients with 77 adrenal masses (16 lipid-poor and 37 lipid-rich adenomas and 24 nonadenomas) were consecutively examined with dynamic helical CT. Nonenhanced CT was followed by early enhanced CT at 5, 10, 15, and 30 min delays after administration of contrast material. RESULTS: The difference between the mean nonenhanced and early contrast-enhanced values of the lipid-poor adenomas and nonadenomas was statistically significant, but the ranges of the values were overlapping. The lipid-poor adenomas had lower mean attenuation values than those of nonadenomas on delayed contrast-enhanced scans at each delay time, but these differences did not reach statistical significance. Even though the relative percentage washout of the lipid-poor adenomas was lower than that of lipid-rich adenomas, it was remarkably different from that of the nonadenomas. CONCLUSIONS: The absolute or relative percentage washout of contrast material on delayed contrast-enhanced CT is a highly specific test for the differentiation of lipid-poor and lipid-rich adrenal adenomas from adrenal nonadenomas.

Adenoma↗
PubMed2004

Assessment of lipid and essential fatty acids requirements of black seabream (Spondyliosoma cantharus) by comparison of lipid composition in muscle and liver of wild and captive adult fish.

The primary aim of the present study was to compare the contents of total lipid, lipid classes and their associated fatty acids in muscle and liver of wild and one-year captive black seabream (Spondyliosoma cantharus) adults, in order to elucidate the lipid and fatty acids requirements of this fish species of potential interest for aquaculture. The total lipid contents (TL) of muscle and liver of the captive fish were 2.5-fold greater than those of the wild fish. In consequence, contents of triacylglycerols were much higher in tissues of the captive fish. Distribution of fatty acids in total lipids and lipid classes of muscle and liver was also different between both groups of fish. For instance, percentages of 20:4n-6, 20:5n-6 and 22:6n-3 were considerably higher in the wild fish, whereas 18:1, 20:1, and 22:1n-9 as well as 18:2n-6 and 20:5n-3 were more abundant in the captive fish. These results suggest that the lipid composition of the commercial diet supplied to the captive black seabream differed greatly from that of the diet consumed by the fish in the wild, which hypothetically contains the desirable composition for the lipid nutrition of this fish species. Despite the good growth and survival achieved by the black seabream after one year in captivity, the significant accumulation of lipids and the imbalance of essential fatty acids in their muscle and livers, together with the absence of spawning, suggest that future research on the lipid requirements of this omnivorous species is necessary in order to establish whether the administration of currently available aquaculture formulated feeds is adequate for good black seabream performance and reproduction.

Animals↗
PubMed2004

Murine synaptosomal lipid raft protein and lipid composition are altered by expression of human apoE 3 and 4 and by increasing age.

Apolipoprotein E (apoE) 4 and aging are risk factors for Alzheimer's disease (AD). Mice expressing human apoE4 and aged wild-type mice show a similarity in the transbilayer distribution of cholesterol in synaptic plasma membranes (SPMs) but differ markedly compared with apoE3 mice and young mice. The largest changes in cholesterol distribution were observed in the SPM exofacial leaflet where there was a doubling of cholesterol. Lipid rafts are thought to be associated with the exofacial leaflet, and we proposed that lipid raft protein and lipid composition would be associated with apoE genotype and age. Lipid rafts were isolated from synaptosomes of different age groups (2, 12, 24 months) of mice expressing human apoE3 and apoE4. Lipid raft markers, alkaline phosphatase (ALP), flotillin-1, cholesterol and sphingomyelin (SM) were examined. Lipid rafts of young apoE4 mice were more similar to older mice as compared with young apoE3 mice in reductions in alkaline phosphatase activity and flotillin-1 abundance. Lipid raft cholesterol and sphingomyelin levels were not significantly different between the young apoE3 and apoE4 mice but cholesterol levels of lipid rafts did increase with age in both genotypes. Results of the present study demonstrate that the two risk factors for Alzheimer's disease, apoE4 genotype and increasing age have similar effects on brain lipid raft protein markers and these findings support the notion that the transbilayer distribution of cholesterol is associated with lipid raft function.

Aging↗
PubMed2001

Lipid membrane expansion and micelle formation by polymer-grafted lipids: scaling with polymer length studied by spin-label electron spin resonance.

Spin-label electron spin resonance (ESR) spectroscopy and auxiliary optical density measurements are used to study lipid dispersions of N-poly(ethylene glycol)-dipalmitoyl phosphatidylethanolamine (PEG:5000-DPPE) mixed with dipalmitoyl phosphatidylcholine (DPPC). PEG:5000-DPPE bears a large hydrophilic polymer headgroup (with approximately 114 oxyethylene monomers) and is commonly used for steric stabilization of liposomes used in drug delivery. Comparison is made with results from mixtures of DPPC with polymer lipids bearing shorter headgroups (approximately 45 and 8 oxyethylene monomers). ESR spectra of phosphatidylcholine spin-labeled on the 5-C atom position of the sn-2 chain are shown to reflect the area expansion of the lipid membranes by the lateral pressure exerted in the polymer brush, in a way that is consistent with theory. The lipid chain packing density at the onset of micelle formation is the same for all three PEG-lipids, although the mole fraction at which this occurs differs greatly. The mole fraction at onset scales inversely with the size of the polymer headgroup, where the experimental exponent of 0.7 is close to theoretical predictions (viz. 0.55-0.6). The mole fraction of PEG-lipid at completion of micelle formation is more weakly dependent on polymer size, which conforms with theoretical predictions. At high mole fractions of PEG:5000-DPPE the dependence of lipid packing density on mole fraction is multiphasic, which differs qualitatively from the monotonic decrease in packing density found with the shorter polymer lipids. Lipid spin-label ESR is an experimental tool that complements theoretical analysis using polymer models combined with the lipid equation of state.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1995

Lipoxygenase-catalyzed oxygenation of storage lipids is implicated in lipid mobilization during germination.

The etiolated germination process of oilseed plants is characterized by the mobilization of storage lipids, which serve as a major carbon source for the seedling. We found that during early stages of germination in cucumber, a lipoxygenase (linoleate: oxygen oxidoreductase, EC 1.13.11.12) form is induced that is capable of oxygenating the esterified fatty acids located in the lipid-storage organelles, the so-called lipid bodies. Large amounts of esterified (13S)-hydroxy-(9Z,11E)-octadecadienoic acid were detected in the lipid bodies, whereas only traces of other oxygenated fatty acid isomers were found. This specific product pattern confirms the in vivo action of this lipoxygenase form during germination. Lipid fractionation studies of lipid bodies indicated the presence of lipoxygenase products both in the storage triacylglycerols and, to a higher extent, in the phospholipids surrounding the lipid stores as a monolayer. The degree of oxygenation of the storage lipids increased drastically during the time course of germination. We show that oxygenated fatty acids are preferentially cleaved from the lipid bodies and are subsequently released into the cytoplasm. We suggest that they may serve as substrate for beta-oxidation. These data suggest that during the etiolated germination, a lipoxygenase initiates the mobilization of storage lipids. The possible mechanisms of this implication are discussed.

Journal Article↗
PubMed2005

Lipid-modifying therapy and attainment of cholesterol goals in Europe: the Return on Expenditure Achieved for Lipid Therapy (REALITY) study.

BACKGROUND: Few studies have been conducted in actual clinical practice settings to evaluate the ways in which dyslipidemia is managed using lipid-modifying therapies. OBJECTIVE: To determine lipid-modifying therapy practices and their effects on low-density lipoprotein cholesterol (LDL-C) and/or total cholesterol (TC) goal attainment in Europeans based on prevailing guidelines at the time of therapy in each country. METHODS: Retrospective cohort analysis involving 58,223 patients initiated on lipid-modifying therapies in 10 European countries, with a median patient follow-up on lipid-modifying therapy of 15.3 months. Data on prescriptions of lipid-modifying therapies, laboratory data including LDL-C and TC, achievement of cholesterol goals for LDL-C and/or TC, and hospitalizations were obtained from healthcare administrative databases and/or patient chart reviews. RESULTS: Across Europe, statin monotherapy was the initial lipid-modifying treatment in 51,786 (89.3%) of 58,009 patients with available data. In addition, 38,853 (89.5%) of 43,410 patients with available follow-up statin potency data were initiated on statin regimens of medium or lower equipotency. Low-equipotency regimens include atorvastatin 5 mg, simvastatin 10 mg, and pravastatin 20 mg, whereas medium-equipotency regimens include atorvastatin 10 mg, simvastatin 20 mg, and pravastatin 40 mg. Regimens were adjusted to higher equipotency via either up-titration or switches to combination regimens in 16.2% of patients. On average, 40.5% of patients across Europe who were not initially at guideline recommended cholesterol goals (either LDL-C or TC) and had follow-up data attained recommended cholesterol levels, including <30% of patients in Spain, Italy, or Hungary. In many countries, the likelihood of goal attainment was inversely associated with baseline cardiovascular risk and/or LDL-C levels. CONCLUSIONS: Lipid management strategies in Europe during the study period were dominated by statin monotherapy. Even after prolonged follow-up on lipid-modifying therapy, approximately 60% of Europeans studied did not achieve guideline recommended cholesterol goals. Future emphasis must be placed on subsequent lipid panel monitoring, as well as the use of more efficacious, well-tolerated lipid-modifying therapies such as dual cholesterol inhibitors to enable more European patients to attain their recommended cholesterol goals.

Aged↗
PubMed2002

Plasma fibronectin level and its relationships with lipids, lipoproteins and C-reactive protein in patients with dyslipidaemia during lipid-lowering therapy.

OBJECTIVES: The purpose of this study is to determine plasma fibronectin level and its relationships with plasma lipids, lipoproteins and C-reactive protein (CRP) levels in patients with dyslipidaemia during lipid-lowering therapy. METHODS: Plasma levels of fibronectin, CRP, fibrinogen, lipids and lipoproteins in 38 patients with dyslipidaemia were determined before and after lipid-lowering therapy by using atorvastatin, 10 mg/day. RESULTS: After lipid-lowering therapy, serum levels of fibronectin and CRP were found to be significantly decreased by 30.4% and 43.6%, respectively, while fibrinogen levels were increased 11.7% in patients with dyslipidaemia. Before the treatment, fibronectin was found to be positively correlated with CRP and total cholesterol (r=0.38, p<0.05 and r=0.33, p<0.05, respectively) and negatively correlated with high-density lipoprotein cholesterol (HDL-C) (r=-0.42, p<0.01) in patients with dyslipidaemia. High fibronectin levels (0.57 +/- 0.17 g/l) were found in patients with HDL-C below 35 mg/dl (0.57 +/- 0.09 g/l), compared to patients with HDL-C above 35 mg/dl (0.45 +/- 0.11 g/l). During the lipid-lowering therapy, total cholesterol, low-density lipoprotein cholesterol (LDL-C), triglyceride and apo B levels were reduced while HDL-C and apo AI levels were increased. CONCLUSIONS: It was found that plasma fibronectin and CRP levels were decreased by lipid lowering therapy. Plasma fibronectin levels were associated with lipids, lipoproteins, CRP levels before treatment and these relationships disappeared after treatment. Consequently, it was suggested that reduction of plasma fibronectin levels, together with lipids and loss of its relationship with CRP, may play a role on the antiatherogenic effects of lipid-lowering therapy.

Adult↗
PubMed1992

Value of lipid- and water-suppression MR images in distinguishing between blood and lipid within ovarian masses.

The distinction between blood and lipid in ovarian masses on MR imaging is important in the differential diagnosis of these lesions. However, this is often difficult on routine MR images because both blood and lipid within tumors can have the same signal intensity as subcutaneous fat. Accordingly, we studied the value of lipid- and water-suppression MR images in making this distinction in 16 patients (21 lesions). As proved by surgery (six patients) or laparoscopy (10 patients), there were 16 endometriomas, one hemorrhagic leiomyosarcoma, and four lipid-containing mature cystic teratomas. The signal intensity in all 17 hemorrhagic lesions was greater than that of subcutaneous fat on lipid-suppression images and less than that of fat on water-suppression images. This compared with the signal intensity of the four lesions that contained lipid, in which the signal intensity was similar to that of subcutaneous fat on both the lipid- and water-suppression images. Thus, the lipid- and water-suppression MR images allowed an accurate distinction between the two. Our experience suggests that the appearance of blood and lipid in ovarian tumors is sufficiently different on lipid- and water-suppression MR images to allow an accurate distinction between the two. The two techniques should be useful in the differential diagnosis of such lesions by MR imaging.

Adipose Tissue↗
PubMed1980

The partition of cis-parinaric acid and trans-parinaric acid among aqueous, fluid lipid, and solid lipid phases.

In this article, I review the current information concerning the partition of the fluorescent probes, cis-parinaric acid (9, 11, 13, 15-cis, trans, trans, cis-octadecatetraenoic acid) and trans-parinaric acid (9, 11, 13, 15-all trans-octadecatetraenoic acid) among aqueous, solid lipid, and fluid lipid phases. The association of these probes with lipid is described by a mole fraction partition coefficient whose value is trypically in the range of 1-5 x 10(6), a reasonable value in light of partition coefficients for other fatty acids between hydrophobic phases and water. The partition coefficient, in the absence of lipid phase changes, is relatively independent of temperature and only slightly dependent on the total aqueous probe concentration. In lipid samples which contain coexisting fluid and solid phases, trans-parinaric acid preferentially partitions into the solid phase, while cis-parinaric acid distributes nearly equally between fluid and solid phases. This partition behavior probably arises from the molecular shape of the cis and trans parinaric acid in mixed lipid systems or membranes it is possible to evaluate the proportion of lipid components involved in phase changes or phase separation. From fluorescence energy transfer between protein typtophan residues and the parinaric acid isomers it is possible to gain information about the organization of lipids and proteins in membranes and model systems. I close the review by considering some of the membrane research areas where these probes and their various lipid derivatives may be particularly useful.

Chemical Phenomena↗
PubMed1991

Interaction between dietary proteins and lipids in the regulation of serum and liver lipids in the rabbit. Effect of fish protein.

Purified diets varying in dietary protein, namely casein (CA), soy protein (SP), fish protein (FP), and lipid origin (corn oil (CN), coconut oil (CO)) were fed to rabbits to evaluate the effects of protein and fat source, as well as protein-lipid interactions, on serum total, lipoprotein and hepatic lipid levels. Dietary proteins and lipids exerted a separate effect on serum total cholesterol (C), very low-density lipoprotein cholesterol (VLDL-C), and low-density lipoprotein cholesterol to high density lipoprotein cholesterol (LDL-C/HDL-C) ratio. Hence, CA increased serum cholesterol compared to SP, while coconut oil enhanced serum and VLDL-C, and decreased LDL-C/HDL-C compared to corn oil. Dietary proteins interacted with dietary lipids to modulate HDL-C levels. Thus, FP maintained a high level of HDL-C regardless of lipid origin, compared to CA and SP whose HDL-C levels were decreased by corn oil, compared to coconut oil. A dietary protein-lipid interaction was also observed in the regulation of liver cholesterol levels. Coconut oil, compared to corn oil, decreased liver cholesterol in rabbits fed FP, whereas hepatic cholesterol concentration was unaltered by dietary lipid source in CA- and SP-fed rabbits. These results demonstrate that dietary proteins act synergistically with dietary lipids to regulate cholesterol metabolism in the rabbit.

Animals↗
PubMed2005

A molecular dynamics study of an archaeal tetraether lipid membrane: comparison with a dipalmitoylphosphatidylcholine lipid bilayer.

Molecular dynamics simulations of an archaeal membrane made up of bipolar tetraether lipids and a dipalmitoylphosphatidylcholine (DPPC) lipid membrane were performed and compared for the first time. The simulated archaeal membrane consists of a pure monolayer of asymmetrical lipids, analogous to the main polar lipid [MPL; Swain, M., Brisson, J.-R., Sprott, G.D., Cooper, F.P., and Patel, G.B., (1997) Identification of beta-L-Gulose as the Sugar Moiety of the Main Polar Lipid of Thermoplasma acidophilum, Biochim. Biophys. Acta 1345, 56-64] found in T. acidophilum, an extremophile archaeal organism. This simulated membrane lipid contains two cyclopentane rings located on one of the two aliphatic chains of the lipid. The archaeal membrane is simulated at 62degreesC, slightly above the optimal growth temperature of T. acidophilum. We compared the organization of this tetraether lipid monolayer with a DPPC bilayer simulated at 50degreesC, both of them being modeled in a partially hydrated state. Our results assess the singularity of the tetraether lipid organization, in particular the influence of the spanning structure on the molecular ordering within the archaeal membrane.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1980

Boundary lipids and protein mobility in rhodopsin-phosphatidylcholine vesicles. Effect of lipid phase transitions.

Purified rhodopsin from bovine retina has been incorporated into phospholipid bilayers. Dimiristoylphosphatidylcholine, dipalmitoylphosphatidylcholine, dioleylphosphatidylcholine and egg phosphatidylcholine were used as host lipids, with ratio of lipid to protein of 120 : 1 (mol to mol). In order to probe the lipid-protein interface specifically, a spin-labeled fatty acid was covalently bound to rhodopsin via an isocyanate reacting group. A spin-labeled phospholipid was used to probe the bulk lipidic phase while a tightly bound maleimide spin label was used to obtain the protein rotational correlation time by the saturation transfer technique. The following results were obtained: (1) The kinetics of reduction by ascorbate of the spin-labeled fatty acid covalently bound to rhodopsin demonstrate that the alkyl chain attached to the protein is positioned in the membrane in the same way as the alkyl chains of a phospholipid. (2) The EPR spectra of the latter shows two components: a strongly immobilized component and a weakly immobilized component. The ratio of the two depends upon the temperature and on the nature of the phospholipids. (3) The signal of the weakly immobilized component is compared to that obtained in the corresponding pure lipids. The latter signal, assumed to represent non-bounded lipids, indicates a sharp transition at the phospholipid phase transition with dimytristoylphosphatidylcholine or dipalmitoylphosphatidylcholine. The former signal (corresponding to the lipid-protein interface) indicates only a broad transition extending over 7 degrees C with dipalmitoylphosphatidylcholine and almost no transition with dimyristoylphosphatidylcholine. (4) In a similar way, the rotational correlation time of the protein only changes progressively when the phase transition occurs. Our interpretation of the data can be summarized as follows: The immobilized component seen by the EPR technique in the hydrophobic environment of this intrinsic protein very probably reflects protein-protein contacts and thus corresponds to hindrance of the labeled chains, when they are trapped between neighbouring proteins. Below the phase transition lipid segregation whould increase the probability of protein contact. However, over a certain range of temperature, the contact with the protein interface probably at the same time prevents the non-segregated phospholipids from feezing. The differences in the results obtained with the various phosphatidylcholines above their transition temperature suggest that the solubility of rhodopsin in bilayers depends not only on the fluidity of the lipids, but also, to some extent, on the phospholipid chain length.

Animals↗