Swelling of a Lecithin Lamellar Phase Induced by Small Carbohydrate Solutes

In this paper, we consider the effect of adding small carbohydrate solutes (small sugars) to DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine) L_α dispersions and the consequences on the force balance at zero osmotic pressure (maximal swelling). We show the importance of long incubations required to obtain samples at thermodynamic equilibrium where molecular diffusion has been completed. The monotonic increase of maximal swelling versus sugar content occurs as a combined effect of the screening of the van der Waals contribution and fluctuations in the lamellar stacks. According to this new approach, it is shown that changes in dielectric properties result in a much less pronounced effect than entropic forces (undulations) generated by the softening of the membranes at high sugar content. However, this sugar-induced swelling cannot be explained quantitatively by adding an entropic contribution to molecular interactions. Quantitative disagreement between the proposed mechanism and our observations is due either to nonadditivity of molecular interactions with entropic forces or to the relation used to account for the entropic contribution.     

Influence of Electrolytes on the Thicknesses of the Phospholipid Bilayers of Lamellar Lecithin Mesophases

Over a wide range of water contents, aqueous lecithin-water mixtures are mesophases in which lecithin bilayers alternate with water layers. This paper reports on low-angle X-ray diffraction measurements of the effects of electrolytes, at 1.0 N concentration, on the thicknesses of the bilayers in mesophases formed by the synthetic lecithin: 1-octadec-9-enyl-2-hexadecylglycerophosphocholine. With solutions of LiCl, NaCl, Na₂SO₄, KCl, and CsCl, the bilayer thicknesses are less than with pure water. The maximum reduction in bilayer thickness with these electrolytes is about 10% and occurs with mesophases of high content of KCl and CsCl solutions. With HCl solutions the bilayer thicknesses are about 5% greater than with pure water, and with CaCl₂ solutions the bilayer thicknesses are about the same as with pure water. The maximum amount of solution which can be mixed with lecithin before a second, purely aqueous phase is formed is also affected by electrolytes, the order for the various 1.0 N solutions being CsCl = KCl > NaCl > Na₂SO₄ > (pure water) = LiCl > CaCl₂.     

Lecithin cholesterol acyltransferase

Cholesterol transport in circulation and its removal from tissues depends on the activity of lecithin cholesterol acyltransferase (LCAT). LCAT is a soluble enzyme that converts cholesterol and phosphatidylcholines (lecithins) to cholesteryl esters and lyso-phosphatidylcholines on the surface of high-density lipoproteins. This review presents key background information and recent research advances on the structure of human LCAT, its reactions and substrates, and the expression of the LCAT gene. While the three-dimensional structure of LCAT is not yet known, a partial model now exists that facilitates the study of structure-function relationships of the native enzyme, and of natural and engineered mutants. The LCAT reaction on lipoproteins consists of several steps, starting with enzyme binding to the lipoprotein/lipid surface, followed by activation of LCAT by apolipoproteins, binding of lipid substrates and the catalytic steps giving rise to the lipid products. Quantitative data are presented on the kinetic and equilibrium constants of some of the LCAT reaction steps. Finally, overexpression of the human LCAT gene in mice and rabbits has been used to examine the physiologic role of LCAT in vivo and its protective effect against diet induced atherosclerosis.     

Quantitation of Serum Phospholipase A2 By Enzyme-Diffusion in Lecithin Agar Gels

A sensitive gel-diffusion assay for determination of phospholipase A2 was developed. PLA2 standards, serum, faecal and pancreas homogenate samples with PLA2-activity were allowed to diffuse from wells into agar-gels containing lecithin-membranes. The turbidity cleared radially upon PLA2-activity. The diameters of the cleared zones showed a linear relationship with the log of the enzyme concentration. Serum samples resulted in some turbidity within the cleared zones. This interference originating from serum lipoproteins could be abolished by hydrophobic absorption. The gel-diffusion method was compared with two other methods for PLA2, titrimetric and radiometric techniques. Analysis on 37 human patients with acute pancreatitis showed close interrelationship between these methods. The phospholipase A2 activity in sera from man, the dog, the horse, the cow, the pig and the cat were almost equal, but much less than in the albino rat. No significant differences between PLA2 activities in pancreatic samples were obtained in different animal species. Of the faecal samples, the cow had the lowest PLA2 activity. Dogs suffering from pancreatic degenerative atrophy (PDA), had significantly reduced PLA2 activity both in their pancreas and faeces but not in serum.     

Isolation of Lamellar Aggregates of the Light-Harvesting Chlorophyll a/b Protein Complex of Photosystem II with Long-Range Chiral Order and Structural Flexibility

Isolation of LHCII, the light-harvesting chlorophyll a/b complex of photosystem II, based on the procedure described by Krupaet al.(1987,Plant Physiol.84, 19–24), was optimized for obtaining purified lamellar aggregates with long-range chiral order and structural flexibility (the capability of undergoing light-induced reversible structural changes). By varying the concentration of the detergent Triton X-100 for the solubilization of thylakoid membranes, we obtained four types of LHCII aggregates: (i) With low detergent concentration, ≤0.6% (v/v), the aggregates contained lipids in high amount. These preparations with Chl a/b ratios of about 1.4 contained minor antenna complexes with a fingerprint of an additional CD band at (+) 505 nm; they formed disordered lamellae and exhibited no or weak psi-type CD bands (psi, polymerization- or salt-induced), which did not possess the ability to undergo light-induced changes (ΔCD). (ii) At the optimal concentration, around 0.7 ± 0.1% (v/v), the detergent removed some lipids and most of the minor complexes, and the Chl a/b ratio dropped to 1.0–1.1. LHCII formed loosely stacked two-dimensional lamellae which exhibited psi-type CD bands and large light-induced reversible structural changes (ΔCD). (iii) At detergent concentration above the optimum, around 0.8–1% (v/v), the lipid content of LHCII decreased and minor complexes could not be detected. LHCII formed disordered aggregates and showed neither psi-type CD nor ΔCD. (iv) High concentrations (≥1.1% (v/v)) Triton X-100 led to very pure but largely delipidated samples assembled into tightly stacked three-dimensional lamellar structures with intense psi-type CD but no ΔCD.     

Lecithin retinol acyltransferase forms functional homodimers

Membrane-bound lecithin retinol acyltransferase (LRAT), an essential enzyme in vitamin A processing, catalyzes the formation of retinyl esters from vitamin A and lecithin. Cloned and expressed LRAT has a molecular mass of 25.3 kDa. The enzyme is not homologous to known enzymes and is, therefore, of substantial interest mechanistically. Along these lines, the functional protomeric state of LRAT is of importance. Gel electrophoretic studies on LRAT in the presence of SDS and disulfide reducing agents show the expected 25 kDa monomer. However, gel electrophoresis in the absence of a reducing agent and/or strong denaturing conditions reveals substantial dimer formation. LRAT monomers can be efficiently and irreversibly cross-linked by thiol reactive bismaleimides in retinal pigment epithelial (RPE) membranes generating LRAT homodimers. Cross-linked LRAT homodimers are fully active catalytically. The experiments suggest that LRAT monomers interact in membranes and form functional homodimers through protein-protein interactions and disulfide bond formation.     

大豆卵磷脂对小鼠的抗疲劳和抗氧化作用研究

目的:研究大豆卵磷脂的抗疲劳及抗氧化作用。方法:小鼠经口给予大豆卵磷脂30天后,采用负重游泳实验,观察记录小鼠游泳死亡时间;检测血清尿素氮、肝糖原;测定血清和肝匀浆超氧化物歧化酶(SOD)活性、谷胱甘肽过氧化物酶(GSH-Px)活力、丙二醛(MDA)含量。结果:给予大豆卵磷脂后,与对照组相比,实验组小鼠负重游泳时间明显延长,肝糖原消耗量减少,降低运动后血清尿素氮水平(P<0.05);升高小鼠血清和肝匀浆SOD活性及GSH-Px活力,降低MDA的含量(P<0.05)。结论:大豆卵磷脂具有抗疲劳和抗氧化作用。     

Modification of Tobacco Mosaic Virus by Polyornithine and Lecithin

Combined action of polyornithine and lecithin modified tobacco mosaic virus (TMV) virions making them sensitive to ribonuclease (RNase), pronase or Triton X-100. Sedimentational analysis and examination of the fluorescence spectrum revealed that the reaction product obtained after RNase treatment of modified TMV was a three-component complex made of coat protein, polyornithine and lecithin. The minimum requirement for the modification was completely fulfilled by cetyltrimethylammonium bromide, suggesting that a positively charged nitrogen group and an alkyl group of moderate size, C_10–18, are necessary components. These components react with the surface region of TMV which is considered to have an important role in connecting coat protein subunits in TMV virions.     

大豆卵磷脂对小鼠的抗疲劳和抗氧化作用研究

目的：研究大豆卵磷脂的抗疲劳及抗氧化作用。方法：小鼠经口给予大豆卵磷脂30天后,采用负重游泳实验,观察记录小鼠游泳死亡时间;检测血清尿素氮、肝糖原;测定血清和肝匀浆超氧化物歧化酶（SOD）活性、谷胱甘肽过氧化物酶（GSH—Px）活力、丙二醛（MDA）含量。结果：给予大豆卵磷脂后,与对照组相比,实验组小鼠负重游泳时间明显延长,肝糖原消耗量减少,降低运动后血清尿素氮水平（P〈0．05）;升高小鼠血清和肝匀浆SOD活性及GSH-Px活力,降低MDA的含量（P〈0．05）。结论：大豆卵磷脂具有抗疲劳和抗氧化作用。     

A Nanocapsule Based on Natural Mineral Clinoptilolite Surrounded by a Lecithin Envelope

Biophysics - A technology for obtaining nanoparticles of natural clinoptilolite, a mineral from the zeolite family, under laboratory conditions has been developed. The size of zeolite particles was...     

Transverse Nuclear Relaxation in Lecithin Bilayers

IN recent months a great deal of interest has been aroused by the study of the motion of the paraffinic chains in the lyotropic mesophases of the lipid-water and soap-water systems^1–6. Apart from being interesting in themselves, such systems can eventually lead to a better understanding of the structure and function of biological membranes. For this reason, the lecithin-water system has received special attention⁷.     

卵磷脂的提纯、鉴定及应用

以大豆油脚为原料 ,采用适合于大量制备和实验室少量制备的全溶剂法 ,无机盐复合沉淀法和柱层析法 ,提取高纯度的卵磷脂 ,通过薄层层析 ,紫外光谱 ,红外光谱分析和HPLC等方法对其进行鉴定 ,并叙述了卵磷脂的应用价值。     

Elastic Torques about Membrane Edges: A Study of Pierced Egg Lecithin Vesicles

The shape of mechanically pierced giant vesicles is studied to obtain the elastic modulus of Gaussian curvature of egg lecithin bilayers. It is argued that such experiments are governed by an apparent modulus, ¯κ_app, not the true modulus of Gaussian curvature, ¯κ. A theory of ¯κ_app is proposed, regarding the pierced bilayer vesicle as a closed monolayer vesicle. The quantity measured, i.e. ¯κ_app/κ, where κ is the rigidity, agrees satisfactorily with the theory. We find ¯κ_app = -(1.9 ± 0.3) · 10^-12 erg (on the basis of κ = (2.3 ± 0.3) · 10^-12 erg). The result may have implications for bilayer fusion.