First integrals of the axisymmetric shape equation of lipid membranes

The shape equation of lipid membranes is a fourth-order partial differential equation.Under the axisymmetric condi-tion,this equation was transformed into a second-order ordinary differential equation(ODE)by Zheng and Liu(Phys.Rev.E 482856(1993)).Here we try to further reduce this second-order ODE to a first-order ODE.First,we invert the usual process of variational calculus,that is,we construct a Lagrangian for which the ODE is the corresponding Euler-Lagrange equation.Then,we seek symmetries of this Lagrangian according to the Noether theorem.Under a certain restriction on Lie groups of the shape equation,we find that the first integral only exists when the shape equation is identical to the Will-more equation,in which case the symmetry leading to the first integral is scale invariance.We also obtain the mechanical interpretation of the first integral by using the membrane stress tensor.

Study of Oligonucleotide Fixation on Bilayer Lipid Membranes by Patch-clamp Pipette Support

One kind of novel BLMs was fabricated by patch-clamp pipette technology characterized in considerably sensitive to changes of electrochemical parameters.Detectiye currents and voltage presented linear relationship when BLMs was formed and it could be confirmed by Gramicidin method.Ion current was increased by dihexyl (C_ (12)) modified ssDNA fixed on the BLMs and also indicated linear relationship to ssDNA's concentration due to the interaction of (C_ 12)-ssDNA and BLMs.Further more,the regression equations were different from BLMs fixed with ssDNA probe and a blank control BLM in the same experimental conditions.The ssDNA probe was successfully fixed on patch-clamp pipette supported-BLMs.Based on our studies,a biosensor with reactive element of patch-clamp pipette-supported BLMs has been established.

Challenges in the theoretical investigations of lipid membrane configurations

We report some key results in the theoretical investigations of configurations of lipid membranes and present several challenges in this field,which involve（i）the exact solutions to the shape equation of lipid vesicles,（ii）the exact solutions to the governing equations of open lipid membranes,（iii）the neck condition of two-phase vesicles in the budding state,（iv） the nonlocal theory of membrane elasticity,and（v）the relationship between the symmetry and the magnitude of the free energy.

Conductance and Capacity of Plain Lipid Membranes under Conditions of Variable Gravity

Biological cell membranes are complex structures containing mainly lipids and proteins. Functional aspects of such membranes are usually attributed to membrane integral proteins. However, it is well established that parameters of the lipid matrix are modifying the function of proteins. Additionally, electrical capacity and conductance of the plain lipid matrix of membranes are contributing directly to cellular functions as there is, for example, the propagation of action potentials. Accordingly the dependence of these parameters on changes of gravity might be important in the field of life sciences under space conditions. In this study consequently we have performed experiments in parabolic flight campaigns utilizing the patch-clamp technology to investigate conductance and capacity of plain lipid vesicle membranes under conditions of changing gravity. Both capacity and conductance were found to be gravity dependent. The changes in capacity could be contributed to changes in membrane geometry. Significant permeability in plain lipid membranes could be only observed at high potentials, where spontaneous current fluctuations occurred. The probability of these fluctuations was gravity dependent.

Mechanical responses of the bio-nano interface: A molecular dynamics study of graphene-coated lipid membrane

Bio-nano interfaces between biological materials and functional nanodevices are of vital importance in relevant energy and information exchange processes, which thus demand an in-depth understanding. One of the critical issues from the application viewpoint is the stability of the bio-nano hybrid under mechanical perturbations. In this work we explore mechanical responses of the interface between lipid bilayer and graphene under hydrostatic coating provides remarkable resistance to the pressure or indentation loads, We find that graphene loads, and the intercalated water layer offers additional protection. These findings are discussed based on molecular dynamics simulation results that elucidate the molecular level mechanisms, which provide a basis for the rational design of bionanotechnology- enabled aoolications such as biomedical devices and nanotheraoeutics.

Scaling Behaviors of Polymers on Lipid Membranes:Coupling of Polymer Chain Dynamics and Surface Thermal Fluctuations

Despite extensive researches on the motion of polymer chains on lipid membranes,the effect of membrane fluctuations on polymer chain dynamics remains poorly understood.Here we report single molecule tracking experiments that allow for comparable measurements of polymer chain diffusion dynamics on nanotubular and planar phospholipid membranes.We observe a super-diffusion behavior and no apparent chain-length-dependent mobility of polymer chains on nanotubular membranes,while a Brownian motion and apparent chain-lengthdependent mobility of polymer chains on planar membranes.We suggest the super-diffusion nature of polymer chains may be due to the thermal-fluctuations of lipid nanotubes,which can be described from a statistical thermodynamic phenomenon coupling of polymer chain dynamics and surface thermal fluctuations.We suggest that the existence of surface environment fluctuations should influence the dynamics of the adsorbed polymer chains.This study provides previously uncharacterized insights into polymer diffusion dynamics on thermal-fluctuating flexible surfaces,which is essential to understanding the effect of environment fluctuations on polymer chain behaviors.

Responses of Membrane Lipid Peroxidation and Endogenous Hormones of Soybean Seedlings to UV-B Radiation and Rare Earth

[ Objective] The aim was to provide strategies for development of rare earth and control of environmental pollution. [ Method] Responses of membrane lipid peroxidation and endogenous hormones of soybean seedlings to UV-B radiation and rare earth were studied through hydroponics in laboratory. [ Result] The results showed that under irradiation of UV-B（ T1-0.15 W/m^2 and T2-0.45 W/m^2）, chlorophyll and indole-3-acetic acid（IAA） contents firstly decreased during the stress phase （1 -5 d） and then increased during the restoration phase （6 -9 d） while contents of malonadialdehyde（MDA） and abscisic acid（ABA） gradually increased during the imposition of UV-B radiation （1 -5 d） and subsequently decreased during recovery from UV-B stress （6 -9 d） . With adding of La （III） with the concentration of 20 mg · L^-1 , the decline/dse trend of chlorophyll, IAA, MDA and ABA contents was slowed down during the stress period while the rise/decline speed was accelerated during the recovery period. [ Conclusion] It suggests that the regulation of La （ III ） on membrane lipid peroxidation and endogenous hormones could increase chlorophyll and IAA contents, improve the metabolism of reactive oxygen species （ ROS）, inhibit membrane lipid peroxidation, decrease the accumulation amount of ABA and alleviate injury of UV-B radiation to soybean seedlings. Further, the protective potential of La （ III ） was better under low UV-B radiation than under high one.

Photochemical Efficiency of PSⅡ and Membrane Lipid Peroxidation in Leaves of indica and japonica Rice (Oryza sativa) Under Chilling Temperature and Strong Light Stress Conditions

Relationships between fluorescence parameters and membrane lipid peroxidation in leaves of indica and japonica rice (Oryza sativa L.) during later growth stage were studied under chilling temperature and strong light stress conditions. Results showed that D1 protein contents of PSⅡ in photosynthetic apparatus dropped, the generation of antheraxanthin (A) and zeaxanthin (Z) of xanthophyll cycle were inhibited partly, PSⅡ photochemical efficiency (F v/F m)and non-photochemical quenching (q N) were also decreased obviously. In addition, endogenous active oxygen scavenger—superoxide dismutase (SOD) reduced, superoxide anion radical (O -· 2) and malondialdehyde (MDA) accumulated, as a result, photooxidation of leaves occurred under chilling temperature and strong light stress conditions. Obvious differences in the changes of the above mentioned physiological parameters between indica and japonica rice were observed. Experiments in leaves treated with inhibitors under chilling temperature and strong light conditions showed that indica rice was more sensitive to chilling temperature with strong light and subjected to photooxidation more than japonica rice. Notable positive correlation between D1 protein contents and F v/F m or (A+Z)/(A+Z+V), and a marked negative correlation between F v/F m and MDA contents were obtained by regression analysis in indica and japonica rice during chilling temperature and strong light conditions. According to the facts mentioned above, it was inferred that PSⅡ photochemical efficiency(F v/F m) was the key index to forecast for the prediction of photooxidation under stress circumstances and the physiological basis were the synthetic capacity of D1 protein and the protection of xanthophyll cycle.

Membrane Lipids and Their Fatty Acid Composition in Nostoc flagelliforme Cells

Nostoc flagelliforme Born. et Flah is highly adapted to drought stress, cold and light stresses, and suitable for growing in the unfavorable areas. This paper presents the results of the analysis of the membrane (mainly thylakoid membrane) lipids from N. flagelliforme in order to investigate the relationship between membrane lipid composition and stress resistance to this cyanobacteria. The membrane lipids are composed of monogalactosyl diacylglycerol (MGDG), digalactosyl diacylglycerol (DGDG), sulfoquinovosyl diacylglycerol (SQDG) and phosphatidylglycerol (PG). The major fatty acids in these lipids are palmitic (16∶0), palmitoleic (16∶1), stearic (18∶0), oleic (18∶1), linoleic (18∶2) and linolenic (18∶3) acids. In N. flagelliforme , polyunsaturated fatty acids account for 73% of the total fatty acids, much higher than that of the other cyanobacteria reported so far. Among which 16∶1 and 18∶3 are as high as 28.9% and 34.3% respectively. The high resistance of N. flagelliforme to abnormal conditions may be associated with the extent of unsaturation of fatty acids. In addition, the wild N. flagelliforme treated with water for 30 min and cultured for 24 h and the lipid and fatty acid composition were found to be not affected by water_absorption.

Effects of Exogenous Nitric Oxide on Membrane Lipid Peroxidation in Wheat Seeding Exposed to Enhanced Ultraviolet-B Radiation

[Objective] Effects of different concentrations of nitric oxide on membrane lipid peroxidation of wheat induced by enhanced UV-B radiation were researched,sodium nitroprusside （SNP） was selected as an exogenous nitric oxide（NO）donor.[Method] There are 3 groups including CK,UV treatment group （B）,B＋SNP treatment group,0,1,2,3,4 d sampling after treatment respectively,and physiological and biochemical indexes of MDA content and CAT,POD,SOD and so on were determined,repeated 3 times,and statistical analyzed.[Result] The results showed that,after the enhanced UV-B radiation,activity of the catalase （CAT）,superoxide dismutase （SOD） and of the guaiacol peroxidase （POD） all reduced apparently,and the concentration of malondialdehyde （MDA） increased obviously,leading to oxidative damage in wheat seedlings.Impose different concentrations of SNP after UV-B radiation,may mitigate oxidative damage of wheat seedling from different degrees,which was in agreement with the effect of making the concentration of MDA decrease and the activity of the CAT,SOD and POD all increased.The mitigation role of 0.01 mol/L SNP was more obvious for roots＇ oxidative damage,while 0.1 mmol/L SNP is more effective for oxidative damage of leaves.[Conclusion] Exogenous NO donor SNP had obvious relieve effects on oxidative damage of wheat seedlings caused by UV-B radiation,which can enhance adaptive capacity of plants to adversity stress.

Changes in Violaxanthin Deepoxidase Activity and Unsaturation of Thylakoid Membrane Lipids in Indica and Japonica Rice Under Chilling Condition and Strong Light

To explore the differences of sensitivities to chilling and strong light in indica and japonica rice (Oryza sativa L), the changes in unsaturation of thylakoid membrane lipids and xanthophyll cycle were studied under chilling condition and strong light. The contents of unsaturated fatty acids of thylakoid membrane lipids decreased and that of the saturated ones increased with the time of chilling and strong light treatment, resulting in the reduction of the index of unsaturation of fatty acids (IUFA). The activity of violaxanthin deepoxidase (VDE), a key enzyme of xanthophyll cycle, also reduced. The content of violaxanthin (V) increased, and the contents of antheraxanthin (A) and zeaxanthin M decreased, the ratio of (A+Z)/ (A+Z+V) decreased correspondingly. Arrhenius analysis showed that VDE was sensitive to both chilling and unsaturation level of thylakoid membrane lipids. Correlation analysis showed that there was distinctly positive relationships between IUFA of thylakoid membrane lipids and the activity of VDE, Fv/Fm, and D, protein content. Lower IUFA values, less fluidity and stability of thylakoid membrane lipids, lower VDE activity and (A+Z)/(A+Z+V) ratio were found in indica rice cv. Shanyou 63 than in japonica rice cv. 9516 under chilling and strong light.

Effects of Membrane Lipids on the Electron Transfer Activity of Cytochrome b_6f Complex from Spinach

A lipid_depleted cytochrome b 6f (Cyt b 6f) preparation was obtained from spinach (Spinacia oleracea L.) chloroplasts. Upon reconstitution of this preparation with the membrane lipids purified from spinach thylakoid, the effects of different membrane lipids on the electron transfer activity were studied. The results show that the electron transfer activity of Cyt b 6f is obviously stimulated to different extents, respectively, by monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), phosphatidylcholine (PC), phosphatidylglycerol (PG) and sulfoquinovosyldiacylglycerol (SQDG), and that the extents of stimulation may be closely related to the charge of the membrane lipids. The stimulation of non_charged lipids (MGDG, DGDG) and neutrally_charged lipid (PC) was high with a maximum enhancement of 89%, 75% and 77%, respectively; but the stimulation of two kinds of negatively_charged lipid (PG and SQDG) was relatively low with a maximum enhancement of 43% and 26%, respectively.

SERS imaging for label-free detection of the phospholipids distribution in hybrid lipid membrane

A label-free and low-cost mapping method based on SERS imaging was reported for illustrating the distribution of phospho- lipids with similar structures in binary lipid membranes on Ag nanoparticles （Ag NPs） films. The Ag NPs films exhibited strong SERS activity and good reproducibility which were investigated with p-aminothiopbenol （p-ATP） as probe molecules. Atomic force microscope （AFM） measurement proved that compact lipid membranes formed on the Ag NPs films. Basing on the Ag NPs films, the SERS spectra of phospholipids in the mixed lipid membranes were achieved and the inherent vibration of 1,2-dimyristoyl-sn-lycero-3-phosphoglycerol, sodium salt （DMPG）, 1482 cm-1, was used to distinguish between DMPG and dimyristoylphosphatidylcholine （DMPC）. The proportions of phospholipids in the mixed lipid membranes were represented by the intensity ratio of peaks at 1482 cm-1 and 1650 cm1 （R1482/1650） simultaneously： increasing R1482/1650 indicated higher propor- tion of DMPG and lower proportion of DMPC. SERS imaging of the lipid membranes was constructed as a combination of spacial information and the semiquantitative detection of phospholipids according to R1482/1650, which showed that the charged phospholipids, DMPG, aggregated in the hybrid lipid membranes. The presented mapping strategy based on SERS imaging carried out on Ag NPs films supplied a facile, label-free and inexpensive way for potential applications in the research on the structure of the lipid membrane, such as lipid domains and rafts.

Ion Channel Behavior of a Supported Bilayer Lipid Membrane Composed of 5,5-Ditetradecyl-2-(2-trimethyl-ammonioethyl)-1,3-dioxane Bromide Modified Glassy Carbon Electrode

A synthetic cationic surfactant, 5,5-ditetradecyl-2-(2-trimethyl-ammonioethyl)-1,3-dioxane bromide (DTDB), was used to construct a supported bilayer lipid membrane (s-BLM) coated on an underlying glassy carbon electrode (GCE). Electrochemical impedance spectroscopy (EIS), small-angle X-ray diffraction (SAXD) and cyclic voltammetry were used to characterize the s-BLM. Both EIS and SAXD data indicated that the synthetic lipid exists as a well-oriented bilayer in the membrane. The voltammetric study showed that the lipid membrane can open ion channels in the presence of C1O4- stimulant with Ru(bpy)32+ as marker ions and give distinct channel currents. The channels can be closed and open up again many times by removing or introducing ClO4- anions.

Study of the Ion Channel Behavior of Didodecyldimethylammonium Bromide Formed Bilayer Lipid Membrane Stimulated by PF_6^-

Bilayer lipid membranes (BLM) formed from didodecyldimethylammonium bromide were made on the freshly exposed surface of a glassy carbon (GC) and were demonstrated by the ac impedance spectroscopy. The ion channels of membrane properties induced by PF -_6 were studied by the cyclic voltammetric methods. Experimental results indicated that the ion channel of BLM was open in the presence of the PF -_6 due to the interaction of PF -_6 with the BLM, while it was switched off in the absence of PF -_6. Because the ion channel behavior was affected by the concentration of PF -_6, a sensor for PF -_6 can be developed.

Effects of salinity on activities of H^+-ATPase, H^+-PPase and membrane lipid composition in plasma membrane and tonoplast vesicles isolated from soybean(Glycine max L.) seedlings

The effects of NaCl stress on the H +-ATPase, H +-PPase activity and lipid composition of plasma membrane(PM) and tonoplast(TP) vesicles isolated from roots and leaves of two soybean cultivars(Glycine max L.) differing in salt tolerance(Wenfeng7, salt-tolerant; Union, salt-sensitive) were investigated. When Wenfeng7 was treated with 0.3%(W/V) NaCl for 3 d, the H +-ATPase activities in PM and TP from roots and leaves exhibited a reduction and an enhancement, respectively. The H +-PPase activity in TP from roots also increased. Similar effects were not observed in roots of Union. In addition, the increases of phospholipid content and ratios of phospholipid to galactolipid in PM and TP from roots and leaves of Wenfeng7 may also change membrane permeability and hence affect salt tolerance.

Effects of Vitamin E on the Activities of Protective Enzymes and Membrane Lipid Peroxidation in Leymus Chinensis under Drought Stress

Leymus chinensis seedlings were treated with 0.05--10 mmol/L vitamin E under osmotic stress in the presence of polyethylene glycol（PEG） as the stress reagent. The effects of the different concentrations of exogenous vitamin E on the activities of SOD, POD and free proline, and the MDA contents under drought stress were examined so as to ascertain the mechanism of Leymus chinensis resistance to drought stress and explore the possible preventive measures. The results indicate that the activities of SOD and POD decreased but the free proline and MDA contents increased as drought stress was accentuated, showing an enhancement of oxidative stress that may cause a decline in membrane stabilization. However, the activities of SOD and POD and the free proline content increased, whereas the MDA content reduced in Leymus chinensis pretreated with vitamin E in comparison with that of the control. This indicates that exogenous vitamin E enhanced the antioxidation of Leymus chinensis seedlings. It suggests that cytomembrane can be protected from damage by increasing the free proline content and the activities of SOD and POD that result in enhancing the drought resistance of Leymus chinensis seedlings.

Membrane Lipid Replacement: Clinical Studies Using a Natural Medicine Approach to Restoring Membrane Function and Improving Health

Functional oral supplements containing cell membrane glycerolphospholipids and antioxidants have been used to safely replace damaged membrane lipids that accumulate during aging and in various clinical conditions. This approach differs from other dietary and intravenous interventions in the composition of phospholipids and the presence of fructooligosaccharides that protect the phospholipids against oxidation and bile and enzymatic damage. Various chronic clinical conditions are characterized by membrane phospholipid oxidative damage, resulting in loss of cellular function. Recent clinical trials have shown the benefits of Membrane Lipid Replacement in replenishing damaged membrane lipids and restoring mitochondrial function, resulting in reductions in fatigue in aged subjects and patients with a variety of clinical diagnoses. Recent in vitro experiments with nonphysiological concentrations of phospholipids did not result in enhancement of mitochondrial electron transport enzyme activities. This can be explained by the use of the wrong phospholipid fatty acids, over-dilution of membrane constituents and mitochondrial swelling. A similar phenomenon was seen when human sperm were incubated in vitro with high concentrations of glycerolphospholipids and their motility was assessed. Only lower, more physiological concentrations of glycerolphospholipids stimulated sperm motility. Additional studies are needed to determine the functional effects of Membrane Lipid Replacement on other cellular membranes, such as the plasma membrane and other intracellular membranes of various cells and tissues.

Submergence induced changes of molecular species in membrane lipids in Arabidopsis thaliana

The composition of membrane lipids is sensitive to environmental stresses.Submergence is a type of stress often encountered by plants.However,how the molecular species of membrane lipids respond to submergence has not yet been characterised.In this study,we used a lipidomic approach to profile the molecular species of membrane lipids in whole plants of Arabidopsis thaliana that were completely submerged for three days.The plants survived one day of submergence,after which,we found that the total membrane lipids were only subtly decreased,showing significant decreases of monogalactosyldiacylglycerol(MGDG)and phosphatidylcholine(PC)and an increase of phosphatidic acid(PA);however,the basic lipid composition was retained.In contrast,three days of submergence caused plants to die,and the membranes deteriorated via the rapid loss of 96% of lipid content together with a 229% increase in PA.The turnover of molecular species from PG and MGDG to PA indicated that submergenceinduced lipid changes occurred through PA-mediated degradation.In addition,molecular species of extraplastidic PG degraded sooner than plastidic ones,lyso-phospholipids exhibited various patterns of change,and the double-bond index(DBI)remained unchanged until membrane deterioration.Our results revealed the unique changes of membrane lipids upon submergence and suggested that the major cause of the massive lipid degradation could be anoxia.

Effects of Low-Phosphorus Stress on Membrane Lipid Peroxidation and Protective Enzyme Activities in Leaves of Different Rice (Oryza sativa)Cultivars

Membrane lipid peroxidation and protective enzyme activity in leaves of low-phosphorus-tolerant rice cultivars Dalidao and Liantangzao 3, and low-phosphorus-sensitive cultivars Huzhanqi and Xinsanbaili were studied under low phosphorus stress with sandy culture. Results indicated that low-phosphorus stress aggravated the membrane lipid peroxidation in rice leaves, and it was more severe in low-phosphorus-sensitive cultivars than that in low-phosphorus-tolerant eultivars. During the period of low-phosphorus stress, the activities of SOD, CAT and POD maintained relatively stable in low-phosphorustolerant cultivars, whereas those increased obviously at early stage and subsequently decreased rapidly in the low-phosphorus-sensitive cultivars, suggesting that the absolute activities of protective enzymes had no relation with the low-phosphorus stress, while the changing trend was reverse.