Instability development in heated human erthrocytes.

Heated human erythrocytes gradually lose their form-maintaining structure as the temperature is increased to 50 degrees C and can behave in some respects as a viscous fluid. We have developed a technique for heating and stressing these cells that is novel, simple and quantitatively precise. We have applied this technique to heated human erythrocytes and have measured instability development in cells. We have employed instability growth theory to calculate a value for an effective surface tension which, in contrast to other methods of membrane surface tension measurement sought to minimize the effects of membrane supporting structural elements. The value obtained for the surface tension of the heated erythrocyte membrane was 0.9 . 10(-6) N/m with a range of variation from 0.4 . 10(-6)N/m to 1.4 . 10(-6) N/m. The methods described may be useful for determining fundamental physical parameters such as internal viscosity and interfacial tension in other systems.     

Physical and chemical properties of a biosurfactant synthesized by Rhodococcus species H13-A

The chemical and physical properties of a biosurfactant synthesized by hexadecane-grown Rhodococcus species H13-A are described. The biosurfactant is an anionic glycolipid consisting of 1 major and 10 minor components. The hydrophilic portion of the molecule is trehalose, which is acylated with normal C(10) to C(22) saturated and unsaturated fatty acids, C(35) to C(40) mycolic acids, hexanedioic and dodecanedioic acids, and 10-methyl hexadecanoic and 10-methyl octadecanoic acids. The major glycolipid species was identified as 2,3,4,6,2',3',4',6'-octaacyltrehalose, plus minor glycolipid species of di-, tetra- and hexa-acyltrehalose derivatives. The glycolipid exhibited a critical micelle concentration of 1.5?mg/mL and minimum interfacial tension value of 2?×?10(-2)?mN/m against decane, with a further reduction in interfacial tension to 6?×?10(-5)?mN/m in the presence of the cosurfactant pentanol. The phase behavior of the glycolipid indicates the formation of a surfactant-rich, "middle-phase" microemulsion containing liquid crystals, both of which are associated with surfactant systems having ultralow interfacial tension values. Key words: trehalose lipids, glycolipids, biosurfactants.     

一株产生脂肽的枯草芽孢杆菌的分离鉴定及脂肽对原油的作用

从大庆油田地层水中分离到一组能高效产生生物表面活性剂的菌株,采用sfp基因PCR鉴定的方法从中分离到一株芽孢杆菌ZW-3,该菌株能够产生大量表面活性物质,采用细菌生理生化鉴定结合16S rDNA序列的系统发育学分析确定该菌株为枯草芽孢杆菌(Bacillus subtilis),通过薄层层析色谱(TLC)、高效液相色谱(HPLC)分析其代谢产物,初步鉴定为脂肽(Lipopeptide);该脂肽生物表面活性剂理化性质显示它能使培养基的表面张力从68.92mN/m降低25.19mN/m、原油/水的界面张力从23.53mN/m降低到4.57mN/m,与1.8%的NaOH溶液复配可以将油水界面张力降低到1.2×10-3 mN/m,其临界胶束浓度为33.3mg/L(3.24×10-5 mol/L),并具有较好的乳化活性和发泡性能,说明该菌株代谢的脂肽生物表面活性剂在提高石油采收率中具有广泛的应用前景.     

Instability development in heated human erythrocytes

Heated human erythrocytes gradually lose their form-maintaining structure as the temperature is increased to 50°C and can behave in some respects as a viscous fluid. We have developed a technique for heating and stressing these cells that is novel, simple and quantitatively precise. We have applied this technique to heated human erythrocytes and have measured instability development in the cells. We have employed instability growth theory to calculate a value for an effective surface tension which, in contrast to other methods of membrane surface tension measurement sought to minimize the effects of membrane supporting structural elements. The value obtained for the surface tension of the heated erythrocyte membrane was 0.9 · 10^?6 N/m with a range of variation from 0.4 · 10^?6 N/m to 1.4 · 10^?6 N/m. The methods described may be useful for determining fundamental physical parameters such as internal viscosity and interfacial tension in other systems.     

Temperature dependence of blood surface tension

Whole blood surface tension of 15 healthy subjects recorded by the ring method was investigated in the temperature range from 20 to 40 degrees C. The surface tension omega as a function of temperature t ( degrees C) is described by an equation of linear regression as omega(t) = (-0.473 t + 70.105) x 10(-3) N/m. Blood serum surface tension in the range from 20 to 40 degrees C is described by linear regression equation omega(t) = (-0.368 t + 66.072) x 10(-3) N/m and linear regression function of blood sediment surface tension is omega(t) = (-0.423 t + 67.223) x10(-3) N/m.     

Scaling analysis of the concentration dependence on elasticity of agarose gel

Since the critical exponent of the elastic modulus is related to the spatial dimension and the critical exponent of the correlation length, depending on the characteristics of elasticity, we experimentally evaluated both the elastic modulus of a sol-gel transition system and also the correlation length. We could determine the correlation length of agarose gel by the dynamic light scattering method; it was well described by the power law as a function of the deviation from the sol-gel transition point. Three scaling laws between the critical exponent of the correlation length (v) and that of the elastic shear modulus (t) were compared, and the critical exponent of the elastic modulus was described by the equation of de Gennes expression (t=1+v(d-2), where d is the spatial dimension). This result suggests that agarose fibers are stiff enough to show scalar elasticity.     

Optimization and characterization of walnut beverage emulsions in relation to their composition and structure

A central composite rotatable design (CCRD) was used to evaluate the effects of walnut oil (WO, 3-6%, w/w) and gum arabic (GA, 5-10%, w/w) on the average droplet size (D(32)), specific surface area (SSA), polydispersity index (span), apparent viscosity, interfacial tension and opacity of walnut-beverage emulsions. The response surface methodology (RSM) showed that the significant second-order polynomial regression equations with high R(2) (>0.95) were successfully fitted for all responses as function of independent variables. The linear effect of WO had a significant term in all reduced models. The overall optimum region was found to be at the combined level of 10% (w/w) GA content and 5.84% (w/w) WO concentration. At this optimum point, D(32), SSA, span, apparent viscosity, interfacial tension and opacity of emulsions were 0.609 μm, 8.236 m(2)/ml, 0.886, 1.336 Pa s, 51.37 mN/m and 0.810, respectively. No significant (p>0.05) difference was found between the actual values and predicted values. Moreover, principal component analysis (PCA), conducted via PCA variable loadings and cluster dendrogram was able to discriminate the emulsions with different formulations into separate classes.     

Statistical analyses support power law distributions found in neuronal avalanches

The size distribution of neuronal avalanches in cortical networks has been reported to follow a power law distribution with exponent close to -1.5, which is a reflection of long-range spatial correlations in spontaneous neuronal activity. However, identifying power law scaling in empirical data can be difficult and sometimes controversial. In the present study, we tested the power law hypothesis for neuronal avalanches by using more stringent statistical analyses. In particular, we performed the following steps: (i) analysis of finite-size scaling to identify scale-free dynamics in neuronal avalanches, (ii) model parameter estimation to determine the specific exponent of the power law, and (iii) comparison of the power law to alternative model distributions. Consistent with critical state dynamics, avalanche size distributions exhibited robust scaling behavior in which the maximum avalanche size was limited only by the spatial extent of sampling ("finite size" effect). This scale-free dynamics suggests the power law as a model for the distribution of avalanche sizes. Using both the Kolmogorov-Smirnov statistic and a maximum likelihood approach, we found the slope to be close to -1.5, which is in line with previous reports. Finally, the power law model for neuronal avalanches was compared to the exponential and to various heavy-tail distributions based on the Kolmogorov-Smirnov distance and by using a log-likelihood ratio test. Both the power law distribution without and with exponential cut-off provided significantly better fits to the cluster size distributions in neuronal avalanches than the exponential, the lognormal and the gamma distribution. In summary, our findings strongly support the power law scaling in neuronal avalanches, providing further evidence for critical state dynamics in superficial layers of cortex.     

The interfacial tension of the lipid membrane formed from lipid-cholesterol and lipid-lipid systems

Interfacial tension has been determined for phosphatidylcholine-cholesterol, phosphatidylcholine-phosphatidylethanolamine, and phosphatidylethanolamine-cholesterol membranes. Phosphatidylcholine (PC), phosphatidylethanolamine (PE), and cholesterol (Ch) were to be investigated, because of their presence in biological membranes. Interfacial tension values of pure components are 0.81×10⁻³ N/m, 1.67×10⁻³ N/m, and 2.36×10⁻³ N/m, respectively. The 1∶1 complexes were formed during formation of the PC-Ch, PC-PE, and PE-Ch lipid membranes. The following parameters describing the complexes were determined: A ₃ ⁻¹ , the surface concentrations of the lipid membranes formed from these complexes; γ₃, the interfacial tensions of such membranes and K, the stability constants of these complexes.     

The mycocidal, membrane-active complex of Cryptococcus humicola is a new type of cellobiose lipid with detergent features.

The chemical composition of the mycocidal complex (formerly known as microcin) secreted by Cryptococcus humicola was investigated by chemical, mass spectrometric and nuclear magnetic resonance methods. The results indicate that the mycocidal complex is composed of glycolipids with a highly acetylated (up to five acetyl groups) cellobiose backbone [beta-D-Glcp-(1'-->4)-beta-D-Glcp] linked to the omega-hydroxyl group of alpha,omega-dihydroxy palmitate [16:0-alpha,omega-di-OH] with an unsubstituted carboxyl group. The acyl chain forming aglycon can be replaced by [18:0-(alpha,omega-di-OH)], [18:0-(alpha,omega-1,omega-tri-OH)], and [18:0-(alpha,omega-2,omega-tri-OH)]. The complex has a comparatively high surface activity; 0.5 mg/ml of it reduced the surface tension of 0.1 M NaHCO(3) from 71 mN/m to 37 mN/m and interfacial tension against n-hexadecane from 39 mN/m to 10 mN/m. The critical micelle concentration of the complex at pH 4.0, determined by the fluorometric method with N-phenyl-1-naphthylamine as fluorescent probe and by the De Nouy ring method, was 2 x 10(-5) M (taking the average molecular mass of the complex to be 750); it did not depend on the presence of 100 mM KCl and was an order of magnitude higher at pH 7.0. By fluorescence resonance energy transfer spectroscopy with N-(7-nitro-2,1,3-benzoxadiazol-4-yl)-phosphatidylethanolamine as energy donor and N-(rhodamine B sulfonyl)-phosphatidylethanolamine as energy acceptor the complex was shown to intercalate into the liposomal lipid matrix. Primary lesions caused by the complex in planar lipid bilayers were revealed as short-living current fluctuations of a broad spectrum of amplitudes. The mycocidal effect of the complex is suggested to be associated with its detergent-like properties.     

The ratio and allometric scaling of speed, power, and strength in elite male rugby union players

This study compared the effectiveness of ratio and allometric scaling for normalizing speed, power, and strength in elite male rugby union players. Thirty rugby players (body mass [BM] 107.1 ± 10.1 kg, body height [BH] 187.8 ± 7.1 cm) were assessed for sprinting speed, peak power during countermovement jumps and squat jumps, and horizontal jumping distance. One-repetition maximum strength was assessed during a bench press, chin-up, and back squat. Performance was normalized using ratio and allometric scaling (Y/X), where Y is the performance, X, the body size variable (i.e., BM or BH), and b is the power exponent. An exponent of 1.0 was used during ratio scaling. Allometric scaling was applied using proposed exponents and derived exponents for each data set. The BM and BH variables were significantly related, or close to, performance during the speed, power and/or strength tests (p < 0.001-0.066). Ratio scaling and allometric scaling using proposed exponents were effective in normalizing performance (i.e., no significant correlations) for some of these tests. Allometric scaling with derived exponents normalized performance across all the tests undertaken, thereby removing the confounding effects of BM and BH. In terms of practical applications, allometric scaling with derived exponents may be used to normalize performance between larger rugby forwards and smaller rugby backs, and could provide additional information on rugby players of similar body size. Ratio scaling may provide the best predictive measure of performance (i.e., strongest correlations).     

Dynamic interfacial properties of human apolipoproteins A-IV and B-17 at the air/water and oil/water interface

Viscoelastic behavior of proteins at interfaces is a critical determinant of their ability to stabilize emulsions. We therefore used air bubble surfactometry and drop volume tensiometry to examine the dynamic interfacial properties of two plasma apolipoproteins involved in chylomicron assembly: apolipoprotein A-IV and apolipoprotein B-17, a recombinant, truncated apolipoprotein B. At the air/water interface apolipoproteins A-IV and B-17 displayed wide area - tension loops with positive phase angles indicative of viscoelastic behavior, and suggesting that they undergo rate-dependent changes in surface conformation in response to changes in interfacial area. At the triolein/water interface apolipoprotein A-IV displayed maximal surface activity only at long interface ages, with an adsorption rate constant of 1.0 3 10(-)(3) sec(-)(1), whereas apolipoprotein B-17 lowered interfacial tension even at the shortest interface ages, with an adsorption rate constant of 9.3 3 10(-)(3) sec(-)(1). Apolipoprotein A-IV displayed an expanded conformation at the air/water interface and a biphasic compression isotherm, suggesting that its hydrophilic amphipathic helices move in and out of the interface in response to changes in surface pressure.We conclude that apolipoproteins A-IV and B-17 display a combination of interfacial activity and elasticity particularly suited to stabilizing the surface of expanding triglyceride-rich particles.     

植物代谢速率与个体生物量关系研究进展

植物的各项生理生态功能（例如,呼吸、生长和繁殖）都与个体生物量成异速生长关系。West, Brown及Enquist基于分形网络结构理论所提出的WBE模型认为：植物的代谢（呼吸）速率正比于个体生物量的3/4次幂。然而,恒定的“3/4异速生长指数”与实测数据、植物生理生态学等研究之间存在矛盾,引发激烈的争论。论文分析了不同回归方法对代谢指数的影响,重点对植物代谢速率与个体生物量异速生长关系研究进展进行了综述,分析并得出了植物代谢指数在小个体时接近1.0,并随着生物量的增加而系统减小,且其密切依赖于氮含量的调控的结论。据此,提出了进一步深入研究植物代谢速率个体生物量关系需要解决的一些科学问题。     

Analysis of adhesion of large vesicles to surfaces.

An experimental procedure that can be used to measure the interfacial free energy density for the adhesion of membranes of large vesicles to other surfaces is outlined and analyzed. The approach can be used for both large phospholipid bilayer vesicles and red blood cells when the membrane force resultants are dominated by isotropic tension. The large vesicle or red cell is aspirated by a micropipet with sufficient suction pressure to form a spherical segment outside the pipet. The vesicle is then brought into close proximity of the surface to be tested and, the suction pressure reduced to permit adhesion, and the new equilibrium configuration is established. The mechanical analysis of the equilibrium shape provides the interfacial free energy density for the surface affinity. With this approach, the measurable range of membrane surface affinity is 10(-4)-3 erg/cm2 for large phospholipid bilayer vesicles and 10(-2)-10 erg/cm2 for red blood cells.     

Critical exponents for sol–gel transition in aqueous alginate solutions induced by cupric cations

The sol–gel transition in aqueous alginate solutions of four alginate samples having different molecular weights (M_W) and M/G ratios induced by cupric cations was monitored by rheology measurements. The gel point f_gel and the relaxation critical exponent n were determined using the Winter’s criterion over the alginate concentration C_Alg of 1–4 wt%. The scaling for the zero shear viscosity η₀ before the gel point and the equilibrium modulus G_e after the gel point was established against the relative distance ε from the gel point at the concentration of C_Alg = 1 wt%, giving the critical exponents k and z. The results indicated that f_gel was almost independent of the alginate concentration and became higher for the sample with lower molecular weight. The critical exponent n decreased with the increase in C_Alg for these four Cu-alginate samples and the fractal dimension d_f estimated from n suggested a denser structure in the critical gel with high G content. The critical exponent n evaluated from k and z agreed well with n determined from the Winter’s criterion.     

Chemical and Physical Characterization of Interfacial-Active Lipids from Rhodococcus erythropolis Grown on n-Alkanes

Lipophilic compounds of the culture suspension containing Rhodococcus erythropolis DSM43215 had surfactant properties when the bacteria were cultivated with n-alkanes as the sole carbon source. Thirteen main components from a dichloromethane-methanol extract of the R. erythropolis cultures were isolated and characterized to specify quantitatively their surfactant properties, e.g., minimum surface and interfacial tensions and critical micelle concentrations. The interfacial activity of the organic extract was dominated by α,α-trehalose-6,6′-dicorynomycolates which reduced interfacial tension from 44 to 18 mN/m. Phosphatidylethanolamines which were also present in the organic extract reduced the interfacial tension below 1 mN/m. The trehalose corynomycolates had extremely low critical micelle concentrations in high-salinity solutions, and the interfacial properties were stabile in solutions with a wide range of pH and ionic strength.     

The interfacial properties of ApoA-I and an amphipathic alpha-helix consensus peptide of exchangeable apolipoproteins at the triolein/water interface

Apolipoprotein A-I (apoA-I) is the major protein in high density lipoprotein (HDL). During lipid metabolism, apoA-I moves among HDL and triacylglycerol-rich lipoproteins. The main structure and the major lipid binding motif of apoA-I is the amphipathic alpha-helix. To understand how apoA-I behaves at hydrophobic lipoprotein interfaces, the interfacial properties of apoA-I and an amphipathic alpha-helical consensus sequence peptide (CSP) were studied at the triolein/water (TO/W) interface. CSP ((PLAEELRARLRAQLEELRERLG)2-NH2) contains two 22-residue tandem repeat sequences that form amphipathic alpha-helices modeling the central part of apoA-I. ApoA-I or CSP added into the aqueous phase surrounding a triolein drop lowered the interfacial tension (gamma) of TO/W in a concentration- and time-dependent fashion. The gamma(TO/W) was lowered approximately 16 millinewtons (mN)/m by apoA-I at 1.4 x 10(-6) m and approximately 15 mN/m by CSP at 2.6 x 10(-6) m. At equilibrium gamma, both apoA-I and CSP desorbed from the interface when compressed and readsorbed when expanded. The maximum surface pressure CSP could withstand without being ejected (PiMAX) was 16 mN/m. The PiMAX) of apoA-I was only 14.8 mN/m, but re-adsorption kinetics suggested that only part of the apoA-I desorbed at Pi between 14.8 and 19 mN/m. However, above approximately 19 mN/m (PiOFF) the entire apoA-I molecule desorbed into the water. ApoA-I was more flexible at the TO/W interface than CSP and showed more elasticity at oscillation periods 4-128 s even at high compression, whereas CSP was elastic only at faster periods (4 and 8 s) and moderate compression. Flexibility and surface pressure-mediated desorption and re-adsorption of apoA-I probably provides lipoprotein stability during metabolic-remodeling reactions in plasma.     

The mycocidal, membrane-active complex of Cryptococcus humicola is a new type of cellobiose lipid with detergent features

The chemical composition of the mycocidal complex (formerly known as microcin) secreted by Cryptococcus humicola was investigated by chemical, mass spectrometric and nuclear magnetic resonance methods. The results indicate that the mycocidal complex is composed of glycolipids with a highly acetylated (up to five acetyl groups) cellobiose backbone [β-D-Glcp-(1′→4)-β-D-Glcp] linked to the ω-hydroxyl group of α,ω-dihydroxy palmitate [16:0-α,ω-di-OH] with an unsubstituted carboxyl group. The acyl chain forming aglycon can be replaced by [18:0-(α,ω-di-OH)], [18:0-(α,ω-1,ω-tri-OH)], and [18:0-(α,ω-2,ω-tri-OH)]. The complex has a comparatively high surface activity; 0.5 mg/ml of it reduced the surface tension of 0.1 M NaHCO₃ from 71 mN/m to 37 mN/m and interfacial tension against n-hexadecane from 39 mN/m to 10 mN/m. The critical micelle concentration of the complex at pH 4.0, determined by the fluorometric method with N-phenyl-1-naphthylamine as fluorescent probe and by the De Nouy ring method, was 2×10⁻⁵ M (taking the average molecular mass of the complex to be 750); it did not depend on the presence of 100 mM KCl and was an order of magnitude higher at pH 7.0. By fluorescence resonance energy transfer spectroscopy with N-(7-nitro-2,1,3-benzoxadiazol-4-yl)-phosphatidylethanolamine as energy donor and N-(rhodamine B sulfonyl)-phosphatidylethanolamine as energy acceptor the complex was shown to intercalate into the liposomal lipid matrix. Primary lesions caused by the complex in planar lipid bilayers were revealed as short-living current fluctuations of a broad spectrum of amplitudes. The mycocidal effect of the complex is suggested to be associated with its detergent-like properties.     

Line tensions, correlation lengths, and critical exponents in lipid membranes near critical points

Membranes containing a wide variety of ternary mixtures of high chain-melting temperature lipids, low chain-melting temperature lipids, and cholesterol undergo lateral phase separation into coexisting liquid phases at a miscibility transition. When membranes are prepared from a ternary lipid mixture at a critical composition, they pass through a miscibility critical point at the transition temperature. Since the critical temperature is typically on the order of room temperature, membranes provide an unusual opportunity in which to perform a quantitative study of biophysical systems that exhibit critical phenomena in the two-dimensional Ising universality class. As a critical point is approached from either high or low temperature, the scale of fluctuations in lipid composition, set by the correlation length, diverges. In addition, as a critical point is approached from low temperature, the line tension between coexisting phases decreases to zero. Here we quantitatively evaluate the temperature dependence of line tension between liquid domains and of fluctuation correlation lengths in lipid membranes to extract a critical exponent, ν. We obtain ν = 1.2 ± 0.2, consistent with the Ising model prediction ν = 1. We also evaluate the probability distributions of pixel intensities in fluorescence images of membranes. From the temperature dependence of these distributions above the critical temperature, we extract an independent critical exponent of β = 0.124 ± 0.03, which is consistent with the Ising prediction of β = 1/8.