Detection of motional heterogeneities in lipid bilayer membranes by dual probe fluorescence correlation spectroscopy

We report the detection of heterogeneities in the diffusion of lipid molecules for the three-component mixture dipalmitoyl-PC/dilauroyl-PC/cholesterol, a chemically simple lipid model for the mammalian plasma membrane outer leaflet. Two-color fluorescence correlation spectroscopy (FCS) was performed on giant unilamellar vesicles (GUVs) using fluorescent probes that have differential lipid phase partition behavior—DiO-C18:2 favors disordered fluid lipid phases, whereas DiI-C20:0 prefers spatially ordered lipid phases. Simultaneously-obtained fluorescence autocorrelation functions from the same excitation volume for each dye showed that, depending on the lipid composition of this ternary mixture, the two dyes exhibited different lateral mobilities in regions of the phase diagram with previously proposed submicroscopic two-phase coexistence. In one-phase regions, both dyes reported identical diffusion coefficients. Two-color FCS thus may be detecting local membrane heterogeneities at size scales below the optical resolution limit, either due to short-range order in a single phase or due to submicroscopic phase separation.     

Thermophysical properties of aqueous and frozen states of BSA/water/Tris systems

In the modelling and the optimization of pharmaceutical protein freeze–drying processes, thermophysical properties values of the formulation in frozen or in liquid states are necessary in order to determine the optimal operating conditions (temperature, pressure) of the two steps (sublimation, desorption) drying diagramme and the optimal storage conditions of the final freeze–dried product.

The most important thermophysical properties of BSA/water/Tris system buffered with Tris–HCl (5%, w/w) at pH 7, a standard formulation largely used in industrial freeze–drying process of pharmaceutical proteins, are reported in this paper. The state diagram of this formulation was determined by modulated temperature differential scanning calorimetry (MTDSC) and, then the vitreous transition temperatures were interpreted as a function of water content by the Gordon–Taylor equation. The same technique was used to experimentally determine the heat capacity of the BSA/water frozen system. Moreover, the transient hot wire probe method was used to measure the thermal conductivity of the frozen system as a function of temperature. It proved that the thermal conductivity and the apparent heat capacity values for this dilute formulation were reasonably close to the values for the pure water/ice system.

Sorption isotherms data were also measured by two different methods—the equilibrium with saturated salts solutions and also the controlled humidity oven. Water vapour sorption data were finally correlated by the three parameters Guggenheim, Anderson, De Boer (GAB) equation.     

A new interpretation of eutectic behavior for distearoylphosphatidylcholine-cholesterol binary bilayer membrane

We investigated the thermotropic phase behavior of the distearoylphosphatidylcholine (DSPC)–cholesterol binary bilayer membrane as a function of the cholesterol composition (X_ch) by fluorescence spectroscopy using 6-propionyl-2-(dimethylamino)naphthalene (Prodan) and differential scanning calorimetry (DSC). The fluorescence spectra, each of which has a single maximum, showed that the wavelength at the maximum intensity (λ_max) changed depending on the bilayer state: ca. 440 nm for the lamellar gel (L_β′ or L_β) and the liquid ordered (L_o) phases, ca. 470 nm for the ripple gel (P_β′) phase and ca. 490 nm for the liquid crystalline (L) phase, respectively. The transition temperatures were determined from the temperature dependences of the λ_max and endothermic peaks of the DSC thermograms. Both measurements showed that the pretransition disappears around X_ch = 0.035. The constructed temperature–X_ch phase diagram indicated that the phase behavior of the binary bilayer membrane at X_ch ≤ 0.15 is similar to that of general liquid–solid equilibrium for a binary system where both components are completely miscible in the liquid phase and completely immiscible in the solid phase. It was also revealed that the diagram has two characteristic points: a congruent melting point at X_ch = 0.08 and a peritectic-like point at X_ch = 0.15. The hexagonal lattice model was used for the interpretation of the phase behavior of the binary bilayer membrane. These characteristic compositions well correspond to the bilayer states in each of which cholesterol molecules are regularly distributed in the hexagonal lattice in a different way. That is, each composition of 0.035, 0.08 and 0.15 is nearly equal to that for the binary bilayer membrane which is entirely occupied with units, each composed of a cholesterol and 30 surrounding DSPC molecules within the next-next-next nearest neighbor sites (Unit (1:30): L_β(1:30)), with units, each of a cholesterol and 12 surrounding DSPC molecules within the next nearest sites (Unit (1:12): L_β(1:12)) or with units, each of a cholesterol and 6 surrounding DSPC molecules at the nearest neighbor sites (Unit (1:6): L_β(1:6)), respectively. Therefore, the eutectic behavior observed in the phase diagram was fully explainable in terms of a kind of phase separation between two different types of regions with different types of regular distributions of cholesterol. Further, the L_o phase was found in the higher X_ch-region (X_ch > 0.15). No endothermic peak over the temperature range from 10 to 80 °C at X_ch = 0.50 suggested that the single L_o phase can exist at X_ch > 0.50.     

Nutrient broth/PEG200/TritonX114/Tween80/Chloroform microemulsion as a reservoir of solubilized sitosterol for biotransformation to androstenedione

Microemulsions (ME) can act as a reservoir of solubilized hydrophobic substrates. The biotransformation of hydrophobic sitosterol to androstenedione (AD) with MEs prepared from nutrient broth and PEG 200 (1:1) as aqueous phase, 40 g/l sitosterol dissolved in chloroform as organic phase, Triton X114 and Tween 80 (1:1) as surfactant phase, was investigated. The phase behavior of this system was studied for ten different ratios(w/w), 10:0, 9:1, 8:2, 7:3, 6:4, 5:5, 4:6, 3:7, 2:8, 1:9 and 0:10 of the organic phase and surfactant at 30 °C. A pseudoternary phase diagram was constructed to demarcate the region giving stable MEs. The maximum solubility of sitosterol in ME medium was observed to be 8 g/l, which is 3 orders of magnitude higher than the reported sitosterol solubility of 2–4 mg/l in aqueous medium. The ME medium was used for biotransformation studies and a comparative result has been reported. Transmission electron microscopy of cells grown in ME having oil, surfactant and aqueous phase in the ratio of 6:14:80 showed a weakened cell wall structure that permitted production of 465.86 mg/l AD.     

Methods to investigate the structure and connectivity of the nervous system

Understanding the computations that take place in neural circuits requires identifying how neurons in those circuits are connected to one another. In addition, recent research indicates that aberrant neuronal wiring may be the cause of several neurodevelopmental disorders, further emphasizing the importance of identifying the wiring diagrams of brain circuits. To address this issue, several new approaches have been recently developed. In this review, we describe several methods that are currently available to investigate the structure and connectivity of the brain, and discuss their strengths and limitations.     

星座图聚类分析在小麦品种资源分类中的应用

根据星座图聚类分析的原理和方法,对濮阳市农科所从各地引进的20个小麦品种进行分析,分成3类,分析结果与田间表现相吻合。为育种者进行亲本选择和小麦品种资源分类提供了依据。     

氨基酸的分子结构与遗传密码简并及二维集合分类

根据氨基酸遗传密码子的简并程度,可将64个遗传密码子分为高简并度类（3,4,6度简并组）和低简并度类（1,2度简并组）两大类。高简并度类有9个氨基酸,其分子量比较小,等电点的分布比较集中。低简并度类有11个氨基酸,其分子结构比较复杂,参考Taylor对氨基酸特性的分类图,本文提出以分子量（M）及等电点（P）作为氨基酸的化学特性坐标,作出其二维集合MP分类图,MP分类图可以反映出氨基酸的各种属性,如分子量的大小,简并度的高低,极性与非极性、带电荷或不带电荷,疏水性与亲水性,以及氨基酸残基的种类等。根据氨基酸的分类分析,可以认为：高简并度氨基酸多数是脂烃类和羟脂烃类的氨基酸,分子量比较小,分子结构比较简单,大部分为疏子性,主要组成跨膜结构或蛋白质的结构域,可能是出现较早的氨基酸;而低简并度的氨基酸,分子结构比较复杂,分子量比较大,多数是和蛋白质功能有密切联系的基团,可能是进化出现较晚的结构。     

Equations for Obtaining Melting Points for the Ternary System Ethylene Glycol/Sodium Chloride/Water and Their Application to Cryopreservation

The present study describes the H(2)O-NaCl-ethylene glycol ternary system by using a differential scanning calorimeter to measure melting points (T(m)) of four different ratios (R) of ethylene glycol to NaCl and then devising equations to fit the experimental measurements. Ultimately an equation is derived which characterizes the liquidus surface above the eutectic for any R value in the system. This study focuses on ethylene glycol in part because of recent evidence indicating it may be less toxic to pancreatic islets than Me(2)SO, which is currently used routinely for islet cryopreservation. The resulting physical data and previously determined information regarding the osmotic characteristics of canine pancreatic islets are combined in a mathematical model to describe the volumetric response to equilibrium-rate freezing in varying initial concentrations of ethylene glycol.