NMR and optical activity observations on the helix-coil transition in poly(gamma-benzyl L-glutamate) solutions

The helix–coil transition of poly(γ-benzyl L -glutamate) was studied by comparing proton magnetic relaxation behavior with optical activity studies. The transition temperature as determined by magnetic relaxation was lower than that obtained by optical activity. The concentration dependence of the transition was also studied. The relationship of these experiments with previous NMR studies and also with calorimetric investigation of the transition is developed.     

The polymorphic phase behavior of dielaidoylphosphatidylethanolamine. Effect of n-alkanols

The polymorphic phase behavior of dielaidoylphosphatidylethanolamine (DEPE) has been investigated using spectrophotometry and 31P nuclear magnetic resonance (NMR). It has been demonstrated that the bilayer to inverted hexagonal phase transition can be observed by spectrophotometry. The effects of the methanol, ethanol, and propanol on both the gel to liquid crystal transition and the bilayer to inverted hexagonal transition were investigated by spectrophotometry. It was shown that these alcohols shift the gel to liquid-crystalline phase transition to lower temperature, whereas the bilayer to inverted hexagonal phase transition is shifted to higher temperatures by these alcohols. The structural transition between the bilayer and inverted hexagonal phase of pure DEPE was also investigated by 31P-NMR.     

Forest Transition in Xishuangbanna,Yunnan

Forest transition is a process of overall forest cover from net loss to net gain over time. Forest transition especially the process after turning point from deforestation to reforestation has inspired lots of researches for its potential to improve environmental services. China has undergone forest transition since the 1980s. However, in tropical China, deforestation was still existed, while the overall forest cover increased greatly. To investigate this issue, we conducted this research by classifying overall forest into natural forest and plantation in Xishuangbanna, which has undergone forest transition and deforestation and overall forest cover increasing. We found that natural forest continues decreasing while overall forest cover increasing and plantation expansion in forest transition. The forest transition in Xishuangbanna was found to be a tree cover transition, which was mainly contributed by large plantation expansion. In Xishuangbanna, deforestation is still undergoing after its overall forest cover transition occurred in 1988. The general overall forest definition used by forest transition will not be able to recognize deforestation when natural forests are displaced by plantations because the overall forest cover remains unchanged or even increasing. We therefore recommended to classify forest types in forest transition researches.     

A high melting (105 degrees C) form of chromatin characterizes the potential of cells for mitosis

The nuclei from different types of dividing cultured cells melted as four thermal transitions: I (60 degrees C), II (76 degrees C), III (88 degrees C), and IV (105 degrees C). The fourth transition was the predominant endotherm in all types of cells examined. In the melting profile of nuclei obtained from nondividing density-inhibited fibroblasts, transition IV remained the major endotherm; however, it was lost in nuclei from differentiated myoblasts and nutrient-depleted cells. In these cells, the loss in transition IV was compensated by a concomitant increase in transition III. In the nutrient-deprived cells the decrease in transition IV was followed by a gradual lowering in its melting temperature. The complete loss of transition IV was correlated with loss of cellular capacity to divide.     

Sterol-phospholipid interactions in model membranes. Effect of polar group substitutions in the cholesterol side-chain at C20 and C22

The interactions of phospholipids with four different cholesterol derivatives substituted with one OH or one keto group at position C20 or C22 of the side-chain were studied. The derivatives were the 22,R-hydroxy; 22,S-hydroxy; 22-keto- and 20,S-hydroxycholesterol. Two aspects of the interactions were investigated: (1) the effect of the cholesterol derivatives on the gel leads to liquid crystalline phase transition of dipalmitoylphosphatidylcholine (DPPC) and of dielaidoylphosphatidylethanolamine (DEPE) monitored by differential scanning calorimetry and (2) The effect on the lamellar leads to hexagonal HII phase transition of DEPE monitored by DSC and by 31P-NMR to determine structural changes. The gel leads to liquid crystalline phase transition was affected by the cholesterol derivatives to a much larger extent in the case of DPPC than of DEPE. In both cases, there was a differential effect of the four derivatives, the 22,R-hydroxycholesterol being the less effective. In DPPC-sterol 1:1 systems, 22,R-hydroxycholesterol does not suppress the melting transition, the delta H values becomes 7.1 kcal X mol-1 as compared to 8.2 kcal X mol-1 for the pure lipid. 22,S-OH cholesterol has a much stronger effect (delta H = 3.1 kcal X mol-1) and 22-ketocholesterol suppresses the transition completely. In DEPE mixtures of all these compounds, the melting transition of the phospholipid is still observable. The transition temperature was shifted to lower values (-13.5 degrees C in the presence of 20,S-OH cholesterol). The delta H of the transition was lowered by these compounds except in DEPE-22,R-OH cholesterol mixtures and the cooperativity of the transition (reflected by the width at half peak height) was reduced. The lamellar leads to hexagonal HII phase transition was also affected by the presence of these cholesterol derivatives. The transition temperature value was depressed with all these compounds. 20,S-OH cholesterol was the most effective followed by 22,R-OH cholesterol. The delta H of the transition was not strongly affected. The molecular interfacial properties of these derivatives were studied by the monomolecular film technique. It is most likely that 22,R-OH cholesterol due to the hydroxyl groups at the 3 beta- and 22,R-positions orients with the sterol nucleus lying flat at the air/water interface, since the compression isotherm of either the pure sterol or the DOPC-sterol mixture (molar ratio, 1:1) monomolecular film exhibits a transition at approx. 103 A2.(ABSTRACT TRUNCATED AT 400 WORDS)     

PHP14通过与Vimentin相互作用影响TGF-β诱导的肝细胞AML-12上皮-间质转化

目的:探讨PHP14在上皮-间质转化中的作用及其可能作用机制。方法:建立了研究上皮-间质转化的细胞模型小鼠肝细胞AML-12。在AML-12中过表达PHP14,通过光学显微镜进行形态学观察,应用实时荧光定量PCR和蛋白质印迹检测AML-12上皮-间质转化中相关标志物的表达情况。通过免疫共沉淀检测PHP14与Vimentin的相互作用情况。结果:小鼠肝细胞AML-12可作为研究上皮-间质转化的较好细胞模型。在AML-12中过表达PHP14可促进AML-12细胞的上皮-间质转化,并增强其运动能力。过表达PHP14可上调Vimentin的蛋白质水平,而对其他上皮-间质转化相关标志物表达没有影响。进一步的研究发现,PHP14可与Vimentin相互作用。结论:PHP14通过与Vimentin相互作用,稳定Vimentin的蛋白质水平,从而参与并调节上皮-间质转化。     

Interaction of surfactants with vesicle membrane of dipalmitoylphosphatidylcholine. Effect on gel-to-liquid-crystalline phase transition of lipid bilayer

The gel-to-liquid-crystalline phase transition of dipalmitoylphosphatidylcholine (DPPC) vesicle membrane was observed in the presence of various types of surfactants; sodium alkylsulfates, alkyltrimethylammonium bromides, alkanoyl-N-methylglucamides, and hexaethyleneglycol mono n-dodecyl ether. The phase transition was monitored by a change in scattered light intensity of the lipid suspension. For all the surfactants examined, the phase transition temperature was depressed linearly with the surfactant concentration in the measured concentration range, from which the partition coefficient, K, of the surfactant between bulk solution and lipid membrane was estimated. Except alkyltrimethylammonium bromides, log K and log CMC showed a linear relationship, which indicates that the driving force to transfer the surfactant from bulk solution to lipid membrane is a hydrophobic interaction. The addition of surfactants increased the transition width. The extent of widening the transition width was in the order of sodium alkylsulfate greater than alkyltrimethylammonium bromides greater than hexaethyleneglycol mono n-dodecyl ether; in the case of alkanoyl-N-methylglucamides, the transition width was not affected by the addition. These effects on the transition width was interpreted qualitatively in terms of the cooperativity of the transition.     

Sol-gel transition temperature of PLGA-g-PEG aqueous solutions

Aqueous solutions of poly(DL-lactic acid-co-glycolic acid)-g-poly(ethylene glycol) copolymers exhibited sol-to-gel transition with increasing temperature. Further increase in temperature makes the system flow and form a sol phase again. Subcutaneous injection of a copolymer aqueous solution (0.5 mL) resulted in a formation of a hydrogel depot by temperature-sensitive sol-to-gel transition in a rat model. The reliable determination and control of sol-to-gel transition temperatures are the most important issues for this kind of sol-gel reversible hydrogel. The sol-to-gel transition temperature determined by the test tube inverting method, falling ball method, and dynamic mechanical analysis coincided within 1-2 degrees C. Fine tuning of the sol-to-gel transition temperature was achieved by varying the ionic strength of the polymer solutions and by mixing two polymer aqueous solutions with different sol-to-gel transition temperatures. The sol-to-gel transition temperature of polymer mixture aqueous solutions was well described by an empirical equation of miscible blends, indicating miscibility of the two polymer systems in water on the molecular level.     

云南西双版纳地区森林转型特征(英文)

森林转型是指森林覆盖率由净减少到净增加的过程。中国森林早在20世纪80年代就进入了转型期,然而,中国热带地区的总森林覆盖率虽呈增长趋势,但依旧存在着天然林大量被毁的现象。鉴于天然林对森林生态系统功能的重要作用,本研究通过加入森林类型分类的内容,以西双版纳为例探讨其森林转型的真实特征。结果表明:森林转型理论单纯以"总森林"覆盖率为研究对象,忽视了其他森林类型的动态变化,甚至掩盖了"天然林"的真实动态变化。西双版纳的森林转型主要是人工种植林的扩张所致,只是树木数量统计上的转型。事实上,自1988年以来,西双版纳的天然林一直在锐减。所以建议未来关于森林转型的研究应将"森林"区分成不同的森林类型加以研究。     

Phase transition kinetics of phosphatidic acid bilayers A stopped-flow study of the electrostatically induced transition

The kinetics of the electrostatically induced phase transition of dimyristoyl phosphatidic acid bilayers was followed using the stopped-flow technique. The phase transition was triggered by a fast change in the pH or the magnesium ion concentration and followed by recording the time dependence of the absorbance. When the phase transition was induced by a pH jump the time course of the absorbance could be described by two exponentials, their time constants displaying the for cooperative processes characteristic maximum at the transition midpoint. The time constants are in the 10 and 100 ms range for the H⁺ triggered transition from the fluid to the ordered state. A third slower process shows no appreciable temperature dependence and is probably caused by vesicle aggregation. For the OH^--induced transition fron the ordered to the fluid state the time constants are in the 100 and 1000 ms range. The fluid-ordered transition could also be triggered by addition of magnesium ions. Of the several observed processes only the fastest in the 10–100 ms time range could definitely be assigned to the fluid-ordered transition while the others are due to aggregation phenomena. The experimental data were compared with results obtained from pressure jump experiments and could be interpreted on the basis of theories for non-equilibrium relaxation.     

The effect of head group structure on phase transition of phospholipid membranes as determined by differential scanning calorimetry

The phase transition characteristics of cardiolipin and phosphatidylglycerol suspensions were investigated by differential scanning calorimetry. The phase transition temperatures for dimyristoylphosphatidylglycerol, tetramyristoylcardiolipin, dipalmitoylphosphatidylglycerol and tetrapalmitoylcardiolipin were 25.0, 47.0, 40.5 and 62.2 degrees C, respectively. The phase transition temperature for a mixture of two analogous phospholipids was higher than that for phosphatidylglycerol alone, but lower than that for cardiolipin alone. It increased along with cardiolipin content. The phase transition temperature for cardiolipin was increased in the presence of divalent cations, particularly Ca2+. The results indicate that the head group of cardiolipin by itself can increase the phase transition temperature.     

Phase transitions of the purple membranes of Halobacterium halobium

Purple membranes of Halobacterium halobium were studied by differential scanning calorimetry. No transition was detected at temperatures below 70 degrees C. A small endothermic transition was seen at about 80 degrees C and a larger one at 100 degrees C. The larger transition is the irreversible denaturation of bacteriorhodopsin. The smaller transition is accompanied by a change in the visible absorption spectrum and is believed to be reversible, involving a cooperative change in crystalline structure of the membrane.     

Calorimetric studies of the thermal denaturation of cytochrome c peroxidase

Two endotherms are observed by differential scanning calorimetry during the thermal denaturation of cytochrome c peroxidase at pH 7.0. The transition midpoint temperatures (tm) were 43.9 +/- 1.4 and 63.3 +/- 1.6 degrees C, independent of concentration. The two endotherms were observed at all pH values between 4 and 8, with the transition temperatures varying with pH. Precipitation was observed between pH 4 and 6, and only qualitative data are presented for this region. The thermal unfolding of cytochrome c peroxidase was sensitive to the presence and ligation state of the heme. Only a single endotherm was observed for the unfolding of the apoprotein, and this transition was similar to the high-temperature transition in the holoenzyme. Addition of KCN to the holoenzyme increases the midpoint of the high-temperature transition whereas the low-temperature transition was increased upon addition of KF. Binding of the natural substrate ferricytochrome c to the enzyme increases the low-temperature transition by 4.8 +/- 1.3 degrees C but has no effect on the high-temperature transition at pH 7. The presence of cytochrome c peroxidase decreases the stability of cytochrome c, and both proteins appear to unfold simultaneously. The results are discussed in terms of the two domains evident in the X-ray crystallographic structure of cytochrome c peroxidase.     

Relationship between configuration, function, and permeability in calcium-treated mitochondria.

Low levels of calcium (100 nmol/mg) added to beef heart mitochondria induced a configurational transition from the aggregated to the orthodox state and a simultaneous uncoupling of oxidative phosphorylation. The primary effect of calcium was to cause a nonspecific increase in the permeability of the inner membrane, resulting in entry of sucrose into the matrix space and the observed configurational transition. The uncoupling and permeability change induced by calcium could readily be reversed by lowering the calcium:magnesium ratio in the presence of either substrate or ATP. The configurational state, however, remained orthodox. This, along with studies of hypotonically induced orthodox mitochondria in which the membrane remained coupled and impermeable until after the addition of calcium, led to the conclusion that coupling was related to the permeability state of the inner membrane rather than the configurational state. Phosphate, arsenate, or oleic acid was found to cause a transition similar to that induced by calcium. Studies with the specific calcium transport inhibitors, EGTA, ruthenium red, and lanthanum revealed that endogenous calcium is required for the anion-induced transitions. A single mechanism was further indicated by a common sensitivity to N-ethylmaleimide. Strontium was ineffective as an inducer of the transition, even though it is transported by the same mechanism as calcium. This indicates that there are additional calcium-binding sites responsible for triggering the transition. Magnesium and calcium appeared to compete for these additional sites, since magnesium competitively inhibited the calcium-induced transition, but had no effect on calcium uptake. Calcium was found to potently inhibit the respiration of all NAD+-requiring substrates prior to the transition. Strontium also produced this inhibition without a subsequent transition. ATPase activity was induced at the exact time of transition with calcium and was not induced by strontium. This suggests that calcium-induced ATPase uniquely required the transition for activity, in contrast to the ATPase induced by uncoupler or valinomycin. The results of this work indicate that mitochondria have a built-in mechanism which responds to low levels of calcium, phosphate, and fatty acids, resulting in simultaneous changes, including increased permeability, inducation of ATPase, uncoupling of oxidative phosphorylation, and loss of respiratory control.     

Thermotropic behavior of dipalmitoylphosphatidylcholine vesicles reconstituted with the glycoprotein of vesicular stomatitis virus

The vesicular stomatitis virus glycoprotein reconstituted into dipalmitoylphosphatidylcholine (DPPC) vesicles exerts a profound effect upon the DPPC gel to liquid-crystalline phase transition. The glycoprotein was reconstituted into DPPC vesicles by octyl glucoside dialysis. The gel to liquid-crystalline phase transition of these vesicles was monitored by differential scanning calorimetry. Vesicles formed in the absence of glycoprotein (600--2100-A diameter) underwent the phase transition at 41.0 degrees C and had an associated enthalpy change of 8.0 +/- 1.6 kcal/mol. Increasing the mole ratio of glycoprotein to DPPC in the vesicles to 0.15 mol % reduced both the transition temperature and the transition enthalpy change. The enthalpy change as a function of the mole percent glycoprotein could be fit to a straight line by a least-squares procedure. Extrapolation of the results to the glycoprotein concentration where the enthalpy change was zero indicated one glycoprotein molecule bound 270 +/- 150 molecules of DPPC.     

Membrane lipid composition and the interaction of pardaxin: the role of cholesterol

Modulation by pardaxin of the phase transitions of dimyristoyl phosphatidylcholine, 1-stearoyl-2-oleoyl phosphatidylcholine or 1-stearoyl-2-oleoyl phosphatidylglycerol in the presence or absence of cholesterol was studied by differential scanning calorimetry. The transition enthalpy of each of the phospholipids was lowered by pardaxin and there was a small decrease in the transition temperature. Addition of cholesterol and pardaxin to dimyristoyl phosphatidylcholine resulted in a very marked lowering of the transition temperature. Although the peptide broadens the transition of the pure phospholipids, it sharpens the transition of mixtures of the phospholipids with cholesterol. This and the observation that pardaxin also causes the formation of crystallites of anhydrous cholesterol, suggest that the peptide promotes redistribution of cholesterol in the membrane.     

A differential scanning calorimetric study of the conformational transitions of schizophyllan in mixtures of water and dimethylsulfoxide

The thermal conformational transitions of two sonicated samples of schizophyllan were studied in water-dimethylsulfoxide (DMSO) mixtures by high-sensitivity differential scanning calorimetry (DSC). Two transitions were observed over most of the range of solvent compositions. These were assigned to an internal change of the triple helix [T. Itou et al. (1986) Macromolecules 19, 1234-1240] and a triple-helix-single-coil transition [T. Sato et al. (1981) Carbohydr. Res. 95, 195-204], respectively. In water, the former transition observed at lower temperature for a low molecular weight sample, U-1, is centered at 3 degrees C and characterized by the specific enthalpy, delta hcal = 3.29 J g-1. A higher molecular weight sample, M-2, showed this transition at 7 degrees C with delta hcal = 4.39 J g-1. The transition temperature for both samples increased with increasing DMSO concentration up to about 50 degrees C at 70 weight % DMSO, and then rapidly decreased with increasing DMSO concentration, with about 3 degrees C higher for M-2 than for U-1 over the DMSO concentration. The transition was not observed when the concentration of DMSO exceeded 87%. It was found that delta hcal for both samples was a linear function of t 1/2, the temperature of half-completion in degrees C, delta hcal = 0.177t + 2.96. The triple helix-coil transition was observed at around 127 degrees C for U-1 and above 130 degrees C for M-2 in the range of DMSO composition below about 70%. The transition temperature decreased with increasing DMSO concentration at above 70%, and the transition finally disappeared when the DMSO concentration exceeded 90%. The plot of delta hcal vs. t 1/2 for the transition of both samples gave a linear relation, delta hcal = 0.253t - 10.58. The reversibility of the transition at lower temperature was demonstrated by the reversibility of the curves when the first heating was stopped before the second transition. Once the heating was performed over the second transition, the reheating DSC curves showed several endothermic peaks, indicating the irreversibility of the transition and heterogeneity in the conformation of the heated schizophyllan.     

Kinetics and dynamics for light state transition in cyanobacterium Spirulina platensis cells

Light state transition in oxygenic organisms was defined as the ability to equalize the excitation of the two photosystems for maximal photosynthetic efficiency. In cyanobacteria, extensive researches on state transition have continuously provided new knowledge in the past decades but the molecular mechanism and physiological significance are still ambiguous. In this work, kinetics and dynamics of the transition from state 1 to state 2 in cyanobacterium Spirulina platensis cells were studied at different intensity of orange light from 10 to 120 μmol m(-2) s(-1). It was revealed that the state transition worked constantly independent of light intensity while the rates varied. The synchronous fluorescence kinetics for phycobilisome (PBS) and photosystem components indicated that the state transition was entirely regulated by "mobile PBS", and continuously changed fluorescence amplitudes suggested a series of intermediate states were involved between state 1 and state 2. The dynamic property of PBS movement during the state transition was revealed by (1,0) distribution of photo-linkable PBSs, indicating a collective movement of all PBSs. The results suggest that state transition in cyanobacteria possesses not only physiological but also photochemical significance.     

The influence of dioxan on the bilayer and monolayer phase transition of phospholipids

The influence of 1.4.-dioxan on the bilayer phase transition of various phospholipids was studied by differential scanning calorimetry and turbidity measurements. The addition of 1.4.-dioxan to lipid bilayers decreases the transition temperature T_m increases the transition enthalpy of the transition. The cooperativity of the transition is unaffected. The phospholipid monolayer transition from the liquid-condensed to the liquid-expanded phase was measured by recording area versus temperature curves at constant surface pressure (isobars). The monolayer transition temperature at constant surface pressure is increased when 1.4.-dioxan is added to the subphase. The change in molecular area becomes larger. A comparison of monolayer isobars on water and water/dioxan as subphase at constant surface tension rather than surface pressure leads to a decrease of the transition temperature on water/dioxan as subphase. This decrease as well as the larger change in molecular area at the monolayer transition can be correlated to the decrease in T_m and the increase in the transition enthalpy of the corresponding bilayer system. 1.4.-Dioxan seems to accumulate at the lipid head group/water interface, thus lowering the tension of the bilayer membrane. This cyclic ether can be used for altering the characteristics of bilayer membranes without disturbing the lipid chain organization.     

The mechanism of helical transition of proteins by organic solvents

This paper describes a theory for the mechanism of three-state transition of proteins which is often observed in aqueous organic cosolvent systems, i.e., from the native, via intermediate to helical forms. The first transition, accompanied by changes in the tertiary and/or secondary structures, was explained by larger bindings of the organic solvent molecules to the intermediate than to the native state; the second transition, resulting in changes mainly in the secondary structure, i.e., helical transition, was explained by less hydration sites for the helical state. Computer simulations of the transition were carried out using plausible values for the number of alcohol and water binding sites of proteins as well as for the equilibrium constant of the transitions in the absence of cosolvent. A reasonable agreement with the experimental transitions was observed. The stronger effect of alcohols with longer alkyl chains was explained by their greater binding to nonpolar groups and their larger exclusion from peptide groups.