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PubMed2006

Structural and dynamical examination of the low-temperature glass transition in serum albumin.

The nuclear magnetic transverse decay and the proton second moment of bovine serum albumin samples dry and hydrated with different water isotope compositions show that at temperatures around 170 K, there is a dramatic change in the dynamics of the water associated with the protein interface. By comparison, observation of the protein protons when hydrated with deuterium oxide provides no evidence for significant dynamical changes near 170 K. The proton second moment of the hydrated protein shows that the protein structure becomes more open with increasing hydration from the lyophilized condition and that the side chains extend from the protein surface into the solvent in the hydrated but not the dry cases. The proton second moment of serum albumin hydrated with H(2)O increases dramatically with decreasing temperature near 170 K, demonstrating that the water forms a rigid solid around the protein which effectively fills the surface irregularities created by the protein fold. Solvation with dimethyl sulfoxide yields small effects compared with water.

Computer Simulation↗

PubMed1989

Kinetics and in vitro origin of the temperature-dependent transition of the estrogen receptor monomer.

Partitioning of estrogen receptors in aqueous two-phase polymer systems has provided the basis for a detailed kinetic analysis of the effects of temperature on estrogen receptor (ER) structure in vitro. Exposure to temperatures of 0-30 degrees C increased the rate of change in ER partition coefficients by up to 100-fold but did not affect the final extent of the process. The temperature-dependent change in ER partition coefficients was characterized by a linear Arrhenius plot and an activation energy of 25 kcal/mol. The rate of the temperature-dependent ER transition (28 degrees C) was found to be unaffected by greater than 50-fold changes in receptor concentration, which indicates that the temperature-dependent change in partition coefficients reflects a first-order process. The partition coefficients of heated ER were unaffected by subsequent 18-h incubations at 0 degree C, indicating that the temperature-dependent ER transition is irreversible in vitro. Direct heating of the unoccupied ER resulted in both a change in ER partition coefficients and a loss of ER binding sites. The temperature-dependent change in unoccupied ER partition coefficients was complete within 30 min at 28 degrees C and yielded a first-order rate constant that was the same as that obtained for heating the receptor-estradiol complex at 28 degrees C. In contrast, the loss of unoccupied ER binding sites that occurred during 28 degrees C incubations did not reach completion after 150 min of heating and was found to behave as a second-order process.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2000

Binding study of riboflavin-binding protein with riboflavin and its analogues by differential scanning calorimetry.

Thermal unfolding parameters of hens' egg-white riboflavin-binding-protein (RBP) were measured by differential scanning calorimetry. Thermal denaturation scans of apoRBP and RBP complexes with riboflavin and its analogues (FMN, N10 DL-glyceryl isoalloxazine, and N10 omega-hydroxypentyl isoalloxazine) have been measured. It was found that ligand binding causes increase of RBP thermal stability, as manifested by a change of denaturation temperature from 60.8 degrees C for apoRBP to 72.8 degrees C for RBP-Rf complex. For RBP-FMN complex, the denaturation temperature of 73.0 degrees C was even higher than for the RBP-Rf complex. The other two flavin analogues showed transition temperatures in between 66.9 degrees C and 68.8 degrees C, respectively. Analysis of excess heat capacity data showed that the best fit was the sum of two independent thermal transitions. One of the transitions, which contributed approximately 70% to the total heat effect, has transition temperature in the broad range of 60.5-73.2 degrees C; the other transition temperature is in the narrower range of 65.4-71.1 degrees C. The observed transitions can be related to RBP domains.

Calorimetry, Differential Scanning↗

PubMed1980

Similar effect of proteolipid apoproteins from human myelin (lipophilin) and bovine white matter on the lipid phase transition.

The proteolipid apoprotein from bovine white matter has been reported to increase the phase transition temperature of dimyristoyl phosphatidylcholine, in contrast to a proteolipid apoprotein fraction from human myelin, called lipophilin, which decreases the enthalpy without altering the phase transition temperature. Since these results lead to different conclusions concerning the structure and amount of boundary lipid surrounding these proteins, the effects of the two proteins on the phase transition of dimyristoyl phosphatidylcholine were compared. Neither protein has any effect on the phase transition temperature, regardless of the method of delipidation of the protein, the amount of residual lipid, the method of incorporation into vesicles, or heating rates used for differential scanning calorimetry. However, a higher melting component was observed when decomposition of the lipid to lysophosphatidylcholine had occurred. Addition of as little as 6% of the decomposition products of dimyristoyl phosphatidylcholine, lysodimyristoyl phosphatidylcholine and myristic acid, is enough to produce a higher-temperature peak. The intensity of this peak increases with increasing protein concentration similar to the reported result on the bovine white matter proteolipid. The question as to whether the protein-induced decrease in enthalpy is due to boundary lipid or entrapment of lipid in protein aggregates was also addressed by studying the appearance of the intramembranous protein particles by freeze-fracture electron microscopy at temperatures above and below the phase transition and between the premelt and main transitions. The protein is randomly dispersed above the phase transition. At low concentrations, below the phase transition, it clusters, forming particle-free and particle-rich areas, but does not aggregate. At higher concentrations it is randomly dispersed below the premelt and main transition but is clustered between the premelt and main transition. Since the protein is more randomly dispersed above the transition than below, the reduction in enthalpy of the freezing transition was compared to that of the melting transition and was found to be identical, suggesting that the withdrawal of lipid from the phase transition is probably not due to lipid entrapment but due to the formation of a boundary lipid interface between the protein and the bulk lipid.

Animals↗

PubMed1981

Influence of growth hormone and thyroxine on thermotropic effects of respiration and 1-anilino-8-naphthalene sulfonate fluorescence and on lipid composition of cardiac membranes.

The effects of hypophysectomy and subsequent administration of growth hormone and/or L-thyroxine on thermotropic properties of State 3 respiration (ADP-induced), cholesterol, phospholipid and fatty acid composition of phospholipid fraction were examined in myocardial mitochondria of rats. Temperature-dependence of 1-anilino-8-naphthalene sulfonate fluorescence was determined in vesicles prepared from lipids of heart mitochondria. Transition temperature obtained from the Arrhenius plots of respiration occurred at 21 and 24 degrees C for heart mitochondria of normal and hypophysectomized rats, respectively. Most notably, after hypophysectomy the rate of respiration was lower below 24 degrees C, but was progressively higher above that temperature when compared to normal rats. The energy of activation was 148 and 36% larger below and above the transition temperature, respectively. Growth hormone restored almost completely the energy of activation and respiratory rates to normal levels. Administration of L-thyroxine, with or without growth hormone, did not significantly change the rate of respiration but decreased the transition temperature to 17.7-17.9 degrees C. Lipid and phospholipid content, as well as percent distribution of phospholipids and their fatty acid composition were not statistically different among the different groups of rats. Only cholesterol content was increased after hypophysectomy. Administration of growth hormone and thyroxine did not significantly change the total unsaturation index of fatty acids, but growth hormone increased the content of arachidonic acid (20 : 4) by 70% but decreased the docosahexaenoic acid (22 : 6) three times which may have a beneficial effect on mitochondrial membranes. These and other results suggest that hormones exert different effects on subcellular organelles in different tissues, like heart and liver.

Anilino Naphthalenesulfonates↗

PubMed2002

Antiferromagnetic order induced by an applied magnetic field in a high-temperature superconductor.

One view of the high-transition-temperature (high-Tc) copper oxide superconductors is that they are conventional superconductors where the pairing occurs between weakly interacting quasiparticles (corresponding to the electrons in ordinary metals), although the theory has to be pushed to its limit. An alternative view is that the electrons organize into collective textures (for example, charge and spin stripes) which cannot be 'mapped' onto the electrons in ordinary metals. Understanding the properties of the material would then need quantum field theories of objects such as textures and strings, rather than point-like electrons. In an external magnetic field, magnetic flux penetrates type II superconductors via vortices, each carrying one flux quantum. The vortices form lattices of resistive material embedded in the non-resistive superconductor, and can reveal the nature of the ground state-for example, a conventional metal or an ordered, striped phase-which would have appeared had superconductivity not intervened, and which provides the best starting point for a pairing theory. Here we report that for one high-Tc superconductor, the applied field that imposes the vortex lattice also induces 'striped' antiferromagnetic order. Ordinary quasiparticle models can account for neither the strength of the order nor the nearly field-independent antiferromagnetic transition temperature observed in our measurements.

Journal Article↗

PubMed1988

NMR study of the interactions of polymyxin B, gramicidin S, and valinomycin with dimyristoyllecithin bilayers.

The interactions of three polypeptide antibiotics (polymyxin B, gramicidin S, and valinomycin) with artificial lecithin membranes were studied by nuclear magnetic resonance (NMR). Combination of 31P and 2H NMR allowed observation of perturbations of the bilayer membrane structure induced by each of the antibiotics in the regions of the polar headgroups and acyl side chains of the phospholipids. The comparative study of the effects of these membrane-active antibiotics and the lipid bilayer structure demonstrated distinct types of antibiotic-membrane interactions in each case. Thus, the results showed the absence of interaction of polymyxin B with the dimyristoyllecithin membranes. In contrast, gramicidin S exhibited strong interaction with the lipid above the gel to liquid-crystalline phase transition temperature: disordering of the acyl side chains was evident. Increasing the concentration of gramicidin S led to disintegration of the bilayer membrane structure. At a molar ratio of 1:16 of gramicidin S to lecithin, the results are consistent with coexistence of gel and liquid-crystalline phases of the phospholipids near the phase transition temperature. Valinomycin decreased the phase transition temperature of the lipids and increased the order parameters of the lipid side chains. Such behavior is consistent with penetration of the valinomycin molecule into the interior of the lipid bilayers.

Dimyristoylphosphatidylcholine↗

PubMed1975

Physical studies on phosphonium phosphatidylcholine. A unique [31P]phosphorus nuclear-magnetic-resonance probe for model and biological membranes.

1. Distearoyl phosphatidylcholine and the phosphonium analogue, in which the nitrogen atom is replaced by phosphorus, show similar gel-liquid crystalline transition temperatures as detected by differential scanning calorimetry. 2. The temperature-dependence of the 31P n.m.r. (nuclear-magnetic-resonance) linewidths of the phosphate resonances of sonicated vesicles of distearoyl phosphatidylcholine and the phosphonium analogue are similar. Below the phase-transition temperature the linewidths decrease as the temperature is raised. Above the phase-transition temperature the phosphate resonances are relatively temperature-independent. The phosphonium 31P n.m.r. signal exhibits the same pattern of temperature-dependence. 3. The 31P n.m.r. phosphonium resonance is sensitive to the paramagnetic shift reagent, K3Fe(CN)6. Use of K3Fe(CN)6, together with Nd(NO3)3, enabled the determination of the trans-bilayer distribution of egg-yolk phosphatidylcholine and its phosphonium analogue in co-sonicated vesicles. Both are distributed comparably across the bilayer of the vesicles. 4. The phosphonium 31P n.m.r. signal is much sharper than the corresponding phosphate resonance in both sonicated and unsonicated dispersions of the phosphatidylcholine analogue. 5. The properties of the phosphonium analogue of phosphatidylcholine are discussed in terms of its suitability as a probe of membrane structure.

Calorimetry↗

PubMed2004

Investigation of temperature-induced phase transitions in DOPC and DPPC phospholipid bilayers using temperature-controlled scanning force microscopy.

Under physiological conditions, multicomponent biological membranes undergo structural changes which help define how the membrane functions. An understanding of biomembrane structure-function relations can be based on knowledge of the physical and chemical properties of pure phospholipid bilayers. Here, we have investigated phase transitions in dipalmitoylphosphatidylcholine (DPPC) and dioleoylphosphatidylcholine (DOPC) bilayers. We demonstrated the existence of several phase transitions in DPPC and DOPC mica-supported bilayers by both atomic force microscopy imaging and force measurements. Supported DPPC bilayers show a broad L(beta)-L(alpha) transition. In addition to the main transition we observed structural changes both above and below main transition temperature, which include increase in bilayer coverage and changes in bilayer height. Force measurements provide valuable information on bilayer thickness and phase transitions and are in good agreement with atomic force microscopy imaging data. A De Gennes model was used to characterize the repulsive steric forces as the origin of supported bilayer elastic properties. Both electrostatic and steric forces contribute to the repulsive part of the force plot.

1,2-Dipalmitoylphosphatidylcholine↗

PubMedDate not supplied

Thermal stability of DNA interacting with furazolidone and Cu(II) ions.

Furazolidone, on complexing with DNA, led to its thermal stabilization. The increase in transition temperature of DNA (delta Tm) increased linearly with % A--T content. Increasing concentration of Cu(II) ions progressively lowered the transition temperature of DNA, but Cu(II) ions were not equally effective in lowering the transition temperature of furazolidone-DNA complex. When equimolar amounts of Cu(II) ions and furazolidone were used, the stabilisation effects of furazolidone prevailed over the destabilisation effect of Cu(II) ions.

Animals↗

PubMed1983

Tumor promoter 12-O-tetradecanoylphorbol 13-acetate alters state, fluidity and hydration of 1,2-diacyl-sn-glycero-3-phosphocholine bilayers.

Previous results (Castagna et al. (1979) FEBS Lett. 100, 62-66; Fisher et al. (1979) Biochem. Biophys. Res. Commun. 86, 1063-1068) indicated us that the active tumor promoter TPA (12-O-tetradecanoylphorbol 13-acetate) decreased fluorescence polarisation of diphenylhexatriene in lymphoblastoid and rat embryo cells. In the present study, experiments aimed at examining the molecular interactions of tumor promoters with cell membrane components are performed with fully hydrated multibilayers of 1,2-diacyl-sn-glycero-3-phosphocholine (DPPC) into which increasing amounts of TPA are inserted. The thermotropic behaviour of both the phospholipid bilayers and the interbilayer water was investigated using the differential scanning calorimetry (DSC) and the approach of Ter-Minassian-Saraga et al. ((1982) J. Colloïd Interface Sci. 81, 369-383). The major effects of the tumor promoter are confined to concentrations up to 20% mol fractions of TPA. In this range of concentrations the incorporation of TPA into liposomes decreases the phase-transition temperature but did not affect delta HDPPC. Furthermore TPA increases the hydration of the multibilayers. Above 20% mol fractions of TPA, a different thermal behaviour of the system which might suggest morphological rearrangements was observed. The lipid state in TPA-treated liposomes was monitored by fluorescence polarisation using diphenylhexatriene as a lipophilic fluorescent probe and the phase-transition temperature was calculated. The phase transition temperatures determined by both methods were in good agreement. The lowering of this temperature and the decay of fluorescence anisotropy of diphenylhexatriene were parallel. Those effects are consistent with the "fluidising' effect of TPA on DPPC.

Calorimetry, Differential Scanning↗

PubMed1992

Pulmonary surfactant secretion is regulated by the physical state of extracellular phosphatidylcholine.

Pulmonary alveolar type II cells synthesize, secrete, and recycle the components of pulmonary surfactant. In this report we present evidence that dipalmitoylphosphatidylcholine is a potent inhibitor of surfactant lipid secretion by type II cells. Monoenoic and dienoic phosphatidylcholines with fatty acids of 16 or 18 carbons are ineffective as inhibitors of surfactant lipid secretion. In contrast, disaturated phosphatidylcholines, with either symmetric or asymmetric pairs of fatty acids of 14, 16, or 18 carbons, exhibit inhibition of surfactant secretion that correlates extremely well with the phase transition temperature (Tc) of the phospholipid. The inhibitory activity of dipalmitoylphosphatidylcholine is not dependent upon lipid stereochemistry. N-Methylated derivatives of dipalmitoylphosphatidylethanolamine are significantly less effective than phosphatidylcholine as inhibitors. Phosphatidylcholines below their phase transition temperature are inhibitors of surfactant secretion, whereas those above their phase transition temperature are either ineffective or weakly inhibitory. The phase transition dependence of inhibition is observed when type II cells are incubated at 37 degrees C with different species of phosphatidylcholine. In addition, if type II cells are stimulated to secrete at different temperatures the efficacy of a given phospholipid as an inhibitor is dependent on its relationship to Tc (i.e. dipalmitoylphosphatidylcholine with a Tc of 41 degrees C significantly inhibits secretion at 37 degrees C but not at 42 degrees C). Inhibition of surfactant secretion by dipalmitoylphosphatidylcholine is abrogated when it is incorporated into the same liposome with dioleoylphosphatidylcholine as a 50:50 mixture. In contrast, the simultaneous addition of two separate populations of liposomes, one composed of dipalmitoylphosphatidylcholine and the other composed of dioleoylphosphatidylcholine, does not significantly alter the inhibitory activity found with dipalmitoylphosphatidylcholine alone. These data provide compelling evidence that the physical state of phosphatidylcholine can regulate surfactant secretion from alveolar type II cells and suggest a unique mechanism for regulating exocytosis in the alveolus of the lung.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1979

Conformational stability of ribonuclease T1. I. Thermal denaturation and effects of salts.

The thermal transition of RNase T1 was studied by two different methods; tryptophan residue fluorescence and circular dichroism. The fluorescence measurements provide information about the environment of the indole group and CD measurements on the gross conformation of the polypeptide chain. Both measurements at pH 5 gave the same transition temperature of 56 degrees C and the same thermodynamic quantities, delta Htr (= 120 kcal/mol) and delta Str (= 360 eu/mol), for the transition from the native state to the thermally denatured state, indicating simultaneous melting of the whole molecule including the hydrophobic region where the tryptophan residue is buried. Stabilization by salts was observed in the pH range from 2 to 10, since the presence of 0.5 m NaCL caused an increase of about 5 degrees C to 10 degrees C in the transition temperature, depending on the pH. The fluorescence measurements on the RNase T1 complexed with 2'-GMP showed a transition with delta Htr =167 kcal/mol and delta Str =497 eu/mol at a transition temperature about 6 degrees C higher than that for the free enzyme. The large value of delta Htr for RNase T1 indicates the highly cooperative nature of the thermal transition; this value is much higher than those of other globular proteins. Analysis of the CD spectrum of thermally denatured RNase T1 suggests that the denatured state is not completely random but retains some ordered structures.

Circular Dichroism↗

PubMed1979

The influence of charge on bilayer membranes. Calorimetric investigations of phosphatidic acid bilayers.

The pH-dependence of the phase transition of dimyristoyl phosphatidic acid and dihexadecyl phosphatidic acid has been investigated using differential scanning calorimetry. Varying the pH induces different degrees of ionization of the polar head group. The changes in transition temperature with pH as observed by calorimetry are in good agreement with those obtained by measuring the changes in light scattering, whereas the transition temperatures reported by the fluorescent probe N-phenylnaphthylamine do not always coincide with those determined from calorimetry [1]. The observed maximum of the transition temperature at pH 3.5 corresponds to a minimum in the transition enthalpy vs. pH diagram. At this pH a particular stable bilayer phase is formed. Full protonation of phosphatidic acids leads to suspensions of mycrocrystals. The transition enthalpy approaches the value of the melting enthalpy of crystalline anhydrous phosphatidic acid. The decrease in the transition enthalpy at high pH values is due to a change in the hydrocarbon chain interactions induced by the doubly charged head groups. The cooperativity of the transition varies with the degree of ionization of the head group, being lower for doubly charged phosphatidic acids.

Calorimetry, Differential Scanning↗

PubMed2004

Synthesis and characterization of partially biodegradable and thermosensitive hydrogel.

A partially biodegradable and thermosensitive hybrid hydrogel network (DAN series) based on dextran-allylisocyanate (Dex-AI) and poly(N-isopropylacrylamide) (PNIPAAm) was synthesized via UV photocrosslinking. These hybrid hydrogels were characterized in terms of their chemical structure, thermal, mechanical, morphological and temperature-induced swelling properties. The effect of the composition ratio of Dex-AI to PNIPAAm on such properties were examined. The differential scanning calorimetry data show that this Dex-AI/PNIPAAm hybrid network has an increased lower critical solution temperature (LCST) and glass transition temperature (Tg) with an increase in the Dex-AI content. The interior morphology of these hybrid hydrogels revealed a decreased porous microstructure with an increase in the Dex-AI content in the hybrid network. Furthermore, if the Dex-AI composition became too high, a distinctive network structure with two different microporous structures appeared. The mechanical properties of these hybrid hydrogels also increased with an increase in the Dex-AI content. The temperature dependence of the swelling ratio, the deswelling kinetics as well as the reswelling kinetics was also characterized by gravimetric method. When comparing with a normal PNIPAAm hydrogel, these Dex-AI/PNIPAAm hybrid networks, due to the presence of Dex-AI moiety, also show improved temperature-induced intelligent properties, such as the faster and controllable response dynamics, which may find promising applications in a wide variety of fields, such as biomedical and bioengineering fields.

Absorbable Implants↗

PubMed2006

Crystallization inhibition of an amorphous sucrose system using raffinose.

The shelf life of pure amorphous sucrose systems, such as cotton candy, can be very short. Previous studies have shown that amorphous sucrose systems held above the glass transition temperature will collapse and crystallize. One study, however, showed that adding a small percent of another type of sugar, such as trehalose, to sucrose can extend the shelf life of the amorphous system by slowing crystallization. This study explores the hypothesis that raffinose increases the stability of an amorphous sucrose system. Cotton candy at 5 wt% raffinose and 95 wt% sucrose was made and stored at room temperature and three different relative humidities (%RH) 11%RH, 33%RH, and 43%RH. XRD patterns, and glass transition temperatures were obtained to determine the stability as a function of %RH. The data collected showed that raffinose slows sucrose crystallization in a low moisture amorphous state above the glass transition temperature and therefore improves the stability of amorphous sucrose systems.

Chemistry↗

PubMed1979

Motion of the lengthened zwitterionic head groups of C16-lecithin analogues in aqueous solutions as studied by dielectric relaxation measurements.

Phosphatidyl choline analogues with increased phosphate-trimethylammonium distance were synthesized and aqueous solutions of these bilayer forming phospholipids were prepared. Dielectric spectra of the solutions were measured at several temperatures around the crystalline/liquid-crystalline phase transition temperature of the samples. The observed data are treated in terms of a Debye relaxation function and also of a relaxation function based on a theoretical model of the aqueous solutions of multibilayer vesicles. As a noteworthy result, a pronounced cooperativity effect in the diffusive motions of the zwitterionic head groups emerges. The degree of cooperativity depends on the radius of curvature of the multibilayer vesicles and also on the length of the phospholipid zwitterions. The values for the mobility of the trimethylammonium group are of the same order of magnitude as those for the mobility of whole phospholipid molecules in its lateral diffusive motion. Indications for a phase transition at a temperature above the main transition temperature are found with solutions of C16- lecithin analogues with 9 and 10 methylene groups between the phosphate and the trimethylammonium group.

Journal Article↗

PubMedDate not supplied

[Effect of bivalent cations on the temperature of phase transition in lipid membranes].

A theory is developed which explains the temperature shift of phase transition of bilayer delta Tc resulting from the interaction of charged polar heads of lipid molecules. It has been shown that adsorption of monovalent cations on the strongly charged membrane increases the transition temperature by about 15 degrees, this value being independent of the ionic strength and dielectric permeability epsilon of the medium. When divalent cations are adsorbed the temperature shift of transition is larger, the value delta Tc depending on medium epsilon, where the polar heads are located. If the membrane is in the electrolyte solution delta Tc approximately equal to 19 degrees; when a dehydrated contact with low dielectric permeability is initiated between the membranes, the transition temperature in this zone is to increase by about 160 degrees, which well agrees with the experimental data.

Calcium↗