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PubMed2003

The physical state of the LDL core influences the conformation of apolipoprotein B-100 on the lipoprotein surface.

We assessed the influence of temperature on the secondary structure of apolipoprotein B-100 (apoB) in normal low-density lipoprotein (N-LDL) and triglyceride-rich LDL (T-LDL). Gradual heating from 7 degrees C to the phase-transition temperature of the lipoprotein core ( approximately 28 degrees C and approximately 15 degrees C for N-LDL and T-LDL, respectively) gradually altered the secondary structure of apoB, while further heating from the phase-transition temperature to 45 degrees C had no additional effect. Above the phase-transition temperature of the core, the apoBs of N-LDL and T-LDL had a similar secondary structure. These results indicate that the conformation of apoB on the LDL surface depends strongly on the physical state of the lipoprotein core, and less on the lipid composition of the core per se.

Apolipoprotein B-100↗
PubMed1986

Partition of chlorpromazine into lipid bilayer membranes: the effect of membrane structure and composition.

Partition coefficients, kp, of chlorpromazine between the aqueous phase and lipid bilayer vesicles were determined as function of drug concentration, lipid chain length, cholesterol content and temperature encompassing the range of the lipid phase transition. Radioactivity and absorption measurements were performed to determine the kp values. Up to a concentration of 3 . 10(-5) M, the partition coefficient is independent of chlorpromazine concentration, whereas it decreases drastically at higher chlorpromazine concentrations, at which membrane lysis is observed. Membrane structure is not disturbed at less than 3 . 10(-5) M chlorpromazine, as was concluded from electron paramagnetic resonance studies measuring TEMPO partitioning and order degree. However, the lipid phase-transition temperature decreases and is broadened at higher chlorpromazine concentrations. From fluorescence measurements, we conclude the formation of chlorpromazine micelles at concentrations higher than 5 . 10(-5) M in chlorpromazine in the absence of lipids and the formation of mixed micelles in the presence of lipids. The effect of lipid chain length on kp values was investigated. The partition coefficient decreases from 8100 in dilauroyl- to 3400 in dipalmitoylphosphatidylcholine vesicles, both at 50 degrees C, that is, above their corresponding phase-transition temperature tt. At t less than tt the kp values are strongly reduced, by at least a factor of 10, depending on lipid chain length and membrane composition. It is possible to establish a lipid phase-transition curve from the temperature-dependent measurements of the kp values. Cholesterol within the lipid membrane strongly decreases kp. At 20 mol% cholesterol in dipalmitoylphosphatidylcholine membranes, the partition coefficient is reduced from 3400 to 2300. This value is well comparable to the kp value obtained in erythrocyte ghosts. In contradiction to earlier experiments by Conrad and Singer (Biochemistry 20 (1981) 808-818), this value in a biological membrane could be obtained by the hygroscopic desorption as well as the centrifugation method. From our experiments we are justified in further considering artificial bilayer membranes as models for biological membranes.

Chemical Phenomena↗
PubMed1983

Temperature dependence of D-glucose transport in reconstituted liposomes.

Sodium-dependent D-glucose uptake into proteoliposomes reconstituted from dimyristoylphosphatidylcholine (DMPC) and hog kidney brush border membrane extract is strongly affected by temperature and the physical state of the membranes. This dependence is defined by a nonlinear Arrhenius plot with a break point at 23 degrees C, a temperature not significantly different from the phase transition temperature of the pure lipid (24 degrees C). The transport process is characterized by different activation energies: 35.1 kcal/mol below and 5.5 kcal/mol above the transition temperature. The shift in the break point for the D-glucose transport activity from 15 degrees C, in the brush border membranes, to 23 degrees C in the reconstituted system leads us to conclude that the lipids surrounding the sodium/D-glucose cotransport system can exchange readily with the bulk lipid used for reconstitution. The results thus provide no evidence for the presence of an annulus of specific lipids surrounding the transport system.

Animals↗
PubMed1992

Degradation of five polyurethane gastric bubbles following in vivo use: SEC, ATR-IR and DSC studies.

Five Garren-Edwards Gastric Bubbles were characterized, following up to 4 months use in vivo, using size exclusion chromatography, differential scanning calorimetry and attenuated total reflectance infrared spectroscopy. These techniques show that the material used to construct the bubble is probably an aromatic polyester urethane and revealed a 39-55% decrease in number average molecular weight, a 9 degrees C decrease in glass transition temperature, the disappearance of soft segment crystallinity and a broadening of the hard segment melting region after exposure to highly acidic (approximately pH 1.2) gastric fluid. The results indicate that significant chemical and morphological changes have taken place in the bubble material, including loss in chemical functionality, phase separation and increased hard segment aggregation. A comparison of the decrease in glass transition temperature as a function of molecular weight suggests that glass transition temperature is a sensitive predictor of this material's stability. Additionally, evidence is provided that the broad infrared absorption at 1077-1067 cm-1 normally assigned to C-O-C hard segment may represent two types of C-O-C stretching: (1) C-O-C stretching of the free urethane carbonyl, and (2) C-O-C stretching of the hydrogen bonded urethane carbonyl.

Biodegradation, Environmental↗
PubMed1995

Differences in the thermal stability of acclimation temperature-associated types of carp myosin and its rod on differential scanning calorimetry.

Differential scanning calorimetry (DSC) was employed for studying the thermal unfolding of myosin and its rod part prepared from carp acclimated to 10 and 30 degrees C. Differences in the thermal stability reflecting structural properties were clearly demonstrated by the DSC data obtained at pH 8.0 in 0.6 M KCl for the two types of carp myosin and rod. The transition temperatures on myosin and rod given by the major peaks for the 10 degrees C-acclimated carp were 33.9 and 47.4 degrees C and 33.0 and 44.0 degrees C, respectively, assuming two endotherms for this type. Since the shape of the first peaks at 33.9 and 33.0 degrees C was not symmetrical, two peaks having similar transition temperatures overlapped in this temperature range. When the data were analyzed using three endotherms, the three transition temperatures obtained for myosin and rod were 32.8, 34.9, and 47.4 degrees C and 32.9, 33.4, and 44.1 degrees C, respectively. Thus, the position of the first peak for the 10 degrees C-acclimated carp myosin did not change even after removal of the large subfragment-1 part, but the transition of the second peak shifted to a lower temperature by about 3 degrees C. The myosin and rod from carp acclimated to 30 degrees C showed three distinct peaks at 35.9, 39.7, and 49.1 degrees C and 34.5, 39.7, and 46.7 degrees C, respectively. The position of the largest peak for myosin remained unchanged, and the shift of the peak position of the highest temperature was about 3 degrees C, as obtained for the 10 degrees C-acclimated carp.(ABSTRACT TRUNCATED AT 250 WORDS)

Acclimatization↗
PubMed1987

Investigations into the polymorphism of lipid A from lipopolysaccharides of Escherichia coli and Salmonella minnesota by Fourier-transform infrared spectroscopy.

The polymorphism of lipid A, the endotoxic principle of the lipopolysaccharides of gram-negative bacteria, has been investigated in the fully hydrated state at temperatures between 5 degrees and 58 degrees C via Fourier-transform infrared spectroscopy. These measurements were supplemented by X-ray diffraction, fluorescence intensity techniques and differential thermal analysis. Up to three distinct phase transitions could be detected, with the main transition temperatures lying at approximately 41 degrees, 46 degrees, 44 degrees and 47 degrees C for Escherichia coli lipid A, Salmonella minnesota lipid A, and the synthetic lipid A compounds 506 and 516, respectively. 4'-Monophosphoryl-lipid A samples exhibited their main transition temperatures at considerably higher temperatures (about 52 degrees C for E. coli lipid A). The analysis of greater than CH2 stretching absorption bands as well as the wide-angle scattering behaviour of the lipid A samples showed that the main transition apparently involved the completion of hydrocarbon chain melting of lipid A, as typically observed for phospholipids. However, the phase transition behaviour was found to be much more complex than that usually observed for model phospholipid systems. Even below the main transition temperature, considerable amounts of the methylene segments of the acyl chains of lipid A were found to assume gauche conformations. These conformational changes might be related to the occurrence of up to two further transitions located at about 22 degrees, 30 degrees, 27 degrees and 25.5 degrees C (first transition) and at about 34 degrees, 42 degrees, 38.5 degrees and 40.5 degrees C (second transition) for E. coli lipid A, S. minnesota lipid A and the synthetic lipid A compounds 506 and 516, respectively. Furthermore, by the analysis of some characteristic infrared absorption bands related to the hydrophilic backbone, it could be demonstrated that the temperature-induced conformational changes occurring within the hydrocarbon chains were constantly and simultaneously accompanied by detectable rearrangements within the interfacial region and the polar head group of lipid A. The following conclusions were drawn: Up to about 30 degrees C the lipid A assemblies were supposed to adopt virtually bilayered, true lamellar arrangements, as revealed by the analysis of greater than CH2 scissoring vibrations and X-ray diffraction pattern. However, as indicated by fluorometric techniques, no stable closed vesicles seemed to be formed even under these conditions.(ABSTRACT TRUNCATED AT 400 WORDS)

Calorimetry↗
PubMed2004

The effect of production regime and crucible materials on the thermal properties of sodium phosphate glasses produced from salts.

Changes in the thermal properties of sodium phosphate glasses during melt production have been investigated using Pt/Au and fused alumina crucibles. Glasses were produced from NaH(2)PO(4) as a starting material, providing an intrinsic Na(2)O:P(2)O(5) ratio of 1:1 and giving an O/P = 3, that is, a metaphosphate. In Pt/Au crucibles, glass transition temperatures rose to a plateau value of 295 degrees C at a rate determined by melt temperature. No contamination of the glass by platinum or gold was detected or indicated in the results. E(a) for the reaction was found to be 66.4 kJ mol(-1). In fused alumina crucibles, glass transition temperatures rose to over 450 degrees C, with these values showing some convergence at higher furnace temperatures. Extensive erosion of the alumina crucibles was observed. The amount of alumina incorporation within the glasses correlated well with the rise in glass transition temperature up to a maximum of 15.5 mol % Al(2)O(3) content. Al(2)O(3) incorporation above this value caused a reduction in the value of the T(g).

Aluminum Oxide↗
PubMed1999

Glass transition of wheat gluten plasticized with water, glycerol, or sorbitol.

The glass transition temperature of wheat gluten, plasticized with water, glycerol, or sorbitol, has been studied using dynamical mechanical thermal analysis. For the three plasticizers studied, the general behavior of the glass transition temperature broadly followed the Couchman-Karasz relation using a wheat gluten DeltaC(p)() of 0.4 J g(-)(1) K(-)(1). Compared on such a fractional weight basis, it could be concluded that the plasticizing effect of glycerol and sorbitol on wheat gluten proteins is less important than the plasticizing effect of water. A continuous curve was obtained with the three plasticizers when the evolution of the glass transition temperature was presented on a fractional molecular basis. This was related to the similar chemical structure of these three components containing hydroxyl groups.

Calorimetry, Differential Scanning↗
PubMed1990

A ligand-induced, temperature-dependent conformational Change in penicillopepsin. Evidence from nonlinear Arrhenius plots and from circular dichroism studies.

The effect of temperature on the rate constants of hydrolysis of various substrates by penicillopepsin is dependent on the length of the substrate. For the series Ac-(Ala)m-Lys-Nph-(Ala)n-amide (where Ac- is acetyl- and Nph- is p-nitrophenylalanyl-), where m and n = 0-2, substrates lacking both P'2 and P3 residues give linear Arrhenius plots with an energy of activation of about 55 kJ.mol-1. The Arrhenius plots of substrates in which an alanine residue occupies P'2 show a sharp break at an average transition temperature of 10.5 degrees C. The activation energies are approximately 90 kJ.mol-1 below and approximately 54 kJ.mol-1 above the transition temperature, respectively. For substrates in which P3 is occupied, the average transition temperature is 14.2 degrees C. In this case, the activation energies are 66 kJ.mol-1 below and from 26 to 39 kJ.mol-1 above the transition point. The most probable explanation of these phenomena is that substrate interaction at subsites S3 and/or S'2 of the enzyme induces a temperature-dependent conformational change. Physical evidence for this comes from the observation that the temperature dependence of a CD absorption band at 242 nm of a penicillopepsin-pepstatin complex shows a sharp break that corresponds to those observed in the Arrhenius plots of substrates with alanine at P'2 and P3, whereas the same CD band in the free enzyme is linearly dependent on temperature.

Amino Acid Sequence↗
PubMed1996

The effect of side-chain analogues of cholesterol on the thermotropic phase behavior of 1-stearoyl-2-oleoylphosphatidylcholine bilayers: a differential scanning calorimetric study.

In this study we have examined the effects of analogues of cholesterol differing with respect to alkyl side-chain length and structure on the thermotropic phase behavior of bilayers formed from 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC), an important subclass of naturally occurring phosphatidylcholines (PCs). The synthetic sterols we studied contained either a terminally unbranched (n-series) or a single methyl-branched (iso-series) side chain of 3 to 10 carbon atoms. The phase transition behavior was examined by high-sensitivity differential scanning calorimetry (DSC). The main phase transition endotherm of SOPC/sterol bilayers consists of superimposed sharp and broad components, which represent the hydrocarbon chain melting of sterol-poor and sterol-rich phospholipid domains, respectively. The transition temperature and the cooperativity of the sharp component are moderately reduced upon sterol incorporation and the enthalpy decreases to zero when sterol levels of 20-30 mol% are reached. The enthalpy of the broad component transition initially increases to a maximum around 25 or 25-30 mol% sterol and thereafter decreases with further increases in sterol concentration. However, the broad transition of SOPC bilayers containing both short (C-22, i-C5 and n-C3) and long (i-C9 and i-C10) side-chain sterols still persists at levels of 50 mol% sterol. Thus the effective stoichiometry of SOPC-sterol interactions varies with changes in sterol alkyl side-chain length. The incorporation of short linear or branched side-chain sterols (C-22, n-C3, n-C4, i-C5) causes the broad component transition temperature and cooperativity to decrease dramatically, whereas the incorporation of medium- and long-chain sterols in both the n- and iso-series has less effect on the transition temperature and cooperativity of the broad component. Overall, no significant differences were found between the n- and iso-series sterols for a given side-chain length. A comparison of the phase behavior of dipalmitoylphosphatidylcholine (DPPC)/sterol (McMullen et al. (1995) Biophys. J. 69, 169-176) and SOPC/sterol mixtures indicates that the primary factor responsible for changes in the thermotropic phase behavior of these systems is the extent of the hydrophobic mismatch between the sterol and the host lipid bilayer. However, sterol miscibility in PC bilayers, and thus the stoichiometry of lipid-sterol interactions, also appears to depend on the degree of unsaturation of the host lipid bilayer.

Calorimetry, Differential Scanning↗
PubMed1993

Differential scanning calorimetric study of 5-enolpyruvoyl shikimate-3-phosphate synthase and its complexes with shikimate-3-phosphate and glyphosate: irreversible thermal transitions.

The thermal denaturation of native Escherichia coli 5-enolpyruvoyl shikimate-3-phosphate (EPSP) synthase, its binary complex with shikimate-3-phosphate (S3P) and its ternary complex with S3P and glyphosate have been studied using highly-sensitive differential scanning calorimetry (DSC). All observed transitions are strongly scanning-rate-dependent and irreversible. Consistent with these observations, the data were better fit by a simple irreversible model than by the controversial reversible model more commonly employed. The results obtained provide additional support for the application of irreversible models to the thermal denaturation of proteins. The calculated parameters, activation energy (Ea), enthalpy of denaturation (delta H) and transition temperature (Tm), obtained from fitting to an irreversible model agree well with values obtained from approximation techniques. Further, the results show that the formation of the ternary complex greatly enhances the thermal stability of the enzyme (delta Tm = 10.6 degrees C), while the binding of S3P alone increases the transition temperature only slightly (delta Tm = 3 degrees C). The heat of binding calculated at the transition temperature also demonstrates the greater stability of the ternary complex (delta H = -70 kcal/mol) versus the binary complex (delta H = -10 kcal/mol).

3-Phosphoshikimate 1-Carboxyvinyltransferase↗
PubMed1984

Ultrasonic evidence for structural relaxation in large unilamellar liposomes.

The ultrasonic absorption of large unilamellar vesicles (average diameter 0.2 micron) was determined in the frequency range 0.5-5 MHz. The liposomes were composed of a 4:1 mixture by weight of dipalmitoyl phosphatidylcholine and dipalmitoyl phosphatidylglycerol. They were studied with and without cholesterol or gramicidin incorporated into the bilayer. A large increase in absorption occurs at the solid to liquid-crystalline phase transition temperature (42 degrees C) of the pure lipid vesicles. This increase in absorption is interpreted as a structural relaxation of the 'melting' fatty acid chains occurring with an average relaxation time of 76 ns. The liposomes were also found to be extremely permeable near the transition temperature. Essentially complete release of cytosine arabinoside, a small water-soluble molecule, occurred at 42 degrees C. Addition of cholesterol or gramicidin to the bilayer of the liposomes broadened the ultrasonic absorption and reduced the efflux of cytosine arabinoside at the phase transition. No increase in absorption was observed at the transition temperature in the presence of 50 mol% of cholesterol. Gramicidin, in addition to broadening the transition, slows the isomerization of bonds in the hydrocarbon chains of the lipids. A concentration of 5 mol% gramicidin increased the average relaxation time to 211 ns.

Cytarabine↗
PubMed1984

Temperature-dependent drug release from large unilamellar liposomes.

The drug-release properties of large unilamellar liposomes were measured at temperatures near the lipid's phase-transition temperature. The liposomes were formed from a mixture of dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylglycerol (4:1 by weight) by the reverse-phase evaporation process. These liposomes captured 25-35% of the radiolabeled anticancer drug cytosine [3H]-1-beta-arabinofuranoside in their aqueous compartment. They were stable in serum below the lipid's phase-transition temperature of 41 degrees C. Complete drug release occurred within seconds after the liposomes reached a temperature of 43 degrees C in serum. Addition of cholesterol or phosphatidylglycerol to the liposomal membrane reduced the drug-release temperature and broadened the range of drug release. These results show that suspensions of large unilamellar liposomes can be made to encapsulate a therapeutically useful quantity of drug that is rapidly and completely released at 43 degrees C in serum.

Blood↗
PubMed2004

Effect of variations in the structure of a polyleucine-based alpha-helical transmembrane peptide on its interaction with phosphatidylethanolamine Bilayers.

High-sensitivity differential scanning calorimetry and Fourier transform infrared spectroscopy were used to study the interaction of a cationic alpha-helical transmembrane peptide, acetyl-Lys2-Leu24-Lys2-amide (L24), and members of the homologous series of zwitterionic n-saturated diacyl phosphatidylethanolamines (PEs). Analogs of L24, in which the lysine residues were replaced by 2,3-diaminopropionic acid (acetyl-DAP2-Leu24-DAP2-amide (L24DAP)) or in which a leucine residue at each end of the polyleucine sequence was replaced by a tryptophan (Ac-K2-W-L22-W-K2-amide (WL22W)), were also studied to investigate the roles of lysine side-chain snorkeling and aromatic side-chain interactions with the interfacial region of phospholipid bilayers. The gel/liquid-crystalline phase transition temperature of the PE bilayers is altered by these peptides in a hydrophobic mismatch-independent manner, in contrast to the hydrophobic mismatch-dependent manner observed previously with zwitterionic phosphatidylcholine (PC) and anionic phosphatidylglycerol (PG) bilayers. Moreover, all three peptides reduce the phase transition temperature to a greater extent in PE bilayers than in PC and PG bilayers, indicating a greater disruption of PE gel-phase bilayer organization. Moreover, the lysine-anchored L24 reduces the phase transition temperature, enthalpy, and the cooperativity of PE bilayers to a much greater extent than DAP-anchored L24DAP, whereas replacement of the terminal leucines by tryptophan residues (Ac-K2-W-L22-W-K2-amide) only slightly attenuates the effects of this peptide on the chain-melting phase transition of the host PE bilayers. All three peptides form very stable alpha-helices in PE bilayers, but small conformational changes occur in response to mismatch between peptide hydrophobic length and gel-state lipid bilayer hydrophobic thickness. These results suggest that the lysine snorkeling plays a significant role in the peptide-PE interactions and that cation-pi-interactions between lysine and tryptophan residues may modulate these interactions. Altogether, these results suggest that the lipid-peptide interactions are affected not only by the hydrophobic mismatch between these peptides and the host lipid bilayer but also by the electrostatic and hydrogen-bonding interactions between the positively charged lysine residues at the termini of these peptides and the polar headgroups of PE bilayers.

Binding Sites↗
PubMed2002

High-frequency dynamics of the glass former dibutylphthalate under pressure.

The high-frequency dynamics of a fragile molecular glass former (dibutylphthalate) was studied through inelastic x-ray scattering (IXS), as a function of pressure and temperature. The mesoscopic structural arrest associated with the glass transition process was tracked by following upon cooling the inelastic excitations at fixed Q points in the dispersion curves, at ambient pressure and 2 kbar. The application of pressure to this system induces an offset between the macroscopic glass transition temperature T(g) and the mesoscopic glass transition temperature, as determined from IXS. The concomitant fragility decrease of dibutylphthalate under pressure unveils that the stronger the glass former is, the more its mesoscopic dynamics differ from the macroscopic regime. This trend is interpreted as the signature of a nanoscopic inhomogeneous elastic network. Further aspects of this system are obtained when studying the temperature dependence of its nonergodicity factor f(Q)(T). The chemical specificity of the molecule is suggested to be responsible for the nonobservation of a critical temperature T(c) in dibutylphthalate up to approximately 300 K.

Journal Article↗
PubMed1975

The antagonistic effect of an inhalation anesthetic and high pressure on the phase diagram of mixed dipalmitoyl-dimyristoylphosphatidylcholine bilayers.

Several workers have shown that phase transition-related changes in membrane lipids have a profound effect on membrane-solvated protein function. This phase transition temperature dependence has been explained as resulting from the formation of lateral phase separations within the membrane bilayer. The present study demonstrates that a clinical concentration of an inhalation anesthetic produces changes in both the phase transition temperature of pure lipid bilayers and the lateral phase separation temperature of mixed dipalmitoyl- and dimyristoylphosphatidylcholine bilayers of a magnitude sufficient to influence protein function. It is further shown that pressure is able to antagonize the effect of the anesthetic on these transition temperatures. It is proposed that anesthetic action within nerve membranes may be the result of changes in the lateral phase separation-controlled environment of the membrane-solvated proteins essential to nerve function.

Anesthesia, Inhalation↗
PubMed1985

Acid- and calcium-induced structural changes in phosphatidylethanolamine membranes stabilized by cholesteryl hemisuccinate.

The membrane stabilization effect of cholesteryl hemisuccinate (CHEMS) and the sensitivity of the CHEMS-phosphatidylethanolamine membranes to protons and calcium ions were studied by differential scanning calorimetry, freeze-fracture electron microscopy, and 31P NMR. (1) At neutral pH, the addition of 8 mol % CHEMS to transesterified egg phosphatidylethanolamine (TPE) raised the lamellar-hexagonal transition temperature of TPE by 11 degrees C. Stable bilayer vesicles were formed when the incorporated CHEMS exceeded 20 mol %. (2) At a pH below 5.5, the protonation of CHEMS enhanced the formation of the hexagonal phase (HII) of TPE. At 25 mol % CHEMS the bilayer-hexagonal transition temperature was lowered by 30 degrees C at pH 4.5. (3) The endothermic acid-induced hexagonal hexagonal transition of TPE-CHEMS was suppressed at 35 mol % CHEMS. However, 31P NMR and electron microscopy indicated that a lamellar-hexagonal transition still occurred at this composition. (4) The main transition of TPE was not affected by the protonation of the incorporated CHEMS, indicating that no macroscopic phase separation occurred in TPE-CHEMS mixtures at low pH. (5) In contrast to the HII-promoting effect of H+, the neutralization of the negative charge on TPE-CHEMS by Ca2+ resulted in aggregates that remained in the lamellar structure even at the hexagonal transition temperature of TPE. It is suggested that calcium might form a complex between CHEMS in apposed bilayers. These results are related to the possible biological function of acidic cholesterol esters in biomembranes.

Calcium↗
PubMed2000

In vitro effects of sodium fluoride and sodium dichromate on dynamic properties of human erythrocyte membrane.

Sodium fluoride (NaF) and sodium dichromate (Na2Cr2O7) are two different toxic compounds which are used as a dental caries prophylactic and as an oxidising agent in various industrial areas, respectively. However, accidental fluoride and chromate poisoning is not a rare occurrence, even death may result from cardiac or respiratory failure. In the present work, alterations produced by NaF, Na2Cr2O7 and temperature changes in the molecular dynamics of the human erythrocyte membrane were studied, in vitro, by the spin-labelling ESR technique. Human intact erythrocyte cells spin labelled with 5- and 16-doxyl stearic acids (5-DSA and 16-DSA) and treated with 40 microM NaF and 5 microM Na2Cr2O7 at 37 degrees C were used to quantify membrane fluidity. This was performed by measuring the changes in the order parameter (S), correlation time (tau) and phase transition temperature using recorded electron spin resonance (ESR) spectra. Experimental results show that 5 microM Na2Cr2O7 and 40 microM NaF do not produce any significant effects on the order parameter of 5-DSA spin label while they cause appreciable changes in the correlation time of the same label. As for 16-DSA, while Na2Cr2O7 does not produce any measurable effect on the order parameter of this label, NaF does in a certain extent. Although weak, the effects of both compounds on the correlation time of 16-DSA are found to be well above the experimental error limits. Change in temperature was observed to alter significantly S and tau parameters which show biphasic character in the temperature range of 5-50 degrees C. Activation energies of the hydrocarbon chains above and below transition temperatures were also determined for untreated and NaF or Na2Cr2O7 treated erythrocyte cells and the effect of NaF and Na2Cr2O7 on these energies and transition temperatures were discussed.

Chromates↗