Coenzyme model reaction in lipid bilayers

Coenzyme model reactions, such as the H⁻ (H⁺ + 2e⁻) transfer from NADH models to triphenyl methane dyes, were investigated in the presence of lipid bilayers, for example, -α-dimyristoyl phosphatidyl choline and egg yolk lecithin. In the temperature dependence of the acceleration effect by the lipid bilayer, discontinuous points were observed, corresponding to the phase transition point such as gel-liquid crystal (T_c) or the segregation point (T_s). The T_c and T_s values of the bilayers varied with the reactant as a result of the difference of perturbing effect on the structure of the bilayers. The pressure effect on the transition point was also studied. Transition points such as T_c or T_s became higher with increasing pressure, and dT_c/dP or dT_s/dP was different for various bilayers. In the gel phase of the membrane, stereospecific reduction of malachite green was observed by chiral nicotinamide: the difference in the catalytic effect on the reduction rate between (R)- and (S)-dihydronicotinamides was larger in the gel phase than that in the liquid crystal phase or in the phase separated state, which suggests that the gel-state molecule can recognize the molecular structure better than the liquid-crystal state molecule.     

Phase transition into the metallic state in hypothetical (without molecules) dense atomic hydrogen

A simple physical model of the metal-dielectric (vapor-liquid) phase transition in hypothetical (without molecules) atomic hydrogen is proposed. The reason for such a transition is the quantum collective cohesive energy occurring due to quantum electron-electron exchange similar to the cohesive energy in the liquid-metal phase of alkali metals. It is found that the critical parameters of the transition are P _c ～ 41000 atm, ρ _c ～ 0.1 g/cm³, and T _c ～ 9750 K.     

The formation and annealing of structural defects in lipid bilayer vesicles

It is shown that sonication of phospholipid-water dispersions below the crystalline → liquid crystalline phase transition temperature (T_c) produces bilayer vesicles with structural defects within the bilayer membrane, which permit rapid permeation of ions and catalyze vesicle-vesicle fusion. These structural defects are annihilated simply by annealing the vesicle suspension above T_c. The rate of annealing was found to be slow, of the order of an hour for T = 3 °C above T_c, but annealing is complete within 10 min for T = 10 °C above T_c. It is proposed that these structural defects are fault-dislocations in the bilayer structure, which arise from a population defect in the distribution of the lipid molecules between the outer and inner monolayers, when small bilayer fragments reassemble to form the small bilayer vesicles during the sonication procedure. Such a population defect can only be remedied by lipid transport via the inside ? outside flip-flop mechanism, which would account for the slow kinetics of annealing observed even at 3 °C above the phase transition.     

Effects of temperature and lipid composition on the serum albumin-induced aggregation and fusion of small unilamellar vesicles

Small unilamellar vesicles of egg phosphatidylcholine (PC) or dimyristoylphosphatidylcholine, mixed with small unilamellar vesicles labelled with 2-(10-(1-pyrene)decanoyl)phosphatidylcholine, exhibit a constant average size and excimer to monomer (E/M) ratio for several hours when incubated at pH 3.6 at a temperature higher than the phase transition temperature (T_c) of the lipids. Addition of bovine serum albumin to this system produces a transient turbidity increase, a fast decrease in the E/M ratio, a partial loss of vesicle-entrapped [¹⁴C]sucrose and a measurable leak-in of externally added sucrose. Sepharose 4B filtration of the system demonstrates that the E/M ratio decrease is strictly paralleled by the formation of liposomes which exhibit a low E/M ratio and a hydrodynamic radius larger than that of small unilamellar vesicles. These data demonstrate that the E/M ratio decrease can be unequivocally ascribed to a vesicle-vesicle fusion process induced by serum albumin. The rate of serum-albumin induced fusion of small unilamellar vesicles is: (a) maximal at a stoichiometric ratio of approx. 2 albumins per vesicle: (b) sensitive to the nature of the lipid and; (c) not altered when human serum albumin replaces bovine serum albumin. The rate of albumin-induced fusion of dimyristoylphosphatidylcholine small unilamellar vesicles is higher below the T_c of the lipid and increases with temperature above the T_c. The formation of protein-bound aggregates with defined stoichiometries and a high local vesicle concentration, as well as changes in the local degree of hydration, are proposed to be the driving forces for the protein-induced vesicle fusion in this system.     

Neiella holothuriorum sp. nov., isolated from the gut of a sea cucumber Apostichopus japonicus

A Gram-stain negative, aerobic, rod-shaped bacterium, designated 126^T, was isolated from the intestinal content of a sea cucumber, Apostichopus japonicus, in China. Strain 126^T was found to grow optimally at 25–28 °C and pH 7.5–8.0 in marine 2216 E medium, with tolerance of 1–7% (w/v) NaCl. Strain 126^T is motile by means of one to several polar flagella. The dominant fatty acids of strain 126^T were identified as C_16:1 ω7c/C_16:1 ω6c (29.5%), C_18:1 ω7c/C_18:1 ω6c (19.8%) and C_16:0 (16.7%). The respiratory quinone was found to be Q-8. The polar lipid profile was found to be mainly composed of phosphatidylglycerol and phosphatidylethanolamine. The total length of the draft genome is approximately 4.2?×?10⁶ bp, encoding 3655 genes and 3576 coding sequences. The G?+?C content of the genomic DNA is 48.0%. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain 126^T belongs to the genus Neiella and is closely related to Neiella marina J221^T (96.5%). Genomic comparisons of 126^T to N. marina J221^T revealed that they had similar genome size, G?+?C content and complement of clusters of orthologous groups. However, average nucleotide identity and digital DNA–DNA hybridization values between strains126^T and N. marina J221^T was 75.5% and 19.7%, which could distinguish the strains. On the basis of these phenotypic and genotypic data, strain 126^T is concluded to represent a novel species, for which the name Neiella holothuriorum sp. nov. is proposed. The type strain is 126^T (=?GDMCC 1.2530^T?=?KCTC 82829^T).

     

Interaction of small molecules with phospholipid bilayer membranes: permeability studies

The passage of a phospholipid through the gel to liquid crystal phase transition is associated with an increase in the motional freedom of its fatty acyl chains as measured by spectroscopic techniques and an essentially isothermal absorption of heat as measured by differential scanning calorimetry (DSC). In addition, bilayers formed from that phospholipid display a permeability maximum for both non-electrolytes and electrolytes in the temperature region of the phase transition. In this study the sodium (and in some cases glucose) permeabilities of liposomes composed of either dimyristoyl or dipalmitoyl phosphatidylcholine plus dicetylphosphate were measured in the presence of a group of benzene and adamantane derivatives known to increase fatty acyl chain motion below the lipid transition temperature (T_c) and in the case of the adamantanes to also lower the T_c as measured by DSC. None of these compounds change the temperature at which the permeability maximum occurs despite their lowering of the phospholipid T_c. That is, in the presence of these additives there is observed an apparent dissociation between the phase transition and the permeability maximum. It is proposed that the permeability maximum normally observed in the temperature region of the T_c is associated with the completion of the ‘melting’ process. Hence a compound could cause early ‘melting’ of the bilayer but not change its permeability properties if the temperature at which the ‘melting’ process neared completion was not changed.     

Halothane-induced membrane reorganization monitored by DSC,freeze fracture electron microscopy and 31 P-NMR techniques

The effect of the volatile anaesthetic halothane on the structure and dynamics of lipid multilayers (dimyristoyl- and dipalmitoylphosphatidylcholine, DM-and DP-PC, aqueous dispersions) was studied using Differential Scanning Calorimetry (DSC), Freeze Fracture Electron Microscopy and solid state phosphorus-31 Nuclear Magnetic Resonance (³¹P-NMR). The action of the drug depends upon the halothane-to-lipid molar ratio, Ri, and temperature. With DPPC lipids, three main regions can be distinguished: i) 0 < Ri < 0.7, ii) 0.7 < Ri < 2 and iii) Ri > 2. As Ri increases in the first region, a linear decrease in the main gel-to-fluid phase transition temperature (T _c, a broadening in the DSC transition peak and a lowering in the enthalpy variation (H), are observed. A minimum in H is reached at Ri=0.7. In this region, ³¹P-NMR spectra indicate that the multibilayer structure is maintained. In the second region, T _c still decreases with the same slope, but H increases up to a plateau value for Ri=2. In the lipid fluid phase, an isotropic NMR line appears superimposed on the powder pattern that corresponds to a lamellar phase. For Ri > 2, T _c and H remain almost constant. At values of temperature that are greater than T _c a growing isotropic line occurs in ³¹P-NMR spectra. This means a new supramolecular structure made of lipids and halothane is stabilized. This structure has been characterized as small vesicles of about 400 Å to 600 Å diameter by Freeze Fracture electron microscopy observations. With DMPC and low ratios (Ri < 2), DSC and NMR results are similar to those obtained for DPPC. However, the minimum H is reached at Ri=0.2 and the decrease in T _c is faster than for DPPC when Ri increases from 0. For Ri > 2, while T _c and H remain constant as in the case of DPPC, ³¹P-NMR spectra of DMPC systems show a superimposition of an isotropic line and two powder patterns, which correspond to small tumbling vesicles, a possible hexagonal phase and a lamellar phase respectively. Halothane, thus acts on model membranes in two different steps: at low Ri the bilayer is disturbed but keeps its structure. Whereas for higher drug concentrations, a new organization of lipids seems to be stabilized for T > T _c.Abbreviations DPPC Dipalmitoylphosphatidylcholine - DMPC Dimyristoylphosphatidylcholine - DSC Differential scanning calorimetry - NMR Nuclear magnetic resonance - EDTA Ethylenediaminetetraacetic acid - DMSO Dimethyl sulfoxide - Ri Halothaneto-lipid molar ratio - T _c Main gel (L )-to-fluid (L ) phase transition temperature - T _m Maximum temperature of the transition - H Enthalpy variation - C _{p max} excess heat capacity at the maximum temperature of the transition T _m - n number of phospholipid molecules per cooperative unit Offprint requests to: J.-P. Renou     

Hemoglobin senses body temperature

When aspirating human red blood cells (RBCs) into 1.3 μm pipettes (ΔP = −2.3 kPa), a transition from blocking the pipette below a critical temperature T _c = 36.3 ± 0.3°C to passing it above the T _c occurred (micropipette passage transition). With a 1.1 μm pipette no passage was seen which enabled RBC volume measurements also above T _c. With increasing temperature RBCs lost volume significantly faster below than above a T _c = 36.4 ± 0.7 (volume transition). Colloid osmotic pressure (COP) measurements of RBCs in autologous plasma (25°C ≤ T ≤ 39.5°C) showed a T _c at 37.1 ± 0.2°C above which the COP rapidly decreased (COP transition). In NMR T₁-relaxation time measurements, the T₁ of RBCs in autologous plasma changed from a linear (r = 0.99) increment below T _c = 37 ± 1°C at a rate of 0.023 s/K into zero slope above T _c (RBC T₁ transition). In conclusion: An amorphous hemoglobin–water gel formed in the spherical trail, the residual partial sphere of the aspirated RBC. At T _c, a sudden fluidization of the gel occurs. All changes mentioned above happen at a distinct T _c close to body temperature. The T _c is moved +0.8°C to higher temperatures when a D₂O buffer is used. We suggest a mechanism similar to a “glass transition” or a “colloidal phase transition”. At T _c, the stabilizing Hb bound water molecules reach a threshold number enabling a partial Hb unfolding. Thus, Hb senses body temperature which must be inscribed in the primary structure of hemoglobin and possibly other proteins. This article is dedicated to Ludwig Artmann who died on July 21, 2001 on a beautiful summer day during which we performed experiments far away. Ludwig Artmann was a man who encouraged us to be strong and to study hard no matter what were the costs.     

Adsorption of the polypeptides on a solid surface. III. Behavior of stiff chains in a pore

A strict analytical theory has been developed describing the behavior of a model lattice polymer chain of arbitrary stiffness in a slitlike pore at polymer–adsorbent interaction energies –ε. The thermodynamic characteristics of the system were calculated. It was shown that the transition of the macromolecule from the solution volume inside a pore occurs by the first-order phase transition with evolution of latent heat of adsorption. The transition point –ε = –ε_c is determined by the chain stiffness and is independent of the pore width D. It is shown that in the precritical range, –ε < –ε_c, the free energy ΔF of the macromolecules in the pores is adequately described by the universal dependence ΔF = ΔF(D*/A), where D* is some effective pore width depending on the value of –ε, and A is the length of the Kuhn segment. At high attraction energies, –ε ? –ε_c, the macromolecules are bonded to the pore walls by a great number of units and their free energy depends only on –ε and the chain stiffness, ΔF = ΔF(A, ε). Close to the critical energy –ε ? –ε_c (transition range), ΔF is determined by both the stiffness of the macromolecule and the pore width D: ΔF ～ A²D^?1 for fairly high values of A and D. The possibilities of using porous media as protein stabilizers are discussed, and the value of the stabilizing effect depending on the chain stiffness is estimated.     

Thermodynamics of the first transition in writhe of a small circular DNA by Monte Carlo simulation

Monte Carlo simulations are employed to investigate the thermodynamics of the first transition in writhe of a circular model filament corresponding to a 468 base-pair DNA. Parameters employed in these simulations are the torsional rigidity, C = 2.0 × 10⁻¹⁹ dyne cm², and persistence length, P = 500 Å. Intersubunit interactions are modeled by a screened Coulomb potential. For a straight line of subunits this accurately approximates the nonlinear Poisson-Boltzmann potential of a cylinder with the linear charge density of DNA. Curves of relative free energy vs writhe at fixed linking difference (Δ1) exhibit two minima, one corresponding to slightly writhed circles and one to slightly underwrithed figure-8's, whenever Δ1 lies in the transition region. The free energies of the two minima are equal when Δ1_c = 1.35, which defines the midpoint of the transition. At this midpoint, the free energy barrier between the two minima is found to be ΔG_bar = (0.20) k_BT at 298 K. Curves of mean potential energy vs writhe at fixed linking difference similarly exhibit two minima for Δ1 values in the transition region, and the two minimum mean potential energies are equal when Δ1 = 1.50. At the midpoint writhe, Δ1_c = 1.35, the difference in mean potential energy between the minimum free energy figure-8 and circle states is (1.3) k_BT, and the difference in their entropies is 1.3 k_B. Thus, the entropy of the minimum free energy figure-8 state significantly exceeds that of the circle at the midpoint of the transition. The first transition in writhe is found to occur over a rather broad range of Δ1 values from 0.85 to 1.85. The twist energy parameter (E_T), which governs the overall free energy of supercoiling, undergoes a sigmoidal decrease, while the translational diffusion coefficient undergoes a sigmoidal increase, over this same range. The static structure factor exhibits an increase, which reflects a decrease in radius of gyration associated with the circle to figure-8 transition. © 1996 John Wiley & Sons, Inc.     

On the possibility of true phase transition in heterogeneous DNA during thermal denaturation under conditions close to equal stability of A+T and G+C pairs

The DNA helix–coil transition has been studied in the presence of high concentrations of manganese ions (about 10^?3M), which corresponds to the conditions close to equal stability of the A+T and G+C pairs, at the ionic strengths of 10^?1, 10^?2, and 1.6 × 10^?3M Na⁺. With the Mn²⁺ ion effect, the transition range is significantly reduced to not more than 0.2°C at 1.2 × 10^?3M Mn²⁺ and 1.6 × 10^?3M Na⁺. The melting curves display a sharp kink at the end of the helix–coil transition, which is interpreted as an indication of the second-order phase transition. It is shown that the melting curves obtained can be approximated by a simple analytical expression 1 – θ = exp[–a(t_c - t)], where θ is the DNA helix fraction, t_c is the phase transition temperature, and a is an empirical parameter characterizing the breadth of the melting range and responsible for the magnitude of a jump of the helicity derivative with respect to the temperature at the phase transition point.     

Altererythrobacter flava sp. nov., a new member of the family Erythrobacteraceae,isolated from a surface seawater sample

A Gram-stain-negative, light yellow pigmented, non-motile and aerobic bacterial strain, designated HHU E2-1 ^T, was isolated from a surface seawater sample. The 16S rRNA gene sequence analysis indicated that HHU E2-1 ^T shared the highest sequence similarity to the type strain Qipengyuania gaetbuli DSM 16225 ^T (96.90%), which belongs to the family Erythrobacteraceae. Combined phylogeny of 288 single-copy orthologous gene clusters, analysis of average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH), average amino acid identity (AAI) and evolutionary distances suggested that HHU E2-1 ^T can be considered as a member of the genus Altererythrobacter based on the recently proposed standard for defining genera of Erythrobacteraceae. Strain HHU E2-1 ^T grew at 15–35 °C and pH 5.0–8.0, with optimum growth at 28 °C and pH 7.0. Tolerance to NaCl was up to 4% (w/v) with optimum growth in 2–3% NaCl. The major fatty acids (>?10%) were C_18:1ω7c11-methyl, summed feature 3 (C_16:1ω7c and/or C_16:1ω6c), and summed feature 8 (C_18:1ω7c and/or C_18:1ω6c). The predominant isoprenoid quinone was ubiquinone-10. The genomic G?+?C content was 57.40%. On the basis of the phenotypic, phylogenetic and chemotaxonomic characterizations, HHU E2-1 ^T represents a novel species of the genus Altererythrobacter, for which the name Altererythrobacter flava sp. nov. is proposed. The type strain is HHU E2-1 ^T (=?CGMCC 1.17394 ^T?=?KCTC 72835 ^T?=?MCCC 1K04226^T).

     

Interaction of filipin with dimyristoylphosphatidylcholine membranes studied by 2H-NMR,circular dichroism,electronic absorption and fluorescence

Interaction of the pentene antibiotic filipin with dimyristoylphosphatidylcholine (DMPC) membranes has been monitored by ²H-NMR, circular dichroism (CD), electronic absorption and fluorescence in the temperature range 10° to 60°C. Interaction appears to depend on whether filipin is added before or after membrane formation and also upon the temperature of the system.When filipin is added to preformed DMPC large unilamellar vesicles (LUV), the association constants, as determined by electronic absorption are 39×10³ M ^-1, 15×10³ M ^-1 and 0.6×10³ M ^-1 at 15°, 30° and 50°C, respectively. Under identical conditions, CD spectra of bound filipin exhibit features characteristic of an aggregation over the whole temperature range.When filipin is incorporated in membranes during their preparation, the ²H-NMR spectra of deuterated DMPC indicate that the drug has a slight disordering effect on the lipid matrix below the temperature, T _c ,of the gel-to-fluid phase transition and above T _c +11°C. Between these two temperature boundaries the system consists of two lipid regions of very different dynamic properties. One of the regions, which is attributed to a filipin-lipid complex, has the properties of gel-like lipids whereas the other has those of fluid-like lipids. The latter domain is however more ordered than the pure lipid at corresponding temperatures. CD spectra under the same conditions are found to be identical to spectra when the drug is added to preformed membranes, only in the region T _c to T _c +11°C.Filipin induced carboxyfluorescein release from DMPC-LUV is found to be complete when the filipin-to-lipid ratio is near 1, for temperatures below T _c +11°C.Results are compared to previous data on amphotericin B and provide evidence that the gel-like structure of phospholipid and membrane permeation may be induced by filipin even in the absence of cholesterol.Abbreviations NMR nuclear magnetic resonance - CD circular dichroism - DMPC dimyristoylphosphatidylcholine - EPA egg phosphatidic acid - LUV large unilamelar vesicles - SPC soybean phosphatidylcholine - DMSO dimethylsulfoxide - CF carboxyfluorescein     

Enthalpy changes in the helix-coil transition of poly(gamma-benzyl L-glutamate)

The helix-coil transition temperature T_c of poly(γ-benzyl L -glutamate) in binary solvent mixtures of dichloroacetic acid and 1,4-dichlorobutane, 1-chlorooctane, or 1-chlorododecane have been measured. A treatment is presented with which the transition enthalpy can be calculated from the observed dependence of T_c on solvent composition. Results are compared with previously obtained calorimetric data. The underlying assumptions of the calculation are discussed.     

Pigmentiphaga soli sp. nov., a bacterium isolated from soil

Strain BS12^T, a Gram-negative motile bacterium, was isolated from soil in South Korea and characterized to determine its taxonomic position. Phylogenetic analyses based on the 16S rRNA gene sequence revealed that the strain belonged to the family Alcaligenaceae in the class Betaproteobacteria. The highest degree of sequence similarities of strain BS12^T were found with Pigmentiphaga litoralis JSM 061001^T (98.3%), Pigmentiphaga daeguensis K110^T (98.2%), and Pigmentiphaga kullae K24^T (98.1%). Chemotaxonomic data revealed that strain BS12^T possessed ubiquinone-8, which is common in the family Alcaligenaceae, and the predominant fatty acids were C_16:0, C_17:0 cyclo, summed feature 3 (C_16:1 ω6c/ω7c), and summed feature 8 (C_18:1 ω6c/ω7c). The major polar lipids of strain BS12^T were phosphatidylethanolamine and phosphatidylglycerol. Based on these data, BS12^T (=KCTC 23577^T =JCM 17666^T =KEMB 9004-082^T) should be classified as a type strain of a novel species, for which the name Pigmentiphaga soli sp. nov. is proposed.     

Lectin-mediated agglutination of liposomes containing glycophorin: Effects of acyl chain length

Glycophorin from human erythrocytes has been incorporated into liposomes of dimyristoylphosphatidylcholine (DMPC), dipalmitoylphosphatidylcholine (DPPC) and distearoylphosphatidylcholine (DSPC). The thermal properties of unsonicated liposomes with glycophorin/lipid molar ratios up to 4·10^?3 have been studied by differential scanning calorimetry and the numbers of lipids withdrawn from participation in the gel-to-lamellar phase transition were found to be 42±22 (DMPC), 197±28 (DPPC) and 240±64 (DSPC). The initial rates of agglutination of sonicated liposomes with glycophorin/lipid molar ratios up to 4·10^?3 by wheat germ agglutinin in the concentration range 0–7 μM have been measured over a range of temperature. Below the gel-to-lamellar phase transition (T_c) the rates of agglutination increase with acyl chain length in the sequence DMPC < DPPC < DSPC. Agglutination is found to be second order in liposome concentration and is completely reversed on saturation of the wheat germ agglutinin-binding sites by N-acetylglucosamine. Agglutination rates decrease with increasing temperature below T_c and are largely independent of temperature above T_c. The results are discussed in relation to the clustering of glycophorin in the phospholipid bilayers and its effect on binding and subsequent interliposomal bridge formation by wheat germ agglutinin.     

<Emphasis Type="Italic">Panacagrimonas perspica</Emphasis> gen. nov., sp. nov., a novel member of <Emphasis Type="Italic">Gammaproteobacteria</Emphasis> isolated from soil of a ginseng field

A taxonomic study was carried out on Gsoil 142^T, a bacterial strain isolated from the soil collected in a ginseng field in Pocheon province, South Korea. Comparative 16S rRNA gene sequence studies showed a clear affiliation of this bacterium to the Gammaproteobacteria, and it was most closely related to Hydrocarboniphaga effusa ATCC BAA 332^T (94.4%, 16S rRNA gene sequence similarity), Nevskia ramosa DSM 11499^T (94.1%) and Alkanibacter difficilis MN154.3^T (92.0%). Strain Gsoil 142^T was a Gram-negative, strictly aerobic, motile, and rod-shaped bacterium. The G+C content of the genomic DNA was 69.9% and predominant ubiquinone was Q-8. Major fatty acids were summed feature 8 (C_18:1 ω7c and/or ω6c, 36.3%), summed feature 3 (iso-C_15:0 2-OH and/or C_16:1 ω7c, 20.6%) and C_16:0 (17.4%). The major polar lipids detected in strain Gsoil 142^T were phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, and an unknown glycolipid. On the basis of polyphasic evidence, it is proposed that strain Gsoil 142^T should be placed in a novel genus and species, for which the name Panacagrimonas perspica gen. nov., sp. nov. is proposed. The type strain is Gsoil 142^T (= KCTC 12982^T = LMG 23239^T).     

Functional group contributions to the partitioning of phenols between liposomes and water

The temperature dependency of the partitioning of p-alkylphenols and p-halophenols has been determined between dimyristoyl phosphatidylcholine liposomes and 0.15 M NaCl. Partition coefficients increased as a function of temperature below the endothermic phase transition temperature (T_c) of the phospholipid but decreased above this temperature. The transfer process was found to be entropy-dominated below and enthalpy-dominated above the T_c, although large negative entropy changes were observed. Regular changes in the thermodynamic functions, partition coefficients and functional group free energies occurred as a function of the alkyl chain length or size of the halogen substituent below but not above the T_c. This has tentatively been attributed to increased phenol-phospholipid interaction at the higher temperatures. The partitioning of p-fluorophenol behaved in a manner expected of fluorinated compounds, yielding relatively low partition coefficients, but it produced an additional effect of markedly lowering the T_c of dimyristoyl phosphatidylcholine. Good correlations of the partition coefficients in liposomes with those in bulk organic solvents and with molecular size of the solute have been obtained.     

Dynamic properties of the backbone of an integral membrane polypeptide measured by 2H-NMR

The ²H-NMR spectrum of the exchangeable hydrogens of the synthetic amphiphilic polypeptide, lys₂-gly-leu₂₄-lys₂-ala-amide, was measured for the solid peptide at room temperature and, as a function of temperature, for the peptide incorporated into hydrated dipalmitoylphosphatidylcholine (DPPC) bilayers. This study is a prototype of a similar class of experiments which can be carried out on integral membrane proteins to characterize, quantitatively, the dynamic properties of integral membrane proteins. At temperatures below the DPPC gel-liquid crystalline phase transition, the ²H NMR spectrum was very similar to that of the solid peptide indicating that the peptide was immobilized in the lipid bilayer on the time scale (10^-5 s) of the ²H-NMR measurements. The ²H-NMR spectrum above the phase transition corresponded to that expected from a peptide in the -helical conformation reorienting rapidly about the symmetry axis of the -helix. Measurements of the quadrupolar echo relaxation time, T _2e , gave a quantitative measure of the correlation time, _c , for this motion. The value of _c decreased rapidly with increasing temperature as the fraction of DPPC molecules in the liquid crystalline phase increased, reaching a value of 2×10^-7s above the phase transition. The observation of a characteristic minimum in T _2e as the temperature was raised provided a definitive, quantitative interpretation of the T _2e measurements. Using the known geometry of the peptide and the theory of uniaxial rotational diffusion, a value of =1.1 poise was obtained for the effective viscosity of the membrane in close agreement with values obtained previously from transient linear dichroism measurements.Abbreviations NMR nuclear magnetic resonance - DPPC dipalmitoylphosphatidylcholine - K₂GL₂₄K₂A-amide lys₂-gly-leu₂₄-lys₂-ala-amide     

Adsorption of Carbon Dioxide to Polysaccharides in the Supercritical Region

The adsorption isotherms for C0₂ to several polysaccharides were measured in a pressure range between 0 and 29.4 MPa by the gravimetric method. The adsorption of C0₂ to two kinds of starches (potato and corn) and to dextrin increased linearly with increasing pressure to reach a maximum, and then decreased sharply to constant level at higher pressure. These adsorption characteristics are similar to those of proteins reported previously. On the other hand, the adsorption of C0₂ to cellulose showed a high level at the beginning of the increase in pressure, without any significant change in the sub-critical pressure region, and then fell to the minimum before reaching a constant level at higher pressures. These adsorption characteristics of cellulose could be related to its micropore structure. The pressure at which the maximum adsorption occurred (P_max) was located on the P-T line of the C0₂ phase diagram where (dpfdP)_T was a maximum, this result being different from the Menon correlation of P_max = P_c(T/T_c)² proposed for adsorption to macroporous adsorbents.