Thermotropic behavior of major phospholipids from marine invertebrates: changes with warm-acclimation and seasonal acclimatization

The crystal-liquid crystal-isotropic melt phase transitions of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) from muscle tissue of five species (actinia Metridium senile fimbriatum, mussel Crenomytilus grayanus, sea-urchin Strongylocentrotus intermedius, starfish Distolasterias nipon and the ascidian Halocynthia aurantium) of marine invertebrates, collected in winter at 0 degrees C and then acclimated to 18.5 degrees C for 5 days, were studied by differential scanning calorimetry and polarising microscopy. To elevate temperature from 0 to 18.5 degrees C, we used the rate of 4.5 degrees C/h. Although phase transitions of both phospholipids from animals collected in summer occurred already at temperatures below -1.7 oC (minimal temperature of seawater in winter), compensatory mechanisms resulted in a decrease by 29-43 oC in the phase transition temperature of PE in winter. Thermotropic behavior of PCs changed in various trends. However, the total heat of their phase transitions always decreased in winter compared with summer. For all species, except the mussel, the time of warm-acclimation was insufficient to adjust the thermotropic behavior of either phospholipid. Nevertheless, the unsaturation index decreased to achieve summer values, due primarily to decreased proportions of eicosapentaenate and docosahexaenate. The accumulation of arachidonate, during warm-acclimation, might be connected to the signalling properties of n-6 eicosanoids. Absence of effective homeoviscous mechanisms suggests that most of the studied marine invertebrates have very limited capacity to survive an acute temperature elevation, e.g. at the appearance of thermal currents.     

Seasonal changes of fatty acid composition and thermotropic behavior of polar lipids from marine macrophytes

Major glyco- and phospholipids as well as betaine lipid 1,2-diacylglycero-O-4'-(N,N,N-tri-methyl)-homoserine (DGTS) were isolated from five species of marine macrophytes harvested in the Sea of Japan in summer and winter at seawater temperatures of 20-23 and 3 degrees C, respectively. GC and DSC analysis of lipids revealed a common increase of ratio between n-3 and n-6 polyunsaturated fatty acids (PUFAs) of polar lipids from summer to winter despite their chemotaxonomically different fatty acid (FA) composition. Especially, high level of different n-3 PUFAs was observed in galactolipids in winter. However, the rise in FA unsaturation did not result in the lowering of peak maximum temperature of phase transition of photosynthetic lipids (glycolipids and phosphatidylglycerol (PG)) in contrast to non-photosynthetic ones [phosphatidylcholine (PC) and phosphatidylethanolamine (PE)]. Different thermotropic behavior of these lipid groups was accompanied by higher content of n-6 PUFAs from the sum of n-6 and n-3 PUFAs in PC and PE compared with glycolipids and PG in both seasons. Seasonal changes of DSC transitions and FA composition of DGTS studied for the first time were similar to PC and PE. Thermograms of all polar lipids were characterized by complex profiles and located in a wide temperature range between -130 and 80 degrees C, while the most evident phase separation occurred in PGs in both seasons. Polarizing microscopy combined with DSC has shown that the liquid crystal - isotropic melt transitions of polar lipids from marine macrophytes began from 10 to 30 degrees C mostly, which can cause the thermal sensitivity of plants to superoptimal temperatures in their environment.     

Seasonal changes of phospholipids in last instar larvae of rice stem borer Chilo suppressalis Walker (Lepidoptera: Pyralidae)

Phospholipids of the cell membrane have been studied from the viewpoint of how overwintering insects inhabiting temperate zones adapt to low temperature. The transition of cell membrane phospholipids from a liquid crystalline phase to a gel phase is a crucial cause of cold or freezing injuries. We determined the qualitative and quantitative changes of phospholipids in the last instar larvae of the rice stem borer in summer and winter. We found that the total amount of their phospholipids did not change significantly between summer and winter and that the sum of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) comprised about 85% of their total phospholipids. In summer, the ratio of their PE to PC was almost one, while from autumn to mid‐winter it increased and reached three in February. The fatty acid compositions of PC hardly changed, and the percentage of unsaturated fatty acids did not exceed 50%. In contrast, the percentage of unsaturated fatty acids of PE in overwintering larvae increased up to 80% as ambient temperatures fell and oleic acid mainly contributed to the high percentage of unsaturation. In the present study, the relationship between the quantitative and qualitative changes of phospholipids and adaptation of the rice stem borer to cold winter climate are discussed.     

Effects of zinc on lipids of erythrocytes from carp (Cyprinus carpio L.) acclimated to different temperatures

We compared the effect of zinc (0.01, 0.1, 0.5 and 1 mM) at two temperatures (5 and 20 degrees C) on erythrocytes from summer and winter acclimatised carp. An increase in temperature from 5 to 20 degrees C increased the unsaturation index (UI) and relative proportion (UI/SFA) of unsaturated to saturated fatty acids in total lipids of the red cells. At 5 degrees C, the unsaturation index of phosphatidylcholine (PC), phosphatidylserine (PS), phosphatidylethanolamine (PE) and phosphatidylinositol (PI) decreased (30-40%) in the presence of 1 mM zinc. The change in unsaturation of phospholipids in the presence of zinc at 5 degrees C is probably responsible for the alteration in structural integrity of erythrocyte membrane as observed by hemolysis and the decreased thiol group content in the erythrocytes. In light of this result, zinc may be considered an environmental hazard for these fish at low temperatures.     

The thermotropic behavior and fatty radical composition of major phospholipids of the tanner crab <Emphasis Type="Italic">Chionoecetes bairdi</Emphasis> Rathbun, 1924

This study examines the fatty radical (FR) composition and heat-induced crystalline to liquidcrystalline phase transitions of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) from the gills, hepatopancreas, gonads, and muscle of the tanner crab Chionoecetes bairdi, which was collected in the summer at a near-bottom water temperature of 2.8°C. The location of the PC and PE thermograms below 2.8°C indicates the functionally optimal liquid crystalline state of the membrane lipid matrix. The proximity of the thermogram profiles of PC and PE from the different organs and tissues of C. bairdi and significant overlapping of the temperature areas of transitions (symbatic behavior) correlate with a similar composition of major FR and their total parameters in PC and PE. The obtained data point to the effective adaptation of the bairdi crab to low water temperatures and to the need for adaptive changes in the FR composition or change of habitat with increasing temperature. The thermotropic behavior of muscle PC, in which the greater part of the thermogram is in the temperature range from 2.8 to 32°C, suggests a potential for the tanner crab to adapt to increased temperatures.     

Temperature-induced alterations in phospholipids of Fusarium oxysporum f. sp. lycopersici.

Ten phospholipids were identified in hyphal membrane preparations of Fusarium oxysporum f. sp. lycopersici when the cells were grown to the late log phase at 15, 25, and 37 degrees C, respectively. The major phospholipids present were phosphatidylcholine (PC) and phosphatidylethanolamine (PE), which together made up about 70% of the total membrane phospholipids. The degree of unsaturation in the acyl group of the phospholipids was inversely related to growth temperature. The polar head group composition was also affected by growth temperature. Cells grown at 15 and 25 degrees C contained the same relative proportions of PC and PE, but when the growth temperature was raised to 37 degrees C, the ratio of PC to PE was doubled. A methylating system capable of converting PE to PC was demonstrated in vitro.     

Thermotropic properties of saturated mixed acyl phosphatidylethanolamines

The mixed acyl phosphatidylethanolamine (PE) series C(18)C(18)PE, C(18)C(16)PE, C(18)C(14)PE, C(18)C(12)PE, and C(18)C(10)PE has been prepared from the corresponding phosphatidylcholines by phospholipase D mediated transphosphatidylation. The thermotropic behavior of unhydrated and hydrated preparations of these PEs has been investigated by differential scanning calorimetry and 31P NMR spectroscopy. Unhydrated preparations of the PEs undergo crystalline to liquid-crystalline transitions (Tm+h), which correspond to the simultaneous hydration and acyl chain melting of poorly hydrated crystalline samples. Hydrated preparations of the PEs undergo gel to liquid-crystalline transitions (Tm) when scanned immediately subsequent to cooling from temperatures above their respective Tm+hs. Multilamellar bilayers of C(18)C(18)PE, C(18)C(16)PE, and C(18)C(14)PE pack without significant interdigitation of the phospholipid acyl chains across the bilayer center in the gel phase. C(18)C(10)PE multilamellar preparations exhibit a mixed-interdigitated gel phase packing of the phospholipid acyl chains. Hydrated bilayers of C(18)C(12)PE adopt a mixed-interdigitated gel phase packing at temperatures below 13.9 degrees C. Between 13.9 degrees C and the gel to liquid-crystalline transition temperature of 36.9 degrees C, the C(18)C(12)PE bilayer adopts a noninterdigitated gel phase packing. The metastable behavior of fully hydrated and partially hydrated preparations of the mixed acyl PEs has been investigated. Bilayers of C(18)C(18)PE, C(18)C(16)PE, and C(18)C(14)PE exhibited little or no tendency toward regeneration of the crystalline phase. In contrast, bilayers of C(18C(12)PE and C(18)C(10)PE exhibited a metastability of the liquid-crystalline phase in the temperature interval between Tm and Tm+h, which can allow for the regeneration of the crystalline phase under certain conditions.Bilayers of C(18)C(12)PE exhibited an additional metastability of the noninterdigitated gel phase.     

Thermotropic behavior of retinal rod membranes and dispersions of extracted phospholipids

Summary High sensitivity, differential scanning calorimetry studies of vovine retinal rod outer segment (ROS) disk membranes and aqueous dispersions of the extracted ROS phospholipids have been performed. ROS disk membranes were found to exhibit a broad peak of excess heat capacity with a maximum at less than about 3°C, ascribable to a gel-to-liquid crystalline phase transition of traction of the phospholipids. A similar thermotropic transition was observed for aqueous dispersions of the total extracted and purified ROS phospholipids. Comparison of the results obtained for the dispersion of total ROS phospholipids to those of the purified head group fractions. suggests that the thermotropic behavior reffects a gel-to-liquid crystalline transition, leading to lateral phase separation, involving those phosphatidylcholine (PC) molecules containing saturated fatty acylchains, possibley together with the highest melting ROS phosphatidylethanolamine (PE) and phosphatidylserine (PS) components. The interpretation of the thermal behavior of the ROS disk membranes depends on whether the transition is assumed to derive from the ROS PC and/or PE/PS fractions, and whether the transbilayer arrangement of the ROS phospholipids is assumed to be symmetric or asymmetric. The calorimetric data can be simply explained in terms of an asymmetric distribution of the major ROS disk membrane phospholipids (G.P. Miljanich et al.,J. Membrane Biol. 60:249–255, 1981). In this case, the transition would arise from the PE/PS fractions in the outer ROS disk membrane monolyer, and the anticipated transition from the PC in the inner monolayer would be broadened due to interaction with cholesterol. For the ROS membranes at higher temperatures, two additional, irreversible transitions are observed at 57 and 72°C, corresponding to the thermal denauturation of opsin and rhodopsin, respectively.     

The incorporation of unsaturated fatty acids of the n-9, n-6, and n-3 families into individual phospholipids by isolated hepatocytes of thermally-acclimated rainbow trout, Salmo gairdneri

Rates of incorporation of 1-14C-oleic (18:1n9), -linoleic (18:2n6), and -linolenic (18:3n3) acids into individual phosphatides were determined in isolated hepatocytes from cold (5 degrees C)- and warm (20 degrees C)-acclimated rainbow trout, Salmo gairdneri. Fatty acid incorporation into phosphatidylcholine (PC) exceeded that into all other phospholipids, but at assay and acclimation temperatures of 5 degrees C, incorporation into phosphatidylethanolamine (PE) was generally intermediate between that of PC and the remaining phosphatides. Specific radioactivities (ratios of percentage isotope incorporation-to-mole percentage of phosphatide) were consistently less than one for both PC and PE, and greater than one for phosphatidic acid (PA), lysophosphatidylcholine (LPC), phosphatidylserine (PS), and cardiolipin (CL). For PS, specific radioactivities were greater in cold- than warm-acclimated trout, and greater at 5 degrees C than 20 degrees C. Rates of oleate incorporation were generally higher, and rates of incorporation of 18:2 and 18:3 lower in cold- than warm-acclimated trout. Most phospholipids demonstrated a clear preference for the incorporation of 18:2 when assayed at 20 degrees C; however, at 5 degrees C the incorporation of 18:2 was reduced and 18:3 was generally the preferred substrate. A reduction in assay temperature from 20 degrees C to 5 degrees C also shifted the incorporation of 18:2 away from PC into PS and PA. These data were interpreted to indicate 1) a cold-induced activation of PS metabolism, possibly resulting in elevated levels of PE; 2) lower rates of general acyl group turnover in animals acclimated to 5 degrees C than 20 degrees C; 3) a specificity to the acclimation response that favors the incorporation at cold temperatures of polyunsaturated fatty acids, but not the parent acids from which they are derived; and 4) the participation of a deacylation-reacylation cycle in the metabolism of phospholipids, particularly at cold temperatures.     

Solid- and liquid-phase equilibria in phosphatidylcholine/phosphatidylethanolamine mixtures. A calorimetric study

Phase diagrams have been determined for mixing of binary mixtures of phosphatidylethanolamines (PE) with phosphatidylcholines (PC), using high-sensitivity differential scanning calorimetry and allowing extensive incubation times to equilibrate samples in the solid phase. All of the PE-PC systems examined, which contained saturated or trans-unsaturated PC components, showed limited solid-phase miscibility, chiefly because the PC component can adopt more solid phases than the PE component. For the dielaidoyl PE-PC system, the lamellar-to-hexagonal II transition endotherm seen at 63.5 degrees C for the pure PE is shifted to considerably higher temperatures upon incorporation of even low mole fractions of PC. All of the PE-PC systems examined here reveal a complete miscibility in the liquid phase, including the dipalmitoyl PE-dielaidoyl PC system for which limited liquid-phase miscibility had previously been suggested (Wu, S-H. and McConnell, H.M. (1975) Biochemistry 14, 847-854). However, PE-PC mixing appears to be less nearly ideal than the mixing of either PE or PC with anionic phospholipids. Our results demonstrate that calorimetry can be useful in determining accurate phase diagrams for lipid mixtures of this type, but only if proper attention is given to the existence and the proper equilibration of multiple solid phases in these systems.     

Thermodynamic and phase characterization of phosphatidylethanolamine and ganglioside GD1a mixtures

By employing diphenylhexatriene steady-state fluorescence anisotropy, pyrenedecanoic acid excimer formation, and high sensitivity scanning calorimetry we have demonstrated that the liposomes containing phosphatidylethanolamine (PE) and various mole fractions of ganglioside GD1a had a gel-liquid crystalline phase transition between 15 and 25 degrees C. Calorimetric measurements indicated that these phase transitions were broad and centered between 17 and 21 degrees C. The enthalpy change of the transition was linearly dependent on the ganglioside concentration up to 10.0 mol% and plateaued between 11.4-16.2 mol%. The high enthalpy change (37 kcal/mol of GD1a added into the PE bilayer) indicates the existence of PE-GD1a complex structure in the liposomal membrane. It is proposed that semi-fluid domains containing six PE and one ganglioside molecule are present in the PE-GD1a membranes at temperatures above gel-liquid crystalline phase transition. The Sendai virus induced leakage of PE-GD1a liposomes has been investigated by using an entrapped, self-quenching fluorescent dye, calcein. The leakage rate was dependent on the mole fraction of ganglioside GD1a and was maximal at 6.3 mol%. Arrhenius plots of the leakage rates showed breaks in the 20-25 degrees C temperature range, which correspond to the gel-liquid crystalline phase transition of the target liposomes. These data suggest that the rate of Sendai virus-induced leakage can be regulated via fluidity modulation by changing the PE to GD1a ratio at constant temperatures.     

Infrared and time-resolved fluorescence spectroscopic studies of the polymorphic phase behavior of phosphatidylethanolamine/diacylglycerol lipid mixtures

Fourier transform infrared (FTIR) and time-resolved fluorescence spectroscopy have been employed to examine the structural dynamics of lipid fatty acyl chains and lipid/water interfacial region of a binary lipid mixture containing unsaturated phosphatidylethanolamine (PE) and diacylglycerol (DG). Infrared vibrational frequencies of the CH2 symmetric stretching and the C = O stretching bands of the lipids were measured at different lipid compositions and temperatures. For 0% DG, the lamellar gel to lamellar liquid crystalline (L beta-L alpha) and the L alpha to inverted hexagonal (L alpha-HII) phase transitions were observed at approximately 15 degrees and 55 degrees C, respectively. As the DG content increased gradually from 0% to 15%, the L alpha-HII phase transition temperature decreased drastically while the L beta-L alpha phase transition temperature decreased only slightly. At 10% DG, a merge of these two phase transitions was noticed at approximately 10 degrees C. For the composition study at 23 degrees C, the L alpha-HII transition occurred at approximately 6-10% DG as indicated by abrupt increases in both the CH2 and C = O stretching frequencies at those DG contents. Using time-resolved fluorescence spectroscopy, abrupt decreases in both the normalized long time residual and the initial slope of the anisotropy decay function of lipid probes, 1-palmitoyl-2-[[2-[4-(6-phenyl-trans-1,3,5- hexatrienyl)phenyl]ethyl]carbonyl]-3-sn-phosphatidylcholine, in these PE/DG mixtures were observed at the L alpha-HII phase transition. These changes in the anisotropy decay parameters suggested that the rotational dynamics and orientational packing of the lipids were altered at the composition-induced L alpha-HII transition, and agreed with a previous temperature-induced L alpha-HII transition study on pure unsaturated PE (Cheng (1989) Biophys. J. 55, 1025-1031). The fluorescence lifetime of water soluble probes, 8,1-anilinonapthalenes sulfonate acid, in PE/DG mixtures increased abruptly at the L alpha-HII phase transition, suggesting that the conformation and hydration of the lipid/water interfacial region also undergo significant changes at the L alpha-HII transition.     

Phosphatidylcholine-cholesterol interactions: bilayers of heteroacid lipids containing linoleate lose calorimetric transitions at low cholesterol concentration

Model membranes composed of cholesterol plus one of two phosphatidylcholines (PC), each containing a saturated and a dienoic acyl chain, have been studied by differential scanning calorimetry. The gel to liquid-crystalline phase transition temperature of 1-palmitoyl-2-linoleoyl PC was -19.5 degrees C and that of 1-stearoyl-2-linoleoyl PC was -13.7 degrees C. The addition of cholesterol to the phosphatidylcholines in aqueous dispersion resulted in the progressive removal of the phase transition as observed by differential scanning calorimetry. Per mole of sterol in the membrane, cholesterol was more effective at reducing the enthalpy change of the phase transitions of these bilayers containing dienoic phosphatidylcholines than it is in eliminating the transition of membranes made with other phospholipids that contain more saturated chains. No transitions in membranes made with palmitoyl-linoleoyl PC or stearoyl-linoleoyl PC could be detected calorimetrically when 17 mol% cholesterol was present.     

Effects of replacement of a double bond by a cyclopropane ring in phosphatidylethanolamines: a 2H NMR study of phase transitions and molecular organization

The thermotropic behavior and molecular properties of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) and 1-palmitoyl-2-dihydrosterculoyl-sn-glycero-3-phosphoethanolamine (PDSPE) have been investigated by 2H NMR spectroscopy using samples selectively labeled at the 5'-, 9'-, 10'-, and 16'-positions of the sn-2 chains. Comparison with the corresponding phosphocholine analogues (POPC and PDSPC), obtained as intermediate synthetic products, was used to monitor the role of the polar head group. Replacement of the choline moiety by ethanolamine increased the gel to liquid-crystal transition temperature by 10-32 degrees C and led to a significantly higher ordering of the fatty acyl chains in the liquid-crystalline bilayer state. The lateral compression effect, due to the smaller area per polar head group in PE, results in a bilayer to hexagonal phase transition at elevated temperatures. The effects on both PC and PE due to replacement of the olefinic group by a cyclopropane unit are similar. A decrease in the temperature of the gel to liquid-crystal phase transition, Tc, is observed upon introduction of a cyclopropane ring; it goes from 26 degrees C in POPE to approximately 10 degrees C in PDSPE. In addition, a very significant broadening of the transition profile is observed. These observations are consistent with the poor packing ability of mixed saturated and cyclopropane-containing chains due to the bulky substituent effect. The temperature of the bilayer-hexagonal phase transition of PE samples was decreased by 15-20 degrees C on replacement of oleoyl chains by dihydrosterculoyl chains at the sn-2 position.(ABSTRACT TRUNCATED AT 250 WORDS)     

Transport mechanisms in chloride channels.

A comparative study of lipids and proteins in sarcoplasmic reticulum (SR) from rabbit and flounder has been undertaken. The protein/phospholipid ratio (w/w) was 3:1 in flounder SR (FSR) and 2.2:1 in rabbit SR (RSR). Both membranes had similar contents of PC (70%) and PI (6%). PE constituted 15% in RSR and 21% in FSR. PS and sphingomyelin were minor components of both SR (less than 4%). There were differences in the unsaturated chains of the total lipid extracts, PC, PE, and PI between FSR and RSR. RSR was high in linoleate and arachidonate while FSR contained substantial amounts of eicosapentaenoate and docosahexaenoate. FTIR spectroscopy revealed that the lipids of both membranes did not undergo a phase transition between 0 and 50 degrees C. The lipids were in the liquid-crystalline state at physiological temperatures and underwent monotonic increases in conformational disorder as the temperature was raised. CD spectra indicated higher content of alpha-helical structure of proteins in RSR than in FSR. Increasing temperature caused diminution of alpha-helix content. Relatively large decreases in ellipticity were observed between 20 degrees C and 40 degrees C for FSR and 30 degrees C and 60 degrees C for RSR. Measurements of intrinsic tryptophan fluorescence as a function of temperature gave similar results for membrane proteins in both FSR and RSR. The rate of change of tryptophan fluorescence and fluorescence lifetimes was constant over the temperature ranges studied, and no abrupt shifts in fluorescence occurred in the temperature regions where ellipticity decreased rapidly.     

Differential scanning calorimeter analyses of membrane lipids isolated from hardened and unhardened black locust bark and from winter rye seedlings

Phospholipids isolated from hardened and unhardened cells of the living bark of the black locust tree and from the cells of winter rye seedlings were analyzed by differential scanning calorimetry. In accord with previously reported data which showed little differences in the fatty acid unsaturation of phospholipids obtained from unhardy summer and very hardy winter bark of the black locust, only small differences were found in the temperature and enthalpies of the liquid-crystalline gel phase transitions of the isolated phospholipids of these respective tissues. In the case of winter rye, where fatty acid unsaturation was observed to increase with hardening, the differences in phase transition properties of the phospholipids isolated from hardened and unhardy rye also were found to be minor. In any event, the transition temperatures of the rye phospholipids were well above and that of the locust phospholipids far above the freeze-killing temperatures for these tissues. These results would suggest that both unsaturation and bulk fluidity of the isolated lipids from these plants bear little relationship to their degree of freezing tolerance.     

Phase separations in membranes of Anacystis nidulans grown at different temperatures.

Freeze fracture electron microscopy studies were performed on samples of Anacystis nidulans quenched from different temperatures. Membrane lipid phase separations were observed to take place over the ranges 15--30 degrees C, 5--25 degrees C and -5--15 degrees C for cultures grown at 38, 28 and 18 degrees C, respectively. Differential scanning calorimetry heating curves showed endotherms which coincided with these temperature ranges. Variations of phase separation temperatures with growth temperature, and hysteresis effects in the calorimetric measurements, were related to changes in the fatty acid composition of membrane lipids.     

1954—2005年中国北方针叶林分布区的气候变化特征

基于中国北方针叶林(兴安落叶松林)分布区8个气象观测站的气象资料,分析了1954—2005年气温和降水的变化特征.结果表明：研究期间,中国北方针叶林分布区的气温以0.38 ℃·(10 a)^-1的速度上升,远大于全球近50年来0.13 ℃·(10 a)^-1的平均增温速率.尽管夏、秋季的气温呈上升趋势,但不显著;而冬、春季的增温显著(P<0.01);最高年平均气温(0.37 ℃·(10 a)^-1)与最低年平均气温(0.54 ℃·(10 a)^-1)均呈极显著的增加趋势(P<0.01).降水量年际间波动较大,但没有明显的变化趋势;各季节降水量也没有明显的变化规律,其中春、秋、冬季的降水日数有增加趋势,但没有达到显著水平,而夏季的降水日数呈显著减少趋势(P<0.05);各季降水强度均呈增加趋势,其中夏季(P<0.05)和冬季(P<0.01)的变化达到了显著水平.     

Phase transitions of phospholipids as a criterion for assessing the capacity for thermal adaptation in fish

This study examines the crystal-liquid crystal phase transitions of the major phospholipids, phosphatidylcholine (PC) and phosphatidylethanolamine (PE), from muscle tissue of marine fish living at temperatures of 0–4.1°C (the Pacific cod Gadus macrocephalus, banded Irish lord Hemilepidotus gilberti, Pacific halibut Hippoglossus hippoglossus, black edged sculpin Gymnocanthus herzensteini, dark colored flounder Pleuronectes obscurus, and plain sculpin Myoxocephalus jaok), as well as of fish living at 14 and 18°C (Pacific redfin Tribolodon brandti). The PC and PE phase-transition thermograms of all the investigated species displayed specific profiles. The largest share of the thermogram area at temperatures higher than those of the habitat was found for the PC (28–40%) and PE (47–82%) of the black-edged sculpin, dark-colored flounder, and the plain sculpin, which have reduced physiological activity at low temperatures. In the Pacific cod, banded Irish lord, and the Pacific redfin, this parameter was much lower, 0–18% (PC) and 0–39% (PE). The thermotropic behavior PC and PE was symbate in all fish, except for the cod and the plain sculpin. The transition enthalpy of PC in all the investigated species was 2.8 times higher than that of PE. To interpret the varied PC and PE thermogram profiles of fish with similar fatty-acid compositions, the data on the composition of the molecular species of these phospholipids appeared to be the most informative. This study suggests that each fish species has its own strategy for thermal adaptation, which is realized through a certain set of phospholipid molecular species.     

Phase transitions as a function of osmotic pressure in Saccharomyces cerevisiae whole cells, membrane extracts and phospholipid mixtures

Fourier Transform Infrared spectroscopy (FTIR) was used to determine the phase transition temperature of whole Saccharomyces cerevisiae W303-1 A cells as a function of Aw in binary water-glycerol media. A phase transition occurred at 12 degrees C in water, at 16.5 degrees C at Aw=0.75, and at 19.5 degrees C at Aw=0.65. The temperature ranges over which transition occurred increased with decreasing Aw. A total lipid extract of the plasma membranes isolated from S. cerevisiae cells was also studied, with a phase transition temperature determined at 20 degrees C in pure water and at 27 degrees C in binary water-glycerol solutions for both Aw levels tested. The pure phospholipids dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE) and three binary mixtures of these phospholipids (percentage molar mixtures of DMPC/DMPE of 90.5/9.5, 74.8/25.2, and 39.7/60.3) were studied. For DMPC, there was no influence of Aw on the phase transition temperature (always 23 degrees C). On the other hand, the phase transition temperature of DMPE increased with decreasing Aw for the three aqueous solutions tested (glycerol, sorbitol and sucrose), from 48 degrees C in water, to 64 degrees C for a solution at Aw=0.67. For the DMPC/DMPE mixtures, transitions were found intermediate between those of the two phospholipids, and a cooperative state was observed between species at the gel and at the fluid phases.