Temperature change of the ripple structure in fully hydrated dimyristoylphosphatidylcholine/cholesterol multibilayers.

The ripple structure was studied as a function of temperature in fully hydrated dimyristoylphosphatidylcholine (DMPC)/cholesterol multibilayers using synchrotron x-ray small-angle diffraction and freeze-fracture electron microscopy. In the presence of cholesterol, the ripple structure appears below the pretransition temperature of pure DMPC multibilayers. In this temperature range the ripple periodicity is relatively large (25-30 nm) and rapidly decreases with increasing temperature. In this region, defined as region I, we observed coexistence of the P beta' phase and the L beta' phase. The large ripple periodicity is caused by the formation of the P beta' phase region in which cholesterol is concentrated and the L beta' phase region from which cholesterol is excluded. An increase in ripple periodicity also takes place in the narrow temperature range just below the main transition temperature. We define this temperature region as region III, where the ripple periodicity increases dramatically toward the main transition temperature. In region II, between regions I and III, the ripple periodicity decreases gradually with temperature. This behavior is quite similar to that of pure DMPC. Temperature-versus-ripple periodicity curves are parallel among pure DMPC and DMPCs with various cholesterol contents. We explain this behavior in terms of a model proposed by other workers.     

Fourier transform infrared-attenuated total reflection spectroscopy of hydration of dimyristoylphosphatidylcholine multibilayers

The effect of hydration on the structure and molecular orientation of multibilayers of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), cast on a germanium plate, was studied by means of polarized Fourier transform infrared (FT-IR)-attenuated total reflection spectroscopy. Compared with the dry state, the antisymmetric and symmetric CH2 stretching bands of fully hydrated DMPC in the liquid-crystalline state were shifted to the higher frequency side, indicating the increase in the number of the gauche conformers. However, the dichroism of these bands revealed that the hydrocarbon chains of DMPC were still ordered and titled. The absorption bands of the glycerol ester, phosphoryl, and choline groups were broadened upon hydration, suggesting the activation of the librational or torsional motion. Furthermore, the dichroism of the polar head group bands of DMPC indicated that these groups retained a slight orientation even in the fully hydrated and fluid multibilayers.     

Temperature dependence of the ripple structure in dimyristoylphosphatidylcholine studied by synchrotron X-ray small-angle diffraction

The ripple structure of 1,2-dimyristoyl-L-phosphatidylcholine (DMPC) multibilayer containing excess water (60 wt%) was studied by synchrotron X-ray small-angle diffraction. The (0,1) spacing which corresponds to the ripple repeat distance depends on temperature: At 13 degrees C the (0,1) spacing is 14.15 nm, the spacing decreases at higher temperatures and reaches 12.1 nm at 23.5 degrees C, just below the main transition temperature. The spacing is in good agreement between heating process and cooling process except for the supercooling region. The result suggests that the rearrangement of the ripple structure takes place during temperature change successively. The Landau-de Gennes free energy equation explains well the temperature dependence of the ripple repeat distance.     

Thermal effects on motion and orientation of the cholestane spin label in planar multibilayers of dimyristoylphosphatidylcholine and dipalmitoylphosphatidylcholine

A detailed picture of the orientation and restricted motion of the cholestane spin label (3-spiro-doxyl-5α-cholestane) in planar multibilayers of dipalmitoylphosphatidylcholine and dimyristoylphosphatidylcholine has been recorded by simultaneous simulation of ESR spectra obtained with the magnetic field parallel and perpendicular to the bilayers (Shimoyama, Y., Eriksson, L.E.G. and Ehrenberg, A. (1978) Biochim. Biophys. Acta 508, 213–235). The analysis has been made over the temperature range ?30°C to 60°C on samples containing 20 to 22% water. At low temperatures the cholestane spin label is tilted with respect to the lipid bilayer normal by an angle of approx. 30° which disappears at the pretransition. In this low temperature range the restricted twisting motion has an activation energy of 5.5 kJ·mol^?1. Above the main transition the twisting motion is unrestricted and has the activation energy 20 kJ·mol^?1. From below the pretransition to above the main transition the velocity of the twisting motion increases by an order of magnitude. The amplitude of the wobbling motion increases abruptly from 0° to 35° at the main transition.     

Adsorbed to a rigid substrate, dimyristoylphosphatidylcholine multibilayers attain full hydration in all mesophases.

Whether hydrated from vapor or immersed in liquid water, aligned multibilayers of dimyristoylphosphatidylcholine adsorbed to a single mica "substrate" are shown by neutron diffraction to hydrate in all mesophases (e.g., Lbeta', Pbeta', and Lalpha) to the same extent as their liposomal counterparts suspended in liquid water. These data clearly demonstrate that the commonly accepted vapor pressure paradox does not exist.     

Temperature dependence of blood surface tension

Whole blood surface tension of 15 healthy subjects recorded by the ring method was investigated in the temperature range from 20 to 40 degrees C. The surface tension omega as a function of temperature t ( degrees C) is described by an equation of linear regression as omega(t) = (-0.473 t + 70.105) x 10(-3) N/m. Blood serum surface tension in the range from 20 to 40 degrees C is described by linear regression equation omega(t) = (-0.368 t + 66.072) x 10(-3) N/m and linear regression function of blood sediment surface tension is omega(t) = (-0.423 t + 67.223) x10(-3) N/m.     

Temperature dependence of ADP/ATP translocation in mitochondria

The temperature dependence of the adenine nucleotide exchange in mitochondria has been determined by employing a rapid mixing, quenching and sampling apparatus and the inhibitor quench-back exchange method. Thus the exchange is resolved down to 0.1 s. Rates are evaluated from accumulating the time-dependent progress at about 10 points. The exchange rate in liver mitochondria was determined from -10 degrees C to + 10 degrees C in the presence of 20% glycol, from 0 degrees C to 25 degrees C, and from 20 degrees C to 40 degrees C under partial inhibition by carboxyatractylate. The total range between -10 degrees C to + 40 degrees C has only one temperature break at 13 degrees C. From the Arrhenius plot between -10 degrees C to + 13 degrees C, EA approximately equal to 140 kJ and above 13 degrees C, EA approximately equal to 56 kJ is evaluated, corresponding to a Q10 of 8 and 2 respectively. In beef heart mitochondria the exchange rate was measured between 0 degrees C and 20 degrees C, and between 15 degrees C and 30 degrees C under partial inhibition with carboxyatractylate. There is a temperature break around 14 degrees C with EA approximately equal to 143 kJ between 0 degrees C and 14 degrees C and EA approximately equal to 60 kJ from 15 degrees C to 30 degrees C. The extrapolated translocation rates at 37 degrees C are 500 and 1800 mumol min-1 (g protein)-1 for rat liver and for beef heart mitochondria respectively. The temperature break is suggested to reflect a conformation change since there is no reversed break at low temperature, the temperature break changes in sonic particles and no lipid phase transition at 14 degrees C in mitochondria has been reported.     

Local anesthetic-phospholipid interactions. The pH dependence of the binding of dibucaine to dimyristoylphosphatidylcholine vesicles

The interaction of the local anesthetic dibucaine with unilamellar vesicles of dimyristoylphosphatidylcholine was studied by equilibrium dialysis. Saturating binding profiles (as a function of dibucaine) were found, with apparent association constant ranging from 1.26 X 10(3)M-1 to 2.57 X 10(3)M-1 as pH is increased from 5.0 to 7.5. The number of phospholipid molecules comprising a binding site was found to be about 5 at each pH. Analysis of the data was also achieved using the Stern model, which takes into account the electrostatic effect on binding of the cationic drug due to the build up of a surface potential.     

Time-dependent changes in the size distribution of distearoylphosphatidylcholine vesicles.

The results of transmission electron microscopic and ultracentrifugal studies of the size distributions of sonicated distearoylphosphatidylcholine vesicles are reported. Small vesicles (d approximately 300 A) were prepared by sonication of pure 1,2-distearoyl-3-sn-phosphatidylcholine in water and incubated at 4, 21, 40, 53, and 65 degrees C. The vesicle size distributions changed as a function of time at all temperatures below the phase-transition temperature but remained constant at the transition temperature and above. The sizes of structures to which the small vesicles are converted are the same at all temperatures, although the rates of conversion differ. The primary structures formed are identified as larger vesicles. The rate of loss of small vesicles is found to increase with decreasing temperature. At 4 and 21 degrees C small vesicles are converted to amorphous material, possibly irregular fragments of neat phase, in addition to being converted to larger vesicles. Trace amounts of an impurity commonly produced in the synthesis of 1,2-distearoyl-3-sn-phosphatidylcholine, 1,3-distearoyl-2-sn-phosphatidylcholine, are found to dramatically reduce the rate of loss of small vesicles at 21 degrees C.     

Molecular sorting of lipids by bacteriorhodopsin in dilauroylphosphatidylcholine/distearoylphosphatidylcholine lipid bilayers.

A combined experimental and theoretical study is performed on binary dilauroylphosphatidylcholine/distearoylphosphatidylcholine (DLPC/DSPC) lipid bilayer membranes incorporating bacteriorhodopsin (BR). The system is designed to investigate the possibility that BR, via a hydrophobic matching principle related to the difference in lipid bilayer hydrophobic thickness and protein hydrophobic length, can perform molecular sorting of the lipids at the lipid-protein interface, leading to lipid specificity/selectivity that is controlled solely by physical factors. The study takes advantage of the strongly nonideal mixing behavior of the DLPC/DSPC mixture and the fact that the average lipid acyl-chain length is strongly dependent on temperature, particularly in the main phase transition region. The experiments are based on fluorescence energy transfer techniques using specifically designed lipid analogs that can probe the lipid-protein interface. The theoretical calculations exploit a microscopic molecular interaction model that embodies the hydrophobic matching as a key parameter. At low temperatures, in the gel-gel coexistence region, experimental and theoretical data consistently indicate that BR is associated with the short-chain lipid DLPC. At moderate temperatures, in the fluid-gel coexistence region, BR remains in the fluid phase, which is mainly composed of short-chain lipid DLPC, but is enriched at the interface between the fluid and gel domains. At high temperatures, in the fluid phase, BR stays in the mixed lipid phase, and the theoretical data suggest a preference of the protein for the long-chain DSPC molecules at the expense of the short-chain DLPC molecules. The combined results of the experiments and the calculations provide evidence that a molecular sorting principle is active because of hydrophobic matching and that BR exhibits physical lipid selectivity. The results are discussed in the general context of membrane organization and compartmentalization and in terms of nanometer-scale lipid-domain formation.     

Temperature dependence of the functional response

The Arrhenius equation has emerged as the favoured model for describing the temperature dependence of consumption in predator-prey models. To examine the relevance of this equation, we undertook a meta-analysis of published relationships between functional response parameters and temperature. We show that, when plotted in lin-log space, temperature dependence of both attack rate and maximal ingestion rate exhibits a hump-shaped relationship and not a linear one as predicted by the Arrhenius equation. The relationship remains significantly downward concave even when data from temperatures above the peak of the hump are discarded. Temperature dependence is stronger for attack rate than for maximal ingestion rate, but the thermal optima are not different. We conclude that the use of the Arrhenius equation to describe consumption in predator-prey models requires the assumption that temperatures above thermal optima are unimportant for population and community dynamics, an assumption that is untenable given the available data.     

Temperature dependence of photosynthesis in cotton

Cotton plants (Gossypium hirsutum L., var. Deltapine Smooth Leaf) were grown under controlled environmental conditions over a range of day/night temperatures from 20/15 to 40/35 C. Their photosynthetic characteristics were then measured over a comparable temperature range. Net photosynthesis tended stongly to be greatest, and intracellular resistance to CO₂ transport to be lowest, when the measurement temperature corresponded to the daytime growth temperature, suggesting pronounced acclimation of the plants to the growth temperature. The preferred growth temperature was close to the 25/20 C regime, since net photosynthesis of these plants, regardless of measurement temperature, was higher and intracellular resistance lower, than in plants from any other regime.     

Fasciola gigantica: surface topography of the adult tegument

Adult Fasciola gigantica are leaf-shaped with tapered anterior and posterior ends and measure about 35 mm in length and 15 mm in width across the mid section. Under the scanning electron microscope its surface appears rough due to the presence of numerous spines and surface foldings. Both oral and ventral suckers have thick rims covered with transverse folds and appear spineless. On the anterior part of the ventral surface of the body, the spines are small and closely-spaced. Each spine has a serrated edge with 16 to 20 sharp points, and measures about 20 microm in width and 30 microm in height. In the mid-region the spines increase in size (up to 54 microm in width and 58 microm in height) and number, especially towards the lateral aspect of the body. Towards the posterior end the spines progressively decrease in both size and number. The tegumental surface between the spines appears highly corrugated with transverse folds alternating with grooves. At higher magnifications the surface of each fold is further increased with a meshwork of small ridges separated by variable-sized pits or slits. There are three types of sensory papillae on the surface. Types 1 and 2 are bulbous, measuring 4-6 microm in diameter at the base with nipple-like tips, and the type 2 also have short cilia. Type 3 papillae are also bulbous and of similar size but with a smooth surface. These sensory papillae usually occur in clusters, each having between 2 and 15 units depending on the region of the body. Clusters of papillae on the lateral aspect (usually types 1 and 2) and around the suckers (type 3) tend to be more numerous and larger in size. The dorsal side of the body exhibits similar surface features, but the spines and papillae appear less numerous and are smaller. Corrugation and invaginations of the surface are also less extensive than on the ventral side of the body.     

Transmembrane localization of cis-isomers of zeaxanthin in the host dimyristoylphosphatidylcholine bilayer membrane

The effects of the 9-cis and 13-cis isomers of zeaxanthin on the molecular organization and dynamics of dimyristoylphosphatidylcholine (DMPC) membranes were investigated using conventional and saturation recovery EPR observations of the 1-palmitoyl-2-(14-doxylstearoyl)phosphatidylcholine (14-PC) spin label. The results were compared with the effects caused by the all-trans isomer of zeaxanthin. Effects on membrane fluidity, order, hydrophobicity, and the oxygen transport parameter were monitored at the center of the fluid phase DMPC membrane. The local diffusion-solubility product of oxygen molecules (oxygen transport parameter) in the membrane center, studied by saturation-recovery EPR, decreased by 47% and 27% by including 10 mol% 13-cis and 9-cis zeaxanthin, respectively; whereas, incorporation of all-trans zeaxanthin decreased this parameter by only 11%. At a zeaxanthin-to-DMPC mole ratio of 1:9, all investigated isomers decreased the membrane fluidity and increased the alkyl chain order in the membrane center. They also increased the hydrophobicity of the membrane interior. The effects of these isomers of zeaxanthin on the membrane properties mentioned above increase as: all-trans < 9-cis ≤ 13-cis. Obtained results suggest that the investigated cis-isomers of zeaxanthin, similar to the all-trans isomer, are located in the membrane interior, adopting transmembrane orientation with the polar terminal hydroxyl groups located in the opposite leaflets of the bilayer. However, the existence of the second pool of cis-zeaxanthin molecules located in the one leaflet and anchored by the terminal hydroxyl groups in the same polar headgroup region cannot be completely ruled out.     

The surface topography of a monogenean Heterapta chorinemi from the gills of Scomberoides commersonianus

and 1986. The surface topography of a monogenean Heterapta chorinemi from the gills of Scomberoides commersonianus. International Journal for Parasitology 16: 595–600. The dorsal and ventral surfaces of H. chorinemi bear microvilli and boss-like structures. These may increase the surface area for respiratory gaseous exchange and absorption of nutrients from the surrounding medium. Uniciliated sensory endings, presumably rheoreceptors, are present over the entire surface whereas non-ciliated structures, possibly mechanoreceptors, are present only on the ventral surface of the haptor. The haptor possesses 6–10 pairs of pincer-type clamps and 30–40 pairs of open sucker-type clamps with scleritized jaws. The common genital atrium is situated on the ventral surface, the vaginal pore opens on the dorsal surface and the mouth is subterminal as described in previous light microscope studies.     

Temperature dependence of the enzyme-substrate recognition mechanism

We determined the crystal structure of the liganded form of alpha-aminotransferase from a hyperthermophile, Pyrococcus horikoshii. This hyperthermophilic enzyme did not show domain movement upon binding of an acidic substrate, glutamate, except for a small movement of the alpha-helix from Glu16 to Ala25. The omega-carboxyl group of the acidic substrate was recognized by Tyr70* without its side-chain movement, but not by positively charged Arg or Lys. Compared with the homologous enzymes from Thermus thermophilus HB8 and Escherichia coli, it was suggested that the more thermophilic the enzyme is, the smaller the domain movement is. This rule seems to be applicable to many other enzymes already reported.     

Temperature dependence of the photoresponse ofHalobacterium halobium

The temperature dependence of the phototactic behavior of bacteriorhodopsin-pigmentedHalobacterium halobium was measured separately toward attractive yellow-green and repellent violet light. A switchoff phenomenon was found for the former below ca. 27°C, while the response to the latter was constant down to about 7°C. This agreement between the transition temperature for the attractive photosystem with that observed in vitro for several properties of purple membrane, of which bacteriorhodopsin is the sole protein pigment, supports the idea that the attractive photosystem is associated with bacteriorhodopsin. Conversely, the absence of such a transition for the photosystem controlling photorepulsion confirms the separate identity of the two photosystems.