Propagation Speed in Myelinated Nerve: I. Experimental Dependence on External Na+ and on Temperature

Conduction speed (θ) in single myelinated Rana pipiens sciatic nerve fibers has been precisely measured using intracellular recording and on-line digital computer techniques. The dependence of relative speed on external Na concentration at 15°C has been found to be ln(θ₁/θ₂) = 0.524 (±0.018) ln ([Na⁺]₁/[Na⁺]₂) + 0.003. Thus θ has very close to a square root dependence on [Na⁺]₀ for these fibers. This experimental finding is not in complete agreement with a theoretical prediction based on a solution of the Hodgkin-Huxley (H.H.) equations. The effect of small temperature variations around 15°C on θ has also been measured for Rana fibers in Ringer's solution. θ has close to an exponential dependence on T and a Q₁₀ of 2.95 has been estimated.     

Effects of temperature on the phase behavior and permeability of thylakoid lipid vesicles : relevance to chilling stress

Large unilamellar vesicles composed of thylakoid glycolipids, phosphatidylglycerol, and varying proportions of dipalmitoylphosphatidylglycerol (DPPG) have been examined for the temperature dependence of their permeability to ⁸⁶Rb⁺ and for the occurrence of liquid-crystalline to gel (L_α-to-L_β) phase separations. In vesicles in which the normal 12 mole percent of moderately unsaturated thylakoid phosphatidylglycerol was partially or completely replaced by DPPG, analysis by differential scanning calorimetry indicated that an L_α-to-L_β phase separation did not occur between 0 and 60°C. However, in similar vesicle dispersions that were first subjected to a freeze-thaw cycle, L_α-to-L_β phase separations were observed to occur between 17 and 53°C. The temperature and enthalpy of these phase separations were closely related to the proportion of DPPG in the original lipid mixture. In parallel experiments, large unilamellar vesicles were measured for their permeability to ⁸⁶Rb⁺ between 7 and 30°C. There were no systematic increases in permeability to ⁸⁶Rb⁺ as a function of DPPG content at the temperatures relevant to chilling stress in higher plants. It is concluded that (a) L_α-to-L_β phase separations do not occur in well-defined galactolipid vesicles containing ≤12 mole percent DPPG between 0 and 60°C and (b) these vesicles show no alterations in permeability to ⁸⁶Rb⁺ between 7 and 30°C that are relevant to chilling stress in higher plants.     

Influence of a Decaying Cyclonic Eddy on Biogenic Silica and Particulate Organic Carbon in the Tropical South China Sea Based on 234Th-238U Disequilibrium

Eddies play a critical role in regulating the biological pump by pumping new nutrients to the euphotic zone. However, the effects of cyclonic eddies on particle export are not well understood. Here, biogenic silica (BSi) and particulate organic carbon (POC) exports were examined inside and outside a decaying cyclonic eddy using ²³⁴Th-²³⁸U disequilibria in the tropical South China Sea. For the eddy and outside stations, the average concentrations of BSi in the euphotic zone were 0.17±0.09 μmol L^-1 (mean±sd, n = 20) and 0.21±0.06 μmol L^-1 (n = 34). The POC concentrations were 1.42±0.56 μmol L^-1 (n = 34) and 1.30±0.46 μmol L^-1 (n = 51). Both BSi and POC abundances did not show change at the 95% confidence level. Based on the ²³⁴Th-²³⁸U model, BSi export fluxes in the eddy averaged 0.18±0.15 mmol Si m^-2 d^-1, which was comparable with the 0.40±0.20 mmol Si m^-2 d^-1 outside the eddy. Similarly, the average POC export fluxes were 1.5±1.4 mmol C m^-2 d^-1 and 1.9±1.3 mmol C m^-2 d^-1 for the eddy and outside stations. From these results we concluded that cyclonic eddies in their decaying phase have little effect on the abundance and export of biogenic particles.     

Immobilised Histidine Tagged β 2-Adrenoceptor Oriented by a Diazonium Salt Reaction and Its Application in Exploring Drug-Protein Interaction Using Ephedrine and Pseudoephedrine as Probes

A new oriented method using a diazonium salt reaction was developed for linking β ₂-adrenoceptor (β ₂-AR) on the surface of macroporous silica gel. Stationary phase containing the immobilised receptor was used to investigate the interaction between β ₂-AR and ephedrine plus pseudoephedrine by zonal elution. The isotherms of the two drugs best fit the Langmuir model. Only one type of binding site was found for ephedrine and pseudoephedrine targeting β ₂-AR. At 37 °C, the association constants during the binding were (5.94±0.05)×10³/M for ephedrine and (3.80±0.02) ×10³/M for pseudoephedrine, with the binding sites of (8.92±0.06) ×10⁻⁴ M. Thermodynamic studies showed that the binding of the two compounds to β ₂-AR was a spontaneous reaction with exothermal processes. The ΔG^θ, ΔH^θ and ΔS^θ for the interaction between ephedrine and β ₂-AR were −(22.33±0.04) kJ/mol, −(6.51±0.69) kJ/mol and 50.94±0.31 J/mol·K, respectively. For the binding of pseudoephedrine to the receptor, these values were −(21.17±0.02) kJ/mol, −(7.48±0.56) kJ/mol and 44.13±0.01 J/mol·K. Electrostatic interaction proved to be the driving force during the binding of the two drugs to β ₂-AR. The proposed immobilised method will have great potential for attaching protein to solid substrates and realizing the interactions between proteins and drugs.     

Primary Events, Energy Transfer, and Reactions in Photosynthetic Units: Lifetime of the Excited State In Vivo: I. Chlorophyll a in Algae, at Room and at Liquid Nitrogen Temperatures; Rate Constants of Radiationless Deactivation and Trapping

Using a mode-locked laser (λ, 632.8 nm), fluorescence decay of chlorophyll (Chl) a in the green alga Chlorella pyrenoidosa, the red alga Porphyridium cruentum, and the blue-green alga Anacystis nidulans was measured by the phase-shift method under conditions when photosynthesis was not operative (3-(3,4-dichlorophenyl)-1,1-dimethylurea [DCMU] poisoning, or cooling to 77°K). In the presence of 10^-5 M DCMU, the lifetime of Chl a fluorescence (τ) at room temperature is about 1.7 nsec in Chlorella, 1.0 nsec in Porphyridium, and 0.7 nsec in Anacystis. At 77°K, τ is 1.4 nsec (for fluorescence at about 685 nm, F-685) and 2.3 nsec (for F-730) in Chlorella, 0.9 nsec (F-685) and 1.2 nsec (F-730) in Porphyridium, and 0.8 nsec (F-685 and F-730) in Anacystis. From the above measurement, and the assumption that τ₀ (the intrinsic fluorescence lifetime) for Chl a in all three algae is 15.2 nsec, we have calculated the rate constants of radiationless transition (that includes energy transfer to weakly fluorescent system I) processes competing with fluorescence at room temperature to be about 5 × 10⁸ sec^-1 in Chlorella, 9 × 10⁸ sec^-1 in Porphyridium, and 13 × 10⁸ sec^-1 in Anacystis. At 77°K, this rate constant for Chl a that fluoresces at 685 nm remains, in the first approximation, the same as at room temperature. From the τ data, the rate constant for the trapping of excitation energy is calculated to be about 1.2 × 10⁹ sec^-1 for Chlorella, 2 × 10⁹ sec^-1 for Porphyridium, and 2 × 10⁹ sec^-1 for Anacystis. The efficiency of trapping is calculated to be about 66% (Chlorella), 68% (Porphyridium), and 60% (Anacystis). (It is recognized that variations in the above values are to be expected if algae grown under different conditions are used for experimentation.) The maximum quantum yield of Chl a fluorescence for system II (λ, 632.8 nm), calculated from τ measurements, is about 10% in Chlorella, 6-7% in Porhyridium, and 5% in Anacystis under conditions when photosynthesis is not operative; the values at 77°K appear to be very close to those with DCMU added at room temperature. ø for F-730 at 77°K, however, is somewhat higher than for F-685. The predicted quantum yields of fluorescence for Chl a in intact cells (both systems I and II) at low intensities of 632.8 nm light are about 2-3, 1-2, and 1% for Chlorella, Porphyridium, and Anacystis, respectively.     

A study of lipid bilayer membrane stability using precise measurements of specific capacitance

A method is described for measuring the specific capacitance (C_m) of lipid bilayer membranes with an estimated experimental error of only 1%. The gross capacitance was measured with an AC Wheatstone bridge and a photographic technique was used to determine the area of thin membrane. The results of measurements on oxidized cholesterol-decane membranes formed in 1 × 10^-2 M KCl show that C_m depends upon temperature, voltage, time, and the age of the bulk membrane solutions. For a freshly thinned membrane (from 5 week old solution), C_m increases exponentially from an initial value of 0.432 ±0.021 (SD) μF/cm² with a time constant of ~15 min. A 100 mv potential applied across the membrane for 10-20 min prior to making measurements eliminated this time dependence and produced final-state membranes. C_m of final-state membranes depends upon applied voltage (V_a) and obeys the equation C_m = C₀ + βV_a² where V_a V_DC + V^rms_AC. C₀ and β depend upon temperature; C₀ decreases linearly with temperature while β increases linearly. At 20°C, C₀ = 0.559 ±0.01 (SD) μF/cm² and β = 0.0123 ±0.0036 (SD) (μF/cm²)/(mv²) and at 34°C, C₀ = 0.472 ±0.01 and β = 0.0382 ±0.0039. These variations in C_m are interpreted as resulting from thickness changes. The possibility that they result from diffuse layer and/or membrane dielectric phenomena is discussed and found to be unlikely. The results are discussed in terms of membrane stability by constructing hypothetical potential energy vs. thickness curves.     

Long-Range Correlations of Global Sea Surface Temperature

Scaling behaviors of the global monthly sea surface temperature (SST) derived from 1870–2009 average monthly data sets of Hadley Centre Sea Ice and SST (HadISST) are investigated employing detrended fluctuation analysis (DFA). The global SST fluctuations are found to be strong positively long-range correlated at all pertinent time-intervals. The value of scaling exponent is larger in the tropics than those in the intermediate latitudes of the northern and southern hemispheres. DFA leads to the scaling exponent α = 0.87 over the globe (60°S~60°N), northern hemisphere (0°N~60°N), and southern hemisphere (0°S~60°S), α = 0.84 over the intermediate latitude of southern hemisphere (30°S~60°S), α = 0.81 over the intermediate latitude of northern hemisphere (30°N~60°N) and α = 0.90 over the tropics 30°S~30°N [fluctuation F(s) ~ s^α], which the fluctuations of monthly SST anomaly display long-term correlated behaviors. Furthermore, the larger the standard deviation is, the smaller long-range correlations (LRCs) of SST in the corresponding regions, especially in three distinct upwelling areas. After the standard deviation is taken into account, an index χ = α * σ is introduced to obtain the spatial distributions of χ. There exists an obvious change of global SST in central east and northern Pacific and the northwest Atlantic. This may be as a clue on predictability of climate and ocean variabilities.     

In Intact Cone Photoreceptors,a Ca2+-dependent,Diffusible Factor Modulates the cGMP-gated Ion Channels Differently than in Rods

We investigated the modulation of cGMP-gated ion channels in single cone photoreceptors isolated from a fish retina. A new method allowed us to record currents from an intact outer segment while controlling its cytoplasmic composition by superfusion of the electropermeabilized inner segment. The sensitivity of the channels to agonists in the intact outer segment differs from that measured in membrane patches detached from the same cell. This sensitivity, measured as the ligand concentration necessary to activate half-maximal currents, K _1/2, also increases as Ca²⁺ concentration decreases. In electropermeabilized cones, K _1/2 for cGMP is 335.5 ± 64.4 μM in the presence of 20 μM Ca²⁺, and 84.3 ± 12.6 μM in its absence. For 8Br-cGMP, K _1/2 is 72.7 ± 11.3 μM in the presence of 20 μM Ca²⁺ and 15.3 ± 4.5 μM in its absence. The Ca²⁺-dependent change in agonist sensitivity is larger in extent than that measured in rods. In electropermeabilized tiger salamander rods, K _1/2 for 8Br-cGMP is 17.9 ± 3.8 μM in the presence of 20 μM Ca²⁺ and 7.2 ± 1.2 μM in its absence. The Ca²⁺-dependent modulation is reversible in intact cone outer segments, but is progressively lost in the absence of divalent cations, suggesting that it is mediated by a diffusible factor. Comparison of data in intact cells and detached membrane fragments from cones indicates that this factor is not calmodulin. At 40 μM 8Br-cGMP, the Ca²⁺-dependent change in sensitivity in cones is half-maximal at K _Ca = 286 ± 66 nM Ca²⁺. In rods, by contrast, K _Ca is ∼50 nM Ca²⁺. The difference in magnitude and Ca²⁺ dependence of channel modulation between photoreceptor types suggests that this modulation may play a more significant role in the regulation of photocurrent gain in cones than in rods.     

Ethylene Removal at Low Temperatures under Biofilter and Batch Conditions

Removal of the plant hormone ethylene (C₂H₄) is often required by horticultural storage facilities, which are operated at temperatures below 10°C. The aim of this study was to demonstrate an efficient, biological C₂H₄ removal under such low-temperature conditions. Peat-soil, acclimated to degradation of C₂H₄, was packed in a biofilter (687 cm³) and subjected to an airflow (~73 ml min⁻¹) with 2 ppm (μl liter⁻¹) C₂H₄. The C₂H₄ removal efficiencies achieved at 20, 10, and 5°C, respectively, were 99.0, 98.8, and 98.4%. This corresponded to C₂H₄ levels of 0.022 to 0.032 ppm in the biofilter outlet air. At 2°C, the average C₂H₄ removal efficiency dropped to 83%. The detailed temperature response of C₂H₄ removal was tested under batch conditions by incubation of 1-g soil samples in a temperature gradient ranging from 0 to 29°C with increments of 1°C. The C₂H₄ removal rate was highest at 26°C (0.85 μg of C₂H₄ g [dry weight]⁻¹ h⁻¹), but remained at levels of 0.14 to 0.28 μg of C₂H₄ g (dry weight)⁻¹ h⁻¹ at 0 to 10°C. At 35 to 40°C, the C₂H₄ removal rate was negligible (0.02 to 0.06 μg of C₂H₄ g [dry weight]⁻¹ h⁻¹). The Q₁₀ (i.e., the ratio of rates 10°C apart) for C₂H₄ removal was 1.9 for the interval 0 to 10°C. In conclusion, the present results demonstrated microbial C₂H₄ removal, which proceeded at 0 to 2°C and produced a moderately psychrophilic temperature response.     

Quasielastic Light-Scattering Study on Changes in Sizes of Native White Membranes after Addition of Retinal

Aqueous suspensions of native white membranes from Halobacterium halobium, strain JW2N, have been studied by quasielastic light scattering. The intensity autocorrelation functions of polarized scattered light from suspensions of white membranes themselves and of white membranes after reconstitution with retinal were measured at various K², K being the magnitude of the scattering vector. The first cumulant or the average decay rate of the correlation function was obtained by a cumulant expansion method. The first cumulant for the white membranes increased after retinal was added to the suspension. The first cumulants obtained before and after the addition of retinal were almost independent of pH in the range 7 to 11, and of temperature in the range 15° to 40°C after T/η scaling, η being the solvent viscosity. This suggests that photocycling in reconstituted membranes, induced by the probe laser-beam, did not cause any detectable change in spectra, and that the membrane flexibility, if present, was independent of the above conditions, so that the spectral changes after the addition of retinal could be attributed mostly to the changes in the sizes of the membranes. A theoretical formulation for the first cumulant for a rigid disk-like scatterer (Fujime, S. and K. Kubota, 1985, Biophys. Chem., 23:1-13.) was applied to the analysis of the spectra. The results suggest that the radii of the membrane patches decreased by several percent after the addition of retinal.     

Spatial patterns of leaf δ13C and δ15N of aquatic macrophytes in the arid zone of northwestern China

Analysis of stable isotope composition is an important tool in research on plant physiological ecology. However, large‐scale patterns of leaf‐stable isotopes for aquatic macrophytes have received considerably less attention. In this study, we examined the spatial pattern of stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N) of macrophytes leaves collected across the arid zone of northwestern China (approximately 2.4 × 10⁶ km²) and attempted to illustrate its relationship with environmental factors (i.e., temperature, precipitation, potential evapotranspiration, sediment total carbon and nitrogen). Our results showed that the mean values of the leaf δ¹³C and δ¹⁵N in the macrophytes sampled from the arid zone were −24.49‰ and 6.82‰, respectively, which were far less depleted than those measured of terrestrial plants. The order of averaged leaf δ¹³C from different life forms was as follows: submerged > floating‐leaved > emergent. Additionally, our studies indicated that the values of foliar δ¹³C values of all the aquatic macrophytes were only negatively associated with precipitation, but the foliar δ¹⁵N values were mainly associated with temperature, precipitation, and potential evapotranspiration. Therefore, we speculated that water‐relation factors are the leaf δ¹³C determinant of macrophytes in the arid zone of northwestern China, and the main factors affecting leaf δ¹⁵N values are the complex combination of water and energy factors.     

Sro9, a Multicopy Suppressor of the Bud Growth Defect in the Saccharomyces Cerevisiae Rho3-Deficient Cells, Shows Strong Genetic Interactions with Tropomyosin Genes, Suggesting Its Role in Organization of the Actin Cytoskeleton

RHO3 encodes a Rho-type small GTPase in the yeast Saccharomyces cerevisiae and is involved in the proper organization of the actin cytoskeleton required for bud growth. SRO9 (YCL37c) was isolated as a multicopy suppressor of a rho3δ mutation. An Sro9p domain required for function is similar to a domain in the La protein (an RNA-binding protein). Disruption of SRO9 did not affect vegetative growth, even with the simultaneous disruption of an SRO9 homologue, SRO99. However, sro9δ was synthetically lethal with a disruption of TPM1, which encodes tropomyosin; sro9δ tpm1δ cells did not distribute cortical actin patches properly and lysed. We isolated TPM2, the other gene for tropomyosin, as a multicopy suppressor of a tpm1δ sro9δ double mutant. Genetic analysis suggests that TPM2 is functionally related to TPM1 and that tropomyosin is important but not essential for cell growth. Overexpression of SRO9 suppressed the growth defect in tpm1δ tpm2δ cells, disappearance of cables of actin filaments in both rho3δ cells and tpm1δ cells, and temperature sensitivity of actin mutant cells (act1-1 cells), suggesting that Sro9p has a function that overlaps or is related to tropomyosin function. Unlike tropomyosin, Sro9p does not colocalize with actin cables but is diffusely cytoplasmic. These results suggest that Sro9p is a new cytoplasmic factor involved in the organization of actin filaments.     

Cooling Reduces cAMP-Stimulated Exocytosis and Adiponectin Secretion at a Ca2+-Dependent Step in 3T3-L1 Adipocytes

We investigated the effects of temperature on white adipocyte exocytosis (measured as increase in membrane capacitance) and short-term adiponectin secretion with the aim to elucidate mechanisms important in regulation of white adipocyte stimulus-secretion coupling. Exocytosis stimulated by cAMP (included in the pipette solution together with 3 mM ATP) in the absence of Ca²⁺ (10 mM intracellular EGTA) was equal at all investigated temperatures (23°C, 27°C, 32°C and 37°C). However, the augmentation of exocytosis induced by an elevation of the free cytosolic [Ca²⁺] to ~1.5 μM (9 mM Ca²⁺ + 10 mM EGTA) was potent at 32°C or 37°C but less distinct at 27°C and abolished at 23°C. Adiponectin secretion stimulated by 30 min incubations with the membrane permeable cAMP analogue 8-Br-cAMP (1 mM) or a combination of 10 μM forskolin and 200 μM IBMX was unaffected by a reduction of temperature from 32°C to 23°C. At 32°C, cAMP-stimulated secretion was 2-fold amplified by inclusion of the Ca²⁺ ionophore ionomycin (1μM), an effect that was not observed at 23°C. We suggest that cooling affects adipocyte exocytosis/adiponectin secretion at a Ca²⁺-dependent step, likely involving ATP-dependent processes, important for augmentation of cAMP-stimulated adiponectin release.     

Photosynthetic Response of Soybean to Microclimate in 26-Year-Old Tree-Based Intercropping Systems in Southern Ontario,Canada

In order to study the effect of light competition and microclimatic modifications on the net assimilation (NA), growth and yield of soybean (Glycine max L.) as an understory crop, three 26-year-old soybean-tree (Acer saccharinum Marsh., Populus deltoides X nigra, Juglans nigra L.) intercropping systems were examined. Tree competition reduced photosynthetically active radiation (PAR) incident on soybeans and reduced net assimilation, growth and yield of soybean. Soil moisture of 20 cm depth close (< 3 m) to the tree rows was also reduced. Correlation analysis showed that NA and soil water content were highly correlated with growth and yield of soybean. When compared with the monoculture soybean system, the relative humidity (RH) of the poplar-soybean, silver maple-soybean, and black walnut-soybean intercropped systems was increased by 7.1%, 8.0% and 5.9%, soil water content was reduced by 37.8%, 26.3% and 30.9%, ambient temperature was reduced by 1.3°C, 1.4°C and 1.0°C, PAR was reduced by 53.6%, 57.9% and 39.9%, and air CO₂ concentration was reduced by 3.7μmol·mol^-1, 4.2μmol·mol^-1 and 2.8μmol·mol^-1, respectively. Compared to the monoculture, the average NA of soybean in poplar, maple and walnut treatments was also reduced by 53.1%, 67.5% and 46.5%, respectively. Multivariate stepwise regression analysis showed that PAR, ambient temperature and CO₂ concentration were the dominant factors influencing net photosynthetic rate.     

Visual Pigments of Goldfish Cones : Spectral Properties and Dichroism

Freshly isolated retinal photoreceptors of goldfish were studied microspectrophotometrically. Absolute absorptance spectra obtained from dark-adapted cone outer segments reaffirm the existence of three spectrally distinct cone types with absorption maxima at 455 ± 3,530 ± 3, and 625 ± 5 nm. These types were found often recognizable by gross cellular morphology. Side-illuminated cone outer segments were dichroic. The measured dichroic ratio for the main absorption band of each type was 2–3:1. Rapidly bleached cells revealed spectral and dichroic transitions in regions near 400–410, 435–455, and 350–360 nm. These photoproducts decay about fivefold as fast as the intermediates in frog rods. The spectral maxima of photoproducts, combined with other evidence, indicate that retinene₂ is the chromophore of all three cone pigments. The average specific optical density for goldfish cone outer segments was found to be 0.0124 ± 0.0015/µm. The spectra of the blue-, and green-absorbing cones appeared to match porphyropsin standards with half-band width Δν = 4,832 ± 100 cm^–1. The red-absorbing spectrum was found narrower, having Δν = 3,625 ± 100 cm^–1. The results are consistent with the notion that visual pigment concentration within the outer segments is about the same for frog rods and goldfish cones, but that the blue-, and green-absorbing pigments possess molar extinctions of 30,000 liter/mol cm. The red-absorbing pigment was found to have extinction of 40,000 liter/mol cm, assuming invariance of oscillator strength among the three cone spectra.     

Detection of Phosphatidylcholine-Coated Gold Nanoparticles in Orthotopic Pancreatic Adenocarcinoma using Hyperspectral Imaging

Nanoparticle uptake and distribution to solid tumors are limited by reticuloendothelial system systemic filtering and transport limitations induced by irregular intra-tumoral vascularization. Although vascular enhanced permeability and retention can aid targeting, high interstitial fluid pressure and dense extracellular matrix may hinder local penetration. Extravascular diffusivity depends upon nanoparticle size, surface modifications, and tissue vascularization. Gold nanoparticles functionalized with biologically-compatible layers may achieve improved uptake and distribution while enabling cytotoxicity through synergistic combination of chemotherapy and thermal ablation. Evaluation of nanoparticle uptake in vivo remains difficult, as detection methods are limited. We employ hyperspectral imaging of histology sections to analyze uptake and distribution of phosphatidylcholine-coated citrate gold nanoparticles (CGN) and silica-gold nanoshells (SGN) after tail-vein injection in mice bearing orthotopic pancreatic adenocarcinoma. For CGN, the liver and tumor showed 26.5±8.2 and 23.3±4.1 particles/100μm² within 10μm from the nearest source and few nanoparticles beyond 50μm, respectively. The spleen had 35.5±9.3 particles/100μm² within 10μm with penetration also limited to 50μm. For SGN, the liver showed 31.1±4.1 particles/100μm² within 10μm of the nearest source with penetration hindered beyond 30μm. The spleen and tumor showed uptake of 22.1±6.2 and 15.8±6.1 particles/100μm² within 10μm, respectively, with penetration similarly hindered. CGH average concentration (nanoparticles/μm²) was 1.09±0.14 in the liver, 0.74±0.12 in the spleen, and 0.43±0.07 in the tumor. SGN average concentration (nanoparticles/μm²) was 0.43±0.07 in the liver, 0.30±0.06 in the spleen, and 0.20±0.04 in the tumor. Hyperspectral imaging of histology sections enables analysis of phosphatidylcholine-coated gold-based nanoparticles in pancreatic tumors with the goal to improve nanotherapeutic efficacy.     

Seasonal Rates of Methane Oxidation in Anoxic Marine Sediments

Methane concentrations and rates of methane oxidation were measured in intact sediment cores from an inshore marine sediment at Jutland, Denmark. The rates of methane oxidation, determined by the appearance of ¹⁴CO₂ from injected ¹⁴CH₄, varied with sediment depth and season. Most methane oxidation was anoxic, but oxygen may have contributed to methane oxidation at the sediment surface. Cumulative rates (0- to 12-cm depth) for methane oxidation at Kysing Fjord were 3.34, 3.48, 8.60, and 17.04 μmol m⁻² day⁻¹ for April (4°C), May (13°C), July (17°C), and August (21°C), respectively. If all of the methane was oxidized by sulfate, it would account for only 0.01 to 0.06% of the sulfate reduction. The data indicate that methane was produced, in addition to being oxidized, in the 0- to 18-cm sediment stratum.     

Preferential secretion of R-type alpha-amylase molecules in rice seed scutellum at high temperatures

Exposure of fresh scutella excised from 4-day-old rice seedlings to higher temperatures, (40-42°C), drastically reduced the biosynthesis of α-amylase as determined by the incorporation of [³⁵S]methionine into the immunoprecipitable product. However, the intracellular transport and extracellular secretion of the enzyme molecules were enhanced at high temperatures, indicating that the biosynthesis and secretion of α-amylase are distinguishable in their temperature dependency. At the higher temperature regime (40°C), the complex-type α-amylase isoform, resistant to hydrolytic digestion by endo-β-N-acetylglucosaminidase H (Endo-β-H) was predominantly secreted, whereas at lower temperatures (15°C), the isoform susceptible to Endo-β-H attack was the major molecular form secreted.     

Critical Behaviour in DOPC/DPPC/Cholesterol Mixtures: Static 2H NMR Line Shapes Near the Critical Point

Static ²H NMR spectroscopy is used to study the critical behavior of mixtures of 1,2-dioleoyl-phosphatidylcholine/1,2-dipalmitoyl-phosphatidylcholine (DPPC)/cholesterol in molar proportion 37.5:37.5:25 using either chain perdeuterated DPPC-d₆₂ or chain methyl deuterated DPPC-d₆. The temperature dependence of the first moment of the ²H spectrum of the sample made with DPPC-d₆₂ and of the quadrupolar splittings of the chain-methyl-labeled DPPC-d₆ sample are directly related to the temperature dependence of the critical order parameter η, which scales as [(T_c?T)/T_c]^β_c near the critical temperature. Analysis of the data reveals that for the chain perdeuterated sample, the value of T_c is 301.51 ± 0.1 K, and that of the critical exponent, β_c = 0.391 ± 0.02. The line shape analysis of the methyl labeled (d₆) sample gives T_c = 303.74 ± 0.07 K and β_c = 0.338 ± 0.009. These values obtained for β_c are in good agreement with the predictions of a three-dimensional Ising model. The difference in critical temperature between the two samples having nominally the same molar composition arises because of the lowering of the phase transition temperature that occurs due to the perdeuteration of the DPPC.     

Kinetics and thermodynamics of activation by pretreatment with guanosine 5′-[β-imido]triphosphate of smooth-muscle adenylate cyclase

Catalytic subunits (C) of uterine smooth-muscle adenylate cyclase were activated (C*) by incubating the enzyme with the GTP analogue guanosine 5′-[βγ-imido]triphosphate (p[NH]ppG), followed by treatment with GTP and washing at 2°C. Activation (C→C*) proceeded in a time- and temperature-dependent manner as disclosed by subsequent assay of the pretreated particles at 37°C. The properties of the activated subunits were a function of the pretreatment temperature and not those of the enzyme assay performed at 37°C. Over the range 6–24°C, activation by pretreatment with p[NH]ppG followed simple Michaelis–Menten kinetics, and increase in temperature increased the concentration of catalytic subunits in the C* state and decreased K_m for the guanosine nucleotide. Characterization of the temperature-dependent effects of pretreatment with p[NH]ppG suggested that activation of the catalytic subunit at the temperature in situ (37°C) was moderately endergonic (ΔH⁰ ~8kJ·mol⁻¹) and accompanied by an increase in entropy (ΔS⁰ ~146J·mol⁻¹·K⁻¹). The β-adrenergic catecholamine receptor, reflected by isoproterenol's effect on activation by pretreatment with p[NH]ppG, increased the concentration of catalytic subunits in the C* state but had an insignificant (P>0.05) effect on the K_m at every temperature. This result suggested that formation of the receptor–hormone complex produced an increase in the first-order rate constant without an appreciable effect on the actual catalytic-subunit activation step. The primary function of the β-adrenergic catecholamine receptor under these conditions appeared to be regulation of the concentration of activation sites available for binding of p[NH]ppG.