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71.
It is known that the negatively stained preparations of inner mitochondrial membrane display characteristic ∼9 nmF
1 (ATPase) knobs projecting from the matrix surface. Freeze-etch studies have reported the absence of such knobs from the “etched”
surface of the inner mitochondrial membranes. We have demonstrated their presence on the surface of SMP (submitochondrial
particles) prepared by freeze-drying for transmission electron microscopy. This identification has been substantiated by comparison
with the freeze-dried TU particles (trypsin-urea treated SMP) that are devoid ofF
1 (ATPase). It has been suggested that a layer of water molecules is strongly adsorbed to the surface of SMP and does not sublime
during normal freeze-“etching.” 相似文献
72.
D. Shaham I. Choshniak J. Rosenfeld C. Witenberg K. Thurau A. Shkolnik 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1994,164(2):112-117
When severely dehydrated Bedouin goats were allowed to drink to satiation their plasma arginine vasopressin concentration
immediately dropped from a value of 19.9±9.4 pmol·l-1 to 9.4±3.9 pmol·l-1 (P<0.05). It continued to drop further until a concentration of 1.8±2.9 pmol·l-1 was recorded, similar to that reported for goats allowed to drink freely. When the goats were shown the water but drinking
was denied, plasma arginine vasopressin immediately dropped to 11.7±4.0 pmol·l-1 (P<0.05) and further decreased to 10.0±4.8 pmol·l-1 5 min following their sighting the water. This level, however, was not sustained and 2 h after the initial drop the high
pre-trial concentration of plasma arginine vasopression was regained. Presumably, sighting of water by dehydrated goats induces
an abrupt drop in their plasma arginine vasopressin level even before drinking commences. When rehydrated, by introducing
water directly to the rumen, circumventing both the sensing of the water and the drinking proper, no immediate drop in the
plasma arginine vasopression concentration of the newly rehydrated goats was observed. A delayed drop in the plasma arginine
vasopressin levels took place slowly, concurrently with the drop in osmolality and concentration of Na+ in the plasma. It is suggested that sighting of water by dehydrated goats is involved in the modulation of plasma arginine
vasopressin. 相似文献
73.
74.
Long-column laboratory tests were performed to validate improvements to the MOFAT program for simulating LNAPL displacement and entrapment in response to a fluctuating water table. The long-column tests consisted of a fluctuating water table and its subsequent displacement and entrapment of an LNAPL. The modifications of MOFAT include a linear LNAPL trapping estimate and a new scaling technique for the inhibition portion of the fluctuation (water table rise). Improved prediction of the LNAPL trapping was obtained by assuming the amount of LNAPL that is trapped by a rising water table is proportional to the antecedent water content of the porous medium. The pressure-saturation relationship for the air-water drainage system was scaled to estimate the LNAPL-water and air-LNAPL drainage relationships. Scaled inhibition pressure-saturation relationships are improved by incorporating a correction for contact angle hysteresis and surface roughness. The incorporation of these changes into MOFAT led to noticable improvements in the numerical simulation of the experimental data. 相似文献
75.
State of the art and research needs for the impact category eutrophication are discussed. Eutrophication is a difficult impact
category because it includes emissions to both air and water — both subject to different environmental mechanisms — as well
as impacts occurring in different types of terrestrial and aquatic ecosystems. The possible fate processes are complex and
include transportation between different ecosystems. In some recent approaches, transportation modelling of air emissions
has been included. However, in general, the used characterisation methods do not integrate fate modelling, which is a limitation.
The definition of the impact indicator needs further research, too. The inclusion of other nutrients than those typically
considered should also be investigated. 相似文献
76.
Dickson Fenn 《FEBS letters》2008,582(30):4169-4175
Oxidation of guanine in DNA can lead to mutagenic lesions such as 7-hydro-8-oxoguanine (oG). Upon further oxidation, a more mutagenic lesion, spirominodihydantoin (Sp), can occur. In this study, nuclear magnetic resonance (NMR) investigations were performed to determine the structural features of DNA primer-template models with 5′-GG, 5′-G(oG), 5′-G(Sp) and 5′-T(Sp) templates, that mimic the situation in which the downstream G of the template has been oxidized to oG or hyperoxidized to Sp. Our results show that misalignment occurs only in the 5′-G(Sp) and 5′-T(Sp) templates, providing structural insights into the observed differences in mutagenicity of Sp and oG during DNA replication. 相似文献
77.
Previous work indicated that long-term exposure to elevated carbon dioxide levels can reduce hydraulic conductance in some species, but the basis of the response was not determined. In this study, hydraulic conductance was measured at concentrations of both 350 and 700 cm3 m–3 carbon dioxide for plants grown at both concentrations, to determine the reversibility of the response. In Zea mays and Amaranthus hypochondriacus , exposure to the higher carbon dioxide concentration for several hours reduced whole-plant transpiration rate by 22–40%, without any consistent change in leaf water potential, indicating reversible reductions in hydraulic conductance at elevated carbon dioxide levels. Hydraulic conductance in these species grown at both carbon dioxide concentrations responded similarly to measurement concentration of carbon dioxide, indicating that the response was reversible. In Glycine max , which in earlier work had shown a long-term decrease in hydraulic conductance at elevated carbon dioxide levels, and in Abutilon theophrasti , no short-term changes in hydraulic conductance with measurement concentration of carbon dioxide were found, despite lower transpiration rates at elevated carbon dioxide. In G. max and Medicago sativa , growth at high dew-point temperature reduced transpiration rate and decreased hydraulic conductance. The results indicate that both reversible and irreversible decreases in hydraulic conductance can occur at elevated carbon dioxide concentrations, and that both could be responses to reduced transpiration rate, rather than to carbon dioxide concentration itself. 相似文献
78.
The thermal stability of Candida rugosa (C. rugosa) lipase was investigated and compared in n-hexane, benzene, dibutyl-ether as well as [bmim]PF6 and [omim]PF6 ionic liquids and the effect of solvent polarity and water activity were evaluated. Deactivation of the enzyme followed a series-type kinetic model. First order deactivation rate constants and the ratios of specific activities were determined and the kinetics of deactivation were studied. Among the organic solvents, the best stability was observed in n-hexane with a half-life of 6.5?h at water activity of 0.51. In ionic liquids, however, even longer half lives were obtained, and the enzyme was stable in these solvents at 50°C. The highest half-life times were obtained in [bmim]PF6 (12.3?h) and [omim]PF6 (10.6?h). A direct correlation was found between solvent polarity and thermal stability since the higher the polarity of the solvent, the lower was the stability decrease at 50°C comparing to that at 30°C. 相似文献
79.
GERALDINE D. RYAN LISA EMILJANOWICZ SIMONE A. HÄRRI JONATHAN A. NEWMAN 《Ecological Entomology》2014,39(3):309-315
1. Elevated CO2 can alter plant physiology and morphology, and these changes are expected to impact diet quality for insect herbivores. While the plastic responses of insect herbivores have been well studied, less is known about the propensity of insects to adapt to such changes. Genetic variation in insect responses to elevated CO2 and genetic interactions between insects and their host plants may exist and provide the necessary raw material for adaptation. 2. We used clonal lines of Rhopalosiphum padi (L.) aphids to examine genotype‐specific responses to elevated CO2. We used the host plant Schedonorus arundinaceus (tall fescue; Schreb), which is capable of asexual reproduction, to investigate host plant genotype‐specific effects and possible host plant‐by‐insect genotype interactions. The abundance and density of three R. padi genotypes on three tall fescue genotypes under three concentrations of CO2 (ambient, 700, and 1000 ppm) in a controlled greenhouse environment were examined. 3. Aphid abundance decreased in the 700 ppm CO2 concentration, but increased in the 1000 ppm concentration relative to ambient. The effect of CO2 on aphid density was dependent on host plant genotype; the density of aphids in high CO2 decreased for two plant genotypes but was unchanged in one. No interaction between aphid genotype and elevated CO2 was found, nor did we find significant genotype‐by‐genotype interactions. 4. This study suggests that the density of R. padi aphids feeding on tall fescue may decrease under elevated CO2 for some plant genotypes. The likely impact of genotype‐specific responses on future changes in the genetic structure of plant and insect populations is discussed. 相似文献
80.