共查询到20条相似文献,搜索用时 15 毫秒
1.
Gefen A 《Journal of biomechanics》2011,44(1):206-8; discussion 208-9
2.
Florent Mazel 《Molecular ecology》2019,28(9):2119-2121
At high altitude, the reduced availability of thermal energy and oxygen poses major challenges to organisms. Different species or populations have evolved similar solutions to these challenges, such as blood flow regulation in animals (Bouverot, 1985). Previous studies investigating such convergent adaptations have primarily looked at changes in host genomes (e.g., see Scheinfeldt & Tishkoff, 2010), but have rarely considered the potential role of the gut microbiome in mediating host adaptation. As gut microbes can indirectly regulate host blood pressure (Pluznick, 2014) and energy intake efficiency, it has been hypothesized that they could help maintain normal energy production and/or optimize nutritional assimilation in high‐altitude hypoxic environments (e.g., Li & Zhao, 2015). However, it has been hard to (a) show that there is a direct effect of altitude on the gut microbiota, because of the many potential confounding effects of altitude (e.g., diet is correlated to altitude, as well as to the microbiome) and to (b) understand the mechanisms by which the microbiota could mediate host hypoxic and thermoregulatory stresses. In this issue of Molecular Ecology, Suzuki, Martins, and Nachman (2018) show that, independently of diet, taxonomic composition and functions of mouse gut microbiota converge in independent high‐altitude environments and propose the intriguing hypothesis that some of these functional convergences might be beneficial to their host. 相似文献
3.
Evelyn M. Doyle Catherine T. Kelly William M. Fogarty 《Applied microbiology and biotechnology》1989,30(5):492-496
Summary An -amylase capable of producing exceptionally high levels of maltose (74%) from starch has been identified from a strain of Penicillium expansum. The enzyme is produced extracellularly and was purified to homogeneity by starch adsorption and Sephadex gel filtration chromatography. P. expansum -amylase has a pH optimum of 4.5 and is stable in the pH range of 3.6–6.0. Other properties include a temperature optimum of 60° C, a molecular weight of 69 000 and an isoelectric point of 3.9. The most outstanding feature of the P. expansum enzyme is its ability to yield 14% more maltose and 17.1% less maltotriose than a currently used commercial enzyme. This may be partly explained by the greater affinity of this new enzyme for maltotriose (K
m=0.76 mM) relative to the commerical enzyme, Fungamyl (K
m=2.9 mM). The enzyme reported here is unique among fungal -amylases in being able to produce such high levels of maltose and its physicochemical properties suggest that it has potential for commercial development. 相似文献
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Summary RNA genomes have been shown to mutate much more frequently than DNA genomes. It is generally assumed that this results in
rapid evolution of RNA viral proteins. Here, an alternative hypothesis is proposed that close cooperation between positive-strand
RNA viral proteins and those of the host cells required their coevolution, resulting in similar amino acid substitution rates.
Constraints on compatibility with cellular proteins should determine, at any time, the covarion sets in RNA viral proteins.
These ideas may be helpful in rationalizing the accumulating data on significant sequence similarities between proteins of
positive-strand RNA viruses infecting evolutionarily distant hosts as well as between viral and cellular proteins. 相似文献
6.
Does high nitrogen loading prevent clear‐water conditions in shallow lakes at moderately high phosphorus concentrations? 总被引:17,自引:1,他引:16
María A. González Sagrario Erik Jeppesen Joan Gomà Martin Søndergaard Jens Peder Jensen Torben Lauridsen Frank Landkildehus 《Freshwater Biology》2005,50(1):27-41
1. The effect of total nitrogen (TN) and phosphorus (TP) loading on trophic structure and water clarity was studied during summer in 24 field enclosures fixed in, and kept open to, the sediment in a shallow lake. The experiment involved a control treatment and five treatments to which nutrients were added: (i) high phosphorus, (ii) moderate nitrogen, (iii) high nitrogen, (iv) high phosphorus and moderate nitrogen and (v) high phosphorus and high nitrogen. To reduce zooplankton grazers, 1+ fish (Perca fluviatilis L.) were stocked in all enclosures at a density of 3.7 individuals m?2. 2. With the addition of phosphorus, chlorophyll a and the total biovolume of phytoplankton rose significantly at moderate and high nitrogen. Cyanobacteria or chlorophytes dominated in all enclosures to which we added phosphorus as well as in the high nitrogen treatment, while cryptophytes dominated in the moderate nitrogen enclosures and the controls. 3. At the end of the experiment, the biomass of the submerged macrophytes Elodea canadensis and Potamogeton sp. was significantly lower in the dual treatments (TN, TP) than in single nutrient treatments and controls and the water clarity declined. The shift to a turbid state with low plant coverage occurred at TN >2 mg N L?1 and TP >0.13–0.2 mg P L?1. These results concur with a survey of Danish shallow lakes, showing that high macrophyte coverage occurred only when summer mean TN was below 2 mg N L?1, irrespective of the concentration of TP, which ranged between 0.03 and 1.2 mg P L?1. 4. Zooplankton biomass and the zooplankton : phytoplankton biomass ratio, and probably also the grazing pressure on phytoplankton, remained overall low in all treatments, reflecting the high fish abundance chosen for the experiment. We saw no response to nutrition addition in total zooplankton biomass, indicating that the loss of plants and a shift to the turbid state did not result from changes in zooplankton grazing. Shading by phytoplankton and periphyton was probably the key factor. 5. Nitrogen may play a far more important role than previously appreciated in the loss of submerged macrophytes at increased nutrient loading and for the delay in the re‐establishment of the nutrient loading reduction. We cannot yet specify, however, a threshold value for N that would cause a shift to a turbid state as it may vary with fish density and climatic conditions. However, the focus should be widened to use control of both N and P in the restoration of eutrophic shallow lakes. 相似文献
7.
Marianne Jegouic Valerij Ya. Grinberg André Guingant Thomas Haertlé 《Journal of Protein Chemistry》1996,15(6):501-509
Denaturation and aggregation of-lactalbumin at high pressure (up to 10 kbar, 1000 MPa) were studied by means of circular dichroism, gel-permeation chromatography, sodium dodecyl sulfate and gel electrophoresis. It was found that the unfolding of-lactalbumin at high pressure is reversible even in basic pH and at a protein concentration as large as 10%. In these conditions only a negligible fraction of the protein is denatured irreversibly and aggregates. The rate of aggregation of-lactalbumin at high pressure increases significantly in the presence of low-molecular reducing agents such as cysteine, 2-mercaptoethanol, and dithiothreitol. Maximal yield of-lactalbumin oligomerization (over 90%) was achieved in the presence of cysteine at the molar cysteine/protein ratioq=2 and atpH 8.5. Apparent molecular weight of the obtained oligomers was over 500 kDa. It was shown that the size distribution of oligomers can be modulated by varyingpH and reducing agent. The size distribution shifts in the direction of very large, poorly soluble particles whenpH decreases. Maximal content of the insoluble fraction (about 30%) can be reached at pH 5.5 when cysteine (q=2) is used as reducing agent. The oligomers of-lactalbumin are stabilized mainly by nonnative interchain disulfide bridges. Circular dichroism measurements point to an additional mechanism of cohesion of polypeptide chains in the oligomers, which is formation of intermolecular-sheets. 相似文献
8.
Ten men with uncomplicated essential hypertension (mean standing blood pressure 165/109 mm Hg) and 10 normal controls matched for age and weight were studied for the hypotensive potential of moderate exercise. Tests were conducted on a treadmill set to induce a steady heart rate of 120 beats/min and performed over five 10-minute periods separated by three minutes'' rest and finishing with 30 minutes'' sitting quietly in a chair.During exercise the mean systolic pressures were identical in the hypertensive patients and controls (175±SEM 5 mm Hg), the controls therefore sustaining an appreciably greater increase in pressure. During the 30-minute rest period after the tests both the control and hypertensive groups showed a significant and sustained fall in absolute systolic pressures as compared with pre-exercise values (p <0·001), the mean percentage reductions being 22% and 25% respectively.If a fall in blood pressure after exercise is maintained for four to 10 hours, then a “good walk” twice a day might be reasonable treatment for mild hypertension. Studies are continuing to determine the amount of exercise needed and the duration for which the reduction in blood pressure is maintained. 相似文献
9.
Summary In the presence of -glucosidase from almond, a 90% glucose solution gave four kind of -linked glucose-disaccharides. The yield increased as the concentration of glucose was increased and as the reaction temperature was raised. The maximum yield of disaccharides from 90% glucose solution was 40% at 55°C. 相似文献
10.
Rongjing Song Xi Wang Yiqing Mao Hui Li Zhixin Li Wei Xu Rong Wang Tingting Guo Ling Jin Xiaojing Zhang Yizhuang Zhang Na Zhou Ruobi Hu Jianwei Jia Zhen Lei David M. Irwin Gang Niu Huanran Tan 《Gene》2013
The effect of mouse resistin on hepatic insulin resistance in vivo and in vitro, and its possible molecular mechanism were examined. Focusing on liver glycogen metabolism and gluconeogenesis, which are important parts of glucose metabolism, in primary cultures of rat hepatocytes we found that glycogen content was significantly lower (P < 0.05) after treatment with recombinant murine resistin only in the presence of insulin plus glucose stimulation. Protein levels of factors in the insulin signaling pathway involved in glycogen synthesis were examined by Western blot analysis, with the only significant change observed being the level of phosphorylated (at Ser 9) glycogen synthase kinase-3β (GSK-3β) (P < 0.001). No differences in the protein levels for the insulin receptor β (IRβ), insulin receptor substrates (IRS1 and IRS2), phosphatidylinositol 3-kinase (PI3K), protein kinase B (Akt) or their phosphorylated forms were observed between control and resistin treated primary rat hepatocytes. In a mouse model with high liver-specific expression of resistin, fasting blood glucose levels and liver glycogen content changed. Fasting blood glucose levels were significantly higher (P < 0.001) in the model mice, compared to the control mice, while the glycogen content of the liver tissue was about 60% of that of the control mice (P < 0.05). The gluconeogenic response was not altered between the experimental and control mice. The level of phosphorylated GSK-3β in the liver tissue was also decreased (P < 0.05) in the model mice, consistent with the results from the primary rat hepatocytes. Our results suggest that resistin reduces the levels of GSK-3β phosphorylated at Ser 9 leading to impaired hepatic insulin action in primary rat hepatocytes and in a mouse model with high liver-specific expression of resistin. 相似文献
11.
The paradox high zooplankton biomass-low vegetal particulate organic matter in high turbidity zones: What way for energy transfer? 总被引:1,自引:0,他引:1
Valérie David Benoît Sautour Pierre Chardy 《Journal of experimental marine biology and ecology》2006,333(2):202-218
Estuarine ecosystems are characterized by high zooplanktonic biomasses, essentially constituted by copepods and mysids whose nutritional requirements are mainly provided by phytoplankton, an easily available carbon form. The Gironde estuary is characterized by high turbidities which limit light penetration in the water column and therefore primary production. Consequently, primary production is low and its availability for higher trophic level is very limited. The main goal of this study was to characterize the total vegetal particulate organic matter (POM) in high turbidity zones of the Gironde estuary during summer (a critical period characterized by high heterotrophic bacterial degradation and high zooplanktonic biomasses) and to analyse its utilization by zooplankton, using prey/predator experiments and trophic biomarkers (fatty acids). The specific goals were to define (i) how vegetal POM was exploited by the different zooplanktonic groups (protozoa, copepods and mysids) and (ii) which alternative preys could be used when vegetal POM was not sufficient to ensure their nutritional requirements.Chlorophyll biomass was very low in the MTZ during summer 2002 (0.48 ± 0.03 mg m− 3). Total zooplankton grazing was low (19% d− 1) probably due to a large contribution of detritus originating from terrestrial plants in vegetal POM compared to phytoplankton. The highest grazing pressure was exercised by the mysid Mesopodopsis slabberi due to its high abundances and by its almost entirely herbivorous diet (phytoplankton and small terrestrial detritus). Grazing rates (19.7 ± 4.2 and 9.6 μgC cop− 1 d− 1 for juveniles and adults, respectively) seemed to be sufficient to satisfy their daily carbon requirement. Grazing rate of the copepod Eurytemora affinis (139 ngC cop− 1 d− 1) seemed to be insufficient to cover its nutritional requirements and the copepods probably needed to complete a great part of their diet from protozoa. Grazing rates of the mysid Neomysis integer (24.7 ± 0.01 and 20.89 ± 8.45 μgC cop− 1 d− 1 for juveniles and adults, respectively) were higher than those of M. slabberi when feeding only on phytoplankton. However, when other preys were introduced in its environment, N. integer only fed on the copepod E. affinis with a preference for nauplii. The study revealed the great importance of protozoa and bacteria in the trophic transfers between vegetal POM and zooplankton in the MTZ during summer, despite the low protozoa grazing pressure on vegetal POM (3.1%). The detritic food chain probably implies various trophic transfers with little direct relationships between vegetal POM and zooplankton. 相似文献
12.
Summary Several inorganic and organic coagulating-flocculating agents were tried in various combinations for the clarification of broth having very high -amylase enzyme activity. Combination of calcium chloride, sodium hydroxide, ferrous sulphate and cationic polyacrylamide was found to give the optimum performance. 相似文献
13.
Recently, increasing evidence has linked high cholesterol to the pathogenesis of Alzheimer’s disease (AD), suggesting that
cholesterol may be a target for developing new compounds to prevent or treat AD. Plant sterols, a group of sterols enriched
in plant oils, nuts, and avocados, have the structure very similar to that of cholesterol, and have been widely used to reduce
blood cholesterol. Due to their cholesterol-lowering property, plant sterols such as β-sitosterol may also influence cholesterol-depending
functions including its role in AD development. Using human platelets, a type of peripheral blood cells containing the most
circulating amyloid precursor protein (APP), this study investigated the effect of β-sitosterol on high cholesterol-induced
secretion of β amyloid protein (Aβ). It was found that β-sitosterol effectively inhibited high cholesterol-driven platelet
Aβ release. In addition, β-sitosterol prevented high cholesterol-induced increase of activities of β- and γ-secretase, two
APP cleaving enzymes to generate Aβ. Additional experiments showed that high cholesterol up-regulated lipid raft cholesterol.
This effect of cholesterol could be suppressed by β-sitosterol. These findings suggest that β-sitosterol is able to inhibit
high cholesterol-induced Aβ release probably through maintenance of membrane cholesterol homeostasis. Given that dietary plant
sterols have the potential of penetrating the blood–brain barrier (BBB), these data suggest that plant sterols such as β-sitosterol
may be useful in AD prevention. 相似文献
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HENGHENRYHQ XIAOMEISHI 《Cell research》1997,7(1):119-124
Fluorescentinsituhybridization(FISH)methodologyisoneofthemostpowerfulandversatileexperimentalsystemsforcurrentbiology.Itbridgesthemolecularbiologyandcytologybyprovidingdirectandpreciseresearchtoolsforgenemapping,chromosomalstructurestudyandgenomeanalysis[1].OnemajorbreakthroughforFISHanalysis,istheintroductionoftheconceptandmethodologiesofhighresolutionfiberFISH[2,3].ByFISHdetectingonreleased,lesscondensed,andlinearizedchromatinorDNAfibers,theultrahighresolutionmappingdatacanbegenerate… 相似文献
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Rebecca J. Oakey Thad A. Howard Philip M. Hogarth Kenzaburo Tani Michael F. Seldin 《Immunogenetics》1992,35(4):279-282
Address correspondence and offprint requests to: M. F. Seldin. 相似文献
18.
We tested the fertilization insurance hypothesis of human twinning, which suggests that twin births should be seen as an unadaptive consequence of polyovulation compensating for high spontaneous abortion rates in humans. Females with high incidence of polyovulation were predicted to benefit by becoming pregnant more rapidly and by having a higher likelihood of successful pregnancy than other females. As a disadvantage, polyovulating mothers should be more prone to presumably maladaptive twin deliveries. We studied birth intervals of twin and singleton mothers living in pre-industrial Finland by using demographic records of local churches. The analysis revealed that, contrary to the prediction of the fertilization insurance hypothesis, polyovulating females did not display shorter intervals between deliveries. Therefore, if the tendency towards polyovulation and therefore occasional twin births in humans is adaptive and maintained by natural selection, other benefits should be evident. 相似文献
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James WH 《Teratology》2002,66(2):59; author reply 60
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An evolutionary war is being played out between the bat, which uses ultrasonic calls to locate insect prey, and the moth, which uses microscale ears to listen for the approaching bat. While the highest known frequency of bat echolocation calls is 212 kHz, the upper limit of moth hearing is considered much lower. Here, we show that the greater wax moth, Galleria mellonella, is capable of hearing ultrasonic frequencies approaching 300 kHz; the highest frequency sensitivity of any animal. With auditory frequency sensitivity that is unprecedented in the animal kingdom, the greater wax moth is ready and armed for any echolocation call adaptations made by the bat in the on-going bat–moth evolutionary war. 相似文献