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241.
St rker T. Moe Kurt I. Draget Gudmund Skj k-Br k Olav Simdsr d 《Carbohydrate polymers》1992,19(4):279-284
The temperature dependence of the elastic modulus for alginate gels was studied using two different gel systems: covalently crosslinked Na-alginate gels and in-situ prepared Ca-alginate gels. The modulus of physically crosslinked gels showed a complex behaviour. The temperature coefficient of the modulus of covalently crosslink gels changed from positive for the lowest crosslinked gels to negative for the highest crosslinked gels. This suggests a change from rubberlike to enthalpy-driven elasticity with an increasing degree of crosslinking for these gel networks. 相似文献
242.
Isolation and characterization of brush border membrane vesicles from pig small intestine 总被引:2,自引:0,他引:2
A J Moe M J Jackson 《Comparative biochemistry and physiology. A, Comparative physiology》1987,88(3):511-517
1. Brush border membrane vesicles (BBMV) were isolated from swine mid-intestine by a MgCl2 precipitation and sucrose density gradient centrifugation. 2. Transport of D-glucose and L-alanine were Na+-stimulated and into an osmotically sensitive space. 3. Estimates of kinetic parameters for Na+-dependent D-glucose transport were: apparent Kt = 1.8 mM and Jmax = 16.8 nmol/mg protein/min. 4. Results of experiments with the delta pH sensitive fluorescent probe 9-aminoacridine indicated independent mechanisms for Na+-dependent glucose transport and Na+/H+ exchange. 5. This study demonstrates that pig BBMV provide a useful model for investigating intestinal membrane transport. 相似文献
243.
Four adult Norwegian Red cows were employed in an experiment designed to study the kinetics of lactose. The cows were given 50 g or 60 g of lactose by rapid intravenous injection of a 10 % lactose solution. Blood samples were taken at different intervals after injection, and lactose concentrations in the samples determined by an enzymatic/spectrophotometric method. The mean half-time for lactose elimination was 85.7 min, and for distribution 8.4 min. The mean apparent volume of distribution was calculated to be 0.189 1/kg, and total body clearance 1.55 ml min−1 kg−1. There was evidence to suggest that lactose mainly is eliminated renally from its distribution volume by glomerular filtration in the cow. 相似文献
244.
245.
The application of gibberellins (GA) reduces the difference in stem elongation observed under a low day (DT) and high night
temperature (NT) combination (negative DIF) compared with the opposite regime, a high DT/low NT (positive DIF). The aim of
this work was to investigate possible thermoperiodic effects on GA metabolism and tissue sensitivity to GA by comparing the
response to exogenously applied GA (in particular, GA1 and GA3) in pea plants (Pisum sativum cv. Torsdag) grown under contrasting DIF. Control plants not treated with growth inhibitors or additional GA were 38% shorter
under negative (DT/NT 13/21°C) than positive DIF (DT/NT 21/13°C) because of shorter internodes. Additional GA1 or GA3 decreased the difference between positive and negative DIF. In pea plants dwarfed with paclobutrazol, which inhibits GA biosynthesis
at an early step, the response to GA1 was reduced more strongly by negative compared with positive DIF than the response to GA3. The induced stem elongation by GA19 and GA20 did not deviate significantly from the response to GA1. Plants treated with prohexadione-calcium, an inhibitor of both the production and the inactivation of GA1, grew equally tall under the two temperature regimes in response to both GA1 and GA3. We hypothesize that the reduced response to GA1 compared with GA3 in paclobutrazol-treated plants grown under negative DIF is caused by a higher rate of 2β-hydroxylation of GA1 into GA8 under negative than positive DIF. This contributes to lower levels of GA1 and consequently shorter stems and internodes in pea plants grown under negative than positive DIF. Differences in tissue
sensitivity to GA alone cannot account for this specific thermoperiodic effect on stem elongation.
Received May 28, 1998; accepted May 29, 1998 相似文献
246.
Mechanism of regulation of group IVA phospholipase A2 activity by Ser727 phosphorylation 总被引:1,自引:0,他引:1
Tian W Wijewickrama GT Kim JH Das S Tun MP Gokhale N Jung JW Kim KP Cho W 《The Journal of biological chemistry》2008,283(7):3960-3971
Although group IVA cytosolic phospholipase A(2) (cPLA(2)alpha) has been reported to be phosphorylated at multiple Ser residues, the mechanisms by which phosphorylation at different sites regulates cPLA(2)alpha activities are not fully understood. To explore the possibility that phosphorylation of Ser(727) modulates cellular protein-protein interactions, we measured the effect of Ser(727) mutations on the interaction of cPLA(2)alpha with a reported cPLA(2)alpha-binding protein, p11. In vitro activity assays and membrane binding measurements by surface plasmon resonance analysis showed that a heterotetramer (A2t) of p11 and annexin A2, but not p11 or annexin A2 alone, directly binds cPLA(2)alpha via Ser(727), which keeps the enzyme from binding the membrane and catalyzing the phospholipid hydrolysis. Phosphorylation of Ser(727) disrupts this inhibitory cPLA(2)alpha-A2t interaction, thereby activating cPLA(2)alpha. Subcellular translocation and activity measurements in HEK293 cells cotransfected with cPLA(2)alpha and p11 also showed that p11, in the form of A2t, inhibits cPLA(2)alpha by the same mechanism and that phosphorylation of Ser(727) activates cPLA(2)alpha by interfering with the inhibitory cPLA(2)alpha-A2t interaction. Collectively, these studies provide new insight into the regulatory mechanism of cPLA(2)alpha through Ser(727) phosphorylation. 相似文献
247.
The present study was conduced at two sites (Tembien and Wukro) in the semi-arid region of Tigray in northern Ethiopia to investigate the seasonal dynamics in the chemical composition and dry matter digestibility of grass and browse species of exclosures. The browse species studied in Tembien and Wukro had a mean crude protein (CP) value of 166 and 117 g/kg dry matter (DM), respectively. The mean in vitro dry matter digestibility (IVDMD) coefficient and predicted metabolizable energy (ME) density of the browse species were 0.72 and 9.83 MJ/kg DM, respectively at Tembien, 0.62 and 8.38 MJ/kg DM, respectively, at Wukro. Neutral detergent fibre (NDF) and acid detergent fibre (ADF) values of the browse species varied from 192 to 437 and 127 to 391 g/kg DM, respectively. Acid detergent lignin (ADL) values ranged from 36 to 190 g/kg DM. The mean CP of the grass species in Tembien and Wukro during the long rainy season was 76 and 73 g/kg DM, respectively and values declined below a critical maintenance level during the dry and short rain seasons. Mean IVDMD and ME values for the two sites were 0.41 and 0.47, and 5.38 and 6.11 MJ/kg DM, respectively. The NDF, ADF, and lignin values of the grass species were generally above 700, 400, and 70 g/kg DM, respectively. The CP, IVDMD and ME values of the mixed grass samples differed (P<0.05) among harvesting months and values ranged from 20 to 103 g/kg DM, 0.47 to 0.72 MJ/kg DM, and 6.16 to 9.91 MJ/kg DM, respectively. The browse species could be used as useful dry season protein supplements to the N deficient native grass species. Especial emphasis should be given to propagate Maerua angolensis and Cadaba farinosa at community nursery sites. Harvesting in September, rather than the current extended harvest period that took place in October and November, can considerably improve the feeding value of native grass hay for smallholder ruminant production systems. 相似文献
248.
Variations in species richness and diversity at a local scale are affected by a number of complex and interacting variables,
including both natural environmental factors and human-made changes to the local environment. Here we identified the most
important determinants of woody species richness and diversity at different growth stages (i.e. adult, sapling and seedling)
in a bamboo–deciduous forest in northeast Thailand. A total of 20 environmental and human disturbance variables were used
to determine the variation in species richness and diversity. In total, we identified 125 adult, 111 sapling (within fifty
20 × 20-m plots) and 89 seedling species (within one hundred and twenty 1 × 1-m subplots). Overall results from stepwise multiple
regression analyses showed that environmental variables were by far the most important in explaining the variation in species
richness and diversity. Forest structure (i.e. number of bamboo clumps and canopy cover) was important in determining the
adult species richness and diversity (R
2 = 0.48, 0.30, respectively), while topography (i.e. elevation) and human disturbance (i.e. number of tree stumps) were important
in determining the sapling species richness and diversity (R
2 = 0.55, 0.39, respectively). Seedling species richness and diversity were negatively related to soil phosphorus. Based on
our results, we suggest that the presence of bamboos should be incorporated in management strategies for maintaining woody
species richness and diversity in these forest ecosystems. Specifically, if bamboos cover the forest floor at high densities,
it may be necessary to actively control these species for successful tree establishment. 相似文献
249.
The purpose of this study was to investigate the need for and choice of stratification factors, and the effects of blinding
and placebo in a clinical experiment. Eighty dogs with canine hip dysplasia (CHD) were included in a randomized, placebo-controlled
and double blind clinical trial with stratified parallel group design, in which body weight and degree of CHD were used as
stratification factors. Thirty-eight dogs were allocated to gold bead implantation and 42 to placebo. After six months, 33
of the 42 placebo-treated dogs received gold bead implantation in an open study lasting a further 18 months. The main outcome
variable in the study was change in pain signs of CHD as assessed by the owner. No significant difference in the main outcome
variable, regardless of the treatment given, could be detected in the two chosen stratification factors. The only factor to
influence the main outcome variable significantly was age. The blinding procedure used in the study, in which 60% of the owners
correctly guessed the treatment given, was found sufficient. Of those who guessed the treatment erroneously, 88% believed
the treatment given was gold bead implantation. The treatment efficacy after six months in the blinded treatment group was
found to be significantly larger compared to the efficacy obtained in the open study. A significant placebo effect was therefore
detected. Conclusion and Clinical Relevance: The age of the dogs influenced the outcome of the CHD treatment, and is recommended
as a stratification factor. A significant placebo effect has to be expected and an optimal blinding procedure is necessary
in similar clinical studies. 相似文献
250.
Strong positive effects of termites on savanna bird abundance and diversity are amplified by large herbivore exclusion
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Stein R. Moe Katrine Eldegard Ole Tobias Rannestad Paul Okullo Ommund Lindtjørn Ole Gunnar Støen Svein Dale 《Ecology and evolution》2017,7(23):10079-10088
Vast areas of the African savanna landscapes are characterized by tree‐covered Macrotermes termite mounds embedded within a relatively open savanna matrix. In concert with termites, large herbivores are important determinants of savanna woody vegetation cover. The relative cover of woody species has considerable effects on savanna function. Despite the potentially important ecological relationships between termite mounds, woody plants, large herbivores, and birds, these associations have previously received surprisingly little attention. We experimentally studied the effects of termites and large herbivores on the avian community in Lake Mburo National Park, Uganda, where woody vegetation is essentially limited to termite mounds. Our experiment comprised of four treatments in nine replicates; unfenced termite mounds, fenced mounds (excluding large mammals), unfenced adjacent savanna, and fenced savanna. We recorded species identity, abundance, and behavior of all birds observed on these plots over a two‐month period, from late dry until wet season. Birds used termite mounds almost exclusively, with only 3.5% of observations occurring in the treeless intermound savanna matrix. Mean abundance and species richness of birds doubled on fenced (large herbivores excluded) compared to unfenced mounds. Feeding behavior increased when large mammals were excluded from mounds, both in absolute number of observed individuals, and relative to other behaviors. This study documents the fundamental positive impact of Macrotermes termites on bird abundance and diversity in an African savanna. Birds play crucial functional roles in savanna ecosystems, for example, by dispersing fruits or regulating herbivorous insect populations. Thus, the role of birds in savanna dynamics depends on the distribution and abundance of termite mounds. 相似文献