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41.
The concentrations of copper, zinc and molybdenum were measured in samples of cattle liver from 10 slaughter-houses in Norway. A total of 335 samples were analysed. A clear accumulation of copper with age was found, the average copper level in the younger animals (≦ 3 years, n = 194) being 30 µg Cu/g liver wet weight, and in the older ones (> 3 years, n = 141) 59 µg Gu/g. The range in the copper values found was considerable, though significant differences between some of the districts were recorded. Copper concentrations were classified as low (≦10 µg Gu/g) in 9.6 % of the samples. Zinc showed no accumulation with age, nor were there any differences in zinc levels found in animals from different districts, the average level being 32 µg Zn/g liver wet weight. The picture was the same for molybdenum, no differences between age groups or districts being found. The average level was 1.0 µg Mo/g liver. There was no significant correlation between levels of copper, zinc or molybdenum.The supply of copper and zinc to cattle in Norway seems close to sufficient, but copper- and zinc-fortified mineral supplementation of cattle feed is still to be recommended. There seems to be no need for molybdenum supplementation in cattle. 相似文献
42.
The concentrations of copper, zinc and molybdenum were measured in liver samples from 21 normal slaughter pigs (average age about 6 months) and in 36 sows (average age about 2 years). The following mean values were found: Slaughter pigs: 15 ± 8 µg Cu/g, 45 ± 7 μg Zm/g and 1.0 ± 0.2 μg Mo/g wet weight; sows: 46 ± 70 μg Cu/g, 70 ± 26 μg Zn/g and 1.3 ± 0.3 μg Mo/g wet weight. The concentrations of all 3 elements were significantly higher in the sows than in the young pigs. There was no correlation between the concentrations of copper, zinc or molybdenum. The recorded copper levels in the slaughter pigs were in accordance with the levels of non-supplemented pigs given in the literature. The soluble hepatic copper- and zinc-binding proteins were separated into 3 different fractions by gel filtration. With increasing copper and zinc levels in the liver, a higher relative amount of these elements were found in the low molecular weight fraction. 相似文献
43.
Royo F Andersson G Bangyeekhun E Múzquiz JL Söderhäll K Cerenius L 《Veterinary microbiology》2004,104(1-2):103-112
Five Aphanomyces strains were isolated during suspected outbreaks of crayfish disease in Spain and Italy. Genetic and physiological evidence show that the strains isolated from the freshwater crayfish Procambarus clarkii and Pacifastacus leniusculus, do not fit into any previously identified group of Aphanomyces astaci and are not capable of killing crayfish following standardised experimental infection. RAPD-PCR and ITS sequencing analysis show a high degree of similarity between the new isolates, while they are clearly different from the A. astaci reference strains. They do, however, possess some properties, which are commonly associated with parasitic species such as repeated zoospore emergence and the lack of sexual reproduction. The five isolates share some physiological properties i.e. a high growth rate, and germination in response to nutrients and, in contrast to A. astaci, they do not express chitinase constitutively during growth or sporulation. Until their taxonomic status is fully elucidated we suggest that the new isolates be given the tentative species name Aphanomyces repetans. 相似文献
44.
45.
How do integral membrane proteins evolve in size and complexity? Using the small multidrug-resistance protein EmrE from Escherichia coli as a model, we experimentally demonstrated that the evolution of membrane proteins composed of two homologous but oppositely oriented domains can occur in a small number of steps: An original dual-topology protein evolves, through a gene-duplication event, to a heterodimer formed by two oppositely oriented monomers. This simple evolutionary pathway can explain the frequent occurrence of membrane proteins with an internal pseudo-two-fold symmetry axis in the plane of the membrane. 相似文献
46.
47.
The mechanism of voltage gating in K+ channels is controversial. The paddle model posits that highly charged voltage-sensor domains move relatively freely across the lipid bilayer in response to membrane depolarization; competing models picture the charged S4 voltage-sensor helix as being shielded from lipid contact by other parts of the protein. We measured the apparent free energy of membrane insertion of a K+-channel S4 helix into the endoplasmic reticulum membrane and conclude that S4 is poised very near the threshold of efficient bilayer insertion. Our results suggest that the paddle model is not inconsistent with the high charge content of S4. 相似文献
48.
Colwell RK Brehm G Cardelús CL Gilman AC Longino JT 《Science (New York, N.Y.)》2008,322(5899):258-261
Many studies suggest that global warming is driving species ranges poleward and toward higher elevations at temperate latitudes, but evidence for range shifts is scarce for the tropics, where the shallow latitudinal temperature gradient makes upslope shifts more likely than poleward shifts. Based on new data for plants and insects on an elevational transect in Costa Rica, we assess the potential for lowland biotic attrition, range-shift gaps, and mountaintop extinctions under projected warming. We conclude that tropical lowland biotas may face a level of net lowland biotic attrition without parallel at higher latitudes (where range shifts may be compensated for by species from lower latitudes) and that a high proportion of tropical species soon faces gaps between current and projected elevational ranges. 相似文献
49.
During the latter decades extensive fish kills have been observed in the mountainous areas of southernmost Norway. These kills have been attributed to the increased acidity of the river-water. The increased acidity is generally assumed to be caused by acid precipitation. However, the relationship between precipitation and runoff quality is very complex. The present paper is concerned with the relationship between chemical composition of simulated rain and that of runoff from bare granitic rock, partly covered by lichens. When supplying simulated rain with a pH value of approximately 5 the very first runoff had pH values between 4.1 and 4.3. However, the pH in the runoff increased rapidly and leveled out at values between 4.6 and 4.7. When supplying simulated rain with pH approximately 3.5, the pH in the first runoff varied between 3.8 and 3.6. The pH then gradually decreased to the same values as those in the simulated rain. Runoff from ‘rain’ with pH 4.3, obtained the same pH value as that of the ‘rain’. The pH of the runoff was dependent not only on the rain acidity, but also on its content of neutral salts. 相似文献
50.
Analysis of cod catch data from Icelandic groundfish surveys using generalized linear models 总被引:1,自引:0,他引:1
Catch data from the Icelandic groundfish surveys are analyzed using generalized linear models (GLM). The main goal is to test the effects of environmental variables on the expected cod catch and to distinguish between the gamma and log-normal distributions for the error structure. Only positive catch data are included in this work, i.e. only the positive part of a delta–gamma or delta–log-normal distribution is examined. The distributions are compared via a Kolmogorov–Smirnov goodness of fit test. Polynomials are used to describe the relationship between each environmental variable and the cod catch and their effects are tested within the GLM framework (a continuous model). Finally, an attempt is made to locate temperature fronts in the ocean by estimating the temperature gradient vector at each data point. The effect of the size of this gradient vector is then tested within in the GLM framework. A stratification model with only spatial and time effects explains 80% of the variation but that comes with a high cost of degrees of freedom. Most of the tested effects are found to be significant but the continuous model only captures 45% of the total variation. The size of the temperature gradient vector is found to be statistically significant though only a small portion of the variation in the data is explained by this term. 相似文献