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31.
Summary Exchange isotherms of Cu2+
vs Zn2+-ions were performed on the cell wall of a fresh water alga,Nitella flexilis. The relevant thermodynamic parameters are calculated. The cell wall absorbs copper selectively. The selectivity is explained
by a stronger chelation of the cupric ion, due to the Jahn-Teller effect. The wall acts like a two-site model, based on the
nature of the ligands: a first group of aminesites reacts exothermically and a second of hydroxylic-carboxylic sites of lower
affinity, reacts endothermically. 相似文献
32.
Gale W. Rafter 《Biological trace element research》1982,4(2-3):191-197
Leukocytes incubated with Cu(II) showed a decrease in both glutathione reductase activity and reduced glutathione content.
The glucose 6-phosphate dehydrogenase activity under the same conditions was not affected. Serum albumin added to mixtures
prevented the loss of enzyme activity, whiled-penicillamine andl-histidine had little effect. Prior oxidation of the cell-reduced glutathione did not diminish the enzyme inhibitory action
of Cu(II). The amount of regeneration of reduced glutathione in leukocytes previously treated with diamide to oxidize their
reduced glutathione was a function of Cu(II) concentration in the media. No evidence was obtained that elevated serum ceruloplasmin
levels in rabbits, nor incubation of leukocytes in vitro with ceruloplasmin, affect leukocyte glutathione reductase activity.
It was proposed that the major mechanism by which copper affects glutathione metabolism in leukocytes is by inhibition of
glutathione reductase. 相似文献
33.
The antimutagenic effect of selenium as sodium selenite, sodium selenate, selenium dioxide, and seleno-methionine was studied
in the AmesSalmonella/microsome mutagenicity test using 7,12-dimethylbenz(a)anthracene (DMBA) and some of its metabolites. Selenium (20 ppm) as
sodium selenite reduced the number of histidine revertants on plates containing up to 100 μg DMBA/plate. Increasing concentrations
of selenium as sodium selenite, sodium selenate, and selenium dioxide up to 40 ppm Se progressively decreased the number of
revertants caused by 50 μg DMBA. DMBA and its metabolites 7-hydroxymethyl-12-methylbenz(a)anthracene, 12-hydroxymethyl-7-methylbenz(a)anthracene,
and 3-hydroxy-7,12-dimethylbenz(a)anthracene were mutagenic forSalmonella typhimurium TA100 in the presence of an S-9 mixture. Selenium supplementation as Na2SeO3 reduced the number of revertants induced by these metabolites to background levels. The antimutagenic effect of inorganic
selenium compounds cannot be explained by toxicity of selenium as determined by viability tests withSalmonella typhimurium TA100. Selenium supplementation in all forms examined, except sodium selenate, decreased the rate of spontaneous reversion.
Selenium as sodium selenate was slightly mutagenic at concentrations of 4 ppm or less. Higher concentration of Na2SeO4 inhibited the mutagenicity of DMBA. The present studies support the anticarcinogenic potential of selenium and indicate that
form and concentration are important factors in this trace element's efficacy. 相似文献
34.
Differentiation between the somatostatin inhibition and the post-somatostatin rebound observed on growth hormone secretion in vitro 总被引:1,自引:0,他引:1
A rebound in growth hormone secretion following somatostatin treatment has been shown in several systems where somatostatin suppresses secretion of the hormone. We have developed an in vitro system in which isolated and cultured pituitary cells were perfused after mild trypsinization. After washing, these cells retained their sensitivity and secreted growth hormone (GH) in response to physiological activators (norepinephrine, dopamine, serotonin) or inhibitors (somatostatin) as well as pharmacological activators (PGE2). The variation in GH secretion occurred within a minute after commencement of the infusion and was as rapidly reversible and repeatable minutes later. During somatostatin infusion the GH secretion was not totally suppressed (residual secretion (mean +/- S.D.) 34 +/- 7%). After the infusion a rapid rebound in GH secretion occurred, reaching levels in excess of the pretreatment value of 138 +/- 13%. This rebound effect occurred at doses higher than (10(-10)M) but not at lower doses, even when significant inhibition was observed. The inhibitory effect is of greater magnitude than the rebound effect (rebound = inhibition X 57 +/- 7% (mean +/- S.D.)). Furthermore, rebound was not enhanced by prolongation of somatostatin infusion. These latter results indicate that the rebound in secretion cannot be explained on the sole basis of storage of intracellular GH during somatostatin infusion and in fact suggest the involvement of a process of GH degradation and/or an inhibition of GH synthesis. 相似文献
35.
36.
Mtitchell J. S., Halton D. W. and Smyth J. D. 1978. Observations on the in vitro culture of Cotylurus erraticus (Trematoda: Strigeidae). International Journal for Parasitology8: 389–397. Cotylurus erraticus metacercariae obtained from around the heart of rainbow trout were excysted and grown in vitro and in vivo to egg-producing adults. For in vitro development, tissue culture media M199 or NCTC 135 was used, together with varying amounts of chicken serum. Worms grown in media containing the highest concentration of serum (80% per volume) showed the fastest rate of development, measured by the time taken for the first eggs to appear in the uterus. The testes, ovaries and vitellaria of these worms were comparable in structure and histochemistry with those of worms reared in gulls. Eggs were produced by worms in all media containing chicken serum, but the eggs had abnormal shells and failed to embryonate. 相似文献
37.
Yeongseon Park Yuseob Kim 《Evolution; international journal of organic evolution》2019,73(8):1564-1577
Temporally varying selection is known to maintain genetic polymorphism under certain restricted conditions. However, if part of a population can escape from selective pressure, a condition called the “storage effect” is produced, which greatly promotes balanced polymorphism. We investigate whether seasonally fluctuating selection can maintain polymorphism at multiple loci, if cyclically fluctuating selection is not acting on a subpopulation called a “refuge.” A phenotype with a seasonally oscillating optimum is determined by alleles at multiple sites, across which the effects of mutations on phenotype are distributed randomly. This model resulted in long‐term polymorphism at multiple sites, during which allele frequencies oscillate heavily, greatly increasing the level of nonneutral polymorphism. The level of polymorphism at linked neutral sites was either higher or lower than expected for unlinked neutral loci. Overall, these results suggest that for a protein‐coding sequence, the nonsynonymous‐to‐synonymous ratio of polymorphism may exceed one. In addition, under randomly perturbed environmental oscillation, different sets of sites may take turns harboring long‐term polymorphism, thus making trans‐species polymorphism (which has been predicted as a classical signature of balancing selection) less likely. 相似文献
38.
The applicability of theoretical group methods to studying complex physical and biological systems with the potential of self-organization was demonstrated. The problem of calculating climate sensitivity parameters taking into account the cyclone-anticyclone structure of the atmosphere optically dense in the infrared region is considered as an example. 相似文献
39.
It has been reported that flashing light enhances microalgal biomass productivity and overall photosynthetic efficiency. The
algal growth kinetics and oxygen production rates under flashing light with various flashing frequencies (5 Hz-37 kHz) were
compared with those under equivalent continuous light in photobioreactors. A positive flashing light effect was observed with
flashing frequencies over 1 kHz. The oxygen production rate under conditions of flashing light was slightly higher than that
under continuous light. The cells under the high frequency flashing light were also observed to be healthier than those under
continuous light, particularly at higher cell concentrations. When 37 kHz flashing light was applied to an LED-based photobioreactor,
the cell concentration was higher than that obtained under continuous light by about 20%. Flashing light may be a reasonable
solution to overcome mutual shading, particularly in high-density algal cultures. 相似文献
40.
Joan Thiesen Torben S. Christensen Thomas G. Kristensen Rikke D. Andersen Brit Brunoe Trine K. Gregersen Mikkel Thrane Bo P. Weidema 《The International Journal of Life Cycle Assessment》2008,13(2):104-114
Goal, Scope and Background Traditionally, comparative life cycle assessments (LCA) have not considered rebound effects, for instance in case of significant
price differences among the compared products. No justifications have been made for this delimitation in scope. This article
shows that price differences and the consequent effects of marginal consumer expenditure may influence the conclusions of
comparative LCA significantly. We also show that considerations about rebound effects of price differences can be included
in LCAs.
Methods The direct rebound effect of a price difference is marginal consumption. Based on statistical data on private consumption
in different income groups (Statistics Denmark 2005a, 2005b), the present article provides an estimate of how an average Danish
household will spend an additional 1 DKK for further consumer goods, when the household has gained money from choosing a cheaper
product alternative. The approach is to use marginal income changes and the following changes in consumption patterns as an
expression for marginal consumption. Secondly, the environmental impact potentials related to this marginal consumption are
estimated by the use of environmental impact intensity data from an IO-LCA database (Weidema et al. 2005). Finally, it is
discussed whether, and in which ways the conclusions of comparative LCAs can be affected by including the price difference
between product alternatives. This is elucidated in a case study of a comparative LCA screening of two different kinds of
Danish cheese products (Fricke et al. 2004).
Results Car purchase and driving, use and maintenance of dwelling, clothing purchase and insurance constitutes the largest percentages
of the marginal consumption. In a case study of two cheeses, the including the impact potentials related to the price difference
results in significant changes in the total impact potentials. Considering the relatively small price difference of the two
products, it is likely also to have a significant influence on the results of comparative LCAs more generally.
Discussion The influence of marginal consumption in comparative LCAs is relevant to consider in situations with large differences in
the price of the product alternatives being compared, and in situations with minor differences in the impact potentials related
to the alternatives. However, different uncertainties are linked to determining the pattern for marginal consumption and the
environmental impact potential related to this. These are first of all related to the method used, but also include inaccurate
data of consumption in households, aggregation and weighting of income groups, aggregation of product groups, estimation and
size of the price difference, and the general applicability of the results.
Conclusion Incorporating marginal consumption in consequential LCAs is possible in practice. In the case study used, including the rebound
effects of the price difference has a significant influence on the result of the comparative LCA, as the result for the impact
categories acidification and nutrient enrichment changes in favour of the expensive product.
Recommendations and Perspectives It is recommended that the rebound effects of price differences should be included more frequently in LCAs. In order to ensure
this, further research in marginal consumption and investment patterns and IO data for different countries or regions is required.
Furthermore, this study does not consider the economic distributional consequences of buying an expensive product instead
of a cheaper product (e.g. related to how the profit is spent by those who provided the product). It should also be noted,
that more expensive products not necessarily result in less consumption, as those who provided the product also will spend
the money they have earned from the sale. Ideally, these consequences should also be further investigated. Likewise, the development
of databases to include marginal consumption in PC-tools is needed. In general, considerations of marginal consumption would
favour expensive product alternatives, depending, however, on the type of consumer.
ESS-Submission Editor: Dr. David Hunkeler (david.hunkeler@aquaplustech.ch) 相似文献