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51.
Shlomo Nir Nejat Düzgünes Maria C. Pedroso De Lima Dick Hoekstra 《Cell biochemistry and biophysics》1990,17(2):181-201
The fusion of viruses with cells and liposomes is reviewed with focus on the analysis of the final extents and kinetics of
fusion.Influenza virus andSendai virus exhibit 100% of fusion capacity with cells at pH 5 and pH 7.5, respectively. On the other hand, there may be in certain
cases, a limit on the number of virions that can fuse with a single cell, that is significantly below the limit on binding.
It still remains to be resolved whether this limit reflects a limited number of possible fusion sites, or a saturation limit
on the amount of viral glycoproteins that can be incorporated in the cellular membrane, like the case of virus fusion with
pure phospholipid vesicles, in which the fusion products were shown to consist of a single virus and several liposomes. Both
viruses demonstrate incomplete fusion activity towards liposomes of a variety of compositions. In the case ofSendai virus, fusion inactive virions bind essentially irreversibly to liposomes. Yet, preliminary results revealed that such bound,
unfused virions can be released by sucrose gradient centrifugation. The separated unfused virions subsequently fuse when incubated
with a “fresh” batch of liposomes. We conclude, therefore, that the fraction of initially bound unfused virions does not consist
of dective particles, but rather of particles bound to liposomes via “inactive” sites.
Details of the low pH inactivation of fusion capacity ofinfluenza virus towards cells and liposomes are presented. This inactivation is caused by protonation and exposure of the hydrophobic
segment of HA2, and affects primarily the fusion rate constants. Some degree of inactivation also occurs when virions are bound to cellular
membranes. 相似文献
52.
We investigated the influence of mesohabitats on fish communities and on attributes of a multimetric index of fish integrity in the River Meuse basin. Three consecutive 150 m sectors in a Meuse tributary (Ourthe, Belgium), each divided in two or three sub-sections presenting various percentages of mesohabitats (riffles, runs and pools), were sampled by electrofishing. In each sub-section, relative and absolute biomasses of each fish species were estimated. The presence of limnophilic cyprinids was inversely correlated (r
2 = 0.70 and 0.56 for absolute and relative biomass, respectively) with the percentage of riffles. Salmonids preferred runs and their absolute biomass was highly dependent (r
2 = 0.71) on the proportion of this mesohabitat, whereas biomass of limnophilic cyprinids was highly correlated (r
2 = 0.75 and r
2 = 0.82 for absolute and relative biomass, respectively) with pools. A positive correlation (r
2 = 0.58) was established between relative biomass of predators and the percentage of this mesohabitat. An IBI was calculated for the three sectors on the basis of results from the entire Meuse catchment. Scores of most metrics showed low variation among sectors but values of two metrics (% of individuals as tolerant, % of individuals as ubiquitous spawners) were greatest in sector 2, where pools predominated. Further, the lowest IBI score (51/65, integrity class: fair to good) was recorded in sector 2 where pools dominated, while sector 1 (where runs dominated) obtained the highest score (63/65, integrity class: excellent). Sector 3 which has a balanced proportion of riffles and runs obtained an intermediate score (57/65). Considering the response of IBI to the natural variation of mesohabitat proportions, it appears that an accurate sampling requires the prospection of a variety of mesohabitats (with a majority of runs) for the evaluation of river quality. 相似文献
53.
Experiments in laboratory stream channels compared the behaviour of Deleatidium mayfly nymphs in the absence of fish with that in the presence of either native common river galaxias (Galaxias vulgaris Stokell) or introduced brown trout (Salmo trutta L.). Galaxias present similar predation risks to prey during day and night but are more active at night. Whereas, trout present a higher predation risk during the day. Deleatidium maintained a fixed nocturnal drift periodicity that is characteristic of streams containing visually feeding fish regardless of the nature of the predation regime presented in the laboratory. However, the number on the substratum surface, and therefore able to graze algae, was lower when fish were present than when they were absent. The number was lower during the day in the presence of trout, when they present the highest predation risk, and lower during the night compared to the day in trials with galaxias when galaxias activity disturbs Deleatidium from the substratum. Increases in the probability of Deleatidium leaving a patch, reductions in the proportion of mayflies on high quality patches and reductions in the distance travelled from refuge also reflected variations in the predation regime. Similar differences in positioning were observed under the same predation regimes in in situ channels in the Shag River and these were associated with differences in algal biomass. Algal ash-free dry mass (AFDM) and chlorophyll a (chl a) were higher on the tops of cobbles when fish were present. Fish also affected the biomass and the distribution of algae on cobbles as AFDM and chl a were higher on the sides of cobbles from channels with trout compared to those with galaxias. Changes in grazing behaviour, caused by predator avoidance, are likely to have been responsible for differences in algal biomass because no significant differences were detected between treatments in the biomass of Deleatidium or of total invertebrates. 相似文献
54.
We present here microwave-based modifications of standard protein assays that dramatically reduce the time required to determine
protein concentrations. Typical protein determinations involve incubation times ranging from 15–60 min. Microwave irradiation
of specimens reduces this time requirement to 10–20 s without compromising accuracy or reliability. The remarkable speed with
which protein determinations may be carried out using microwave enhancement greatly simplifies general laboratory procedures
that depend on the estimation of protein concentrations.
An erratum to this article is available at . 相似文献
55.
56.
Angelo De Milito Marinunzia Catucci Francesco Iannelli Laura Romano Maurizio Zazzi Pier Egisto Valensin 《Molecular biotechnology》1995,3(2):166-169
A reliable selective PCR procedure that combines the use of additionally mutated primers with the specificity-enhancing properties
of a commercial preparation (Perfect Match, Stratagene) is described. The human immunodeficiency virus type 1pol gene point mutations known to confer in vitro resistance to azidothymidine were examined as a model for optimization of the
assay. The usual strategy of deliberately introducing an additional mismatch 1 residue from the 3′ end in the wild-type and
mutant primers did not allow reproducible discrimination between wild-type and mutant target sequences. Addition of minimal
amounts of Perfect Match to the same PCR mixtures resulted in a significantly enlarged range of selective annealing temperatures,
providing a valuable and cost-effective means for reliable detection of known mutations by selectivePCR. 相似文献
57.
After considering the need for quality control in NAA, the concept of quality in NAA procedures themselves is discussed, and
some important factors identified. Two approaches to improve quality are then described in more detail. The first concerns
the unique ability of NAA using different isotopic reactions and different modes (INAA/RNAA) to provide independent data sets
in the same laboratory, thus allowing internal validation or crosschecking. The second discusses the need for chemical yield
measurements in RNAA and the advantages of the radioisotopic tracer technique. Some recent advances and further possibilities
for this use of tracers are listed. 相似文献
58.
Zagrodzki Paweł Mietelski Jerzy W. Krośniak Mirosław Petelenz Barbara 《Biological trace element research》1994,(1):273-277
The aim of this work was to check whether the stable cesium content in forest litter affects the value of radiocesium from
litter-to-mushroom transfer factorTf or not. Total cesium in litter, measured by AAS, varied from 0.1–2.7 μg/g. These data, combined with earlier results for
mushrooms, showed no simple correlation forTf. More complex relationships provided very high correlation coefficients, but their validity needs further investigation. 相似文献
59.
Vanadium was determined by radiochemical neutron activation analysis (RNAA) with proven accuracy in urine of workers occupationally
exposed to vanadium-rich dust in a vanadium pentoxide production plant, and values in the range of 3.02–762 ng/mL (median
33.0 ng/mL) were found. In a control group consisting of administrative workers of the plant, urinary vanadium levels were
found in the range of 1.05–53.4 ng/mL (median 2.53 ng/mL), whereas in an another control group of occupationally nonexposed
persons, these values amounted to 0.066–0.489 ng/mL (median 0.212 ng/mL).
Accuracy of the results was tested by analysis of reference material IAEA A-13 Animal Blood and NIST SRM-1515 Apple Leaves,
and very good agreement was found with literature and the NIST certified values, respectively. Unlike urine, no significant
differences were found for cystine levels in fingernails and hair of exposed and control persons. 相似文献
60.