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91.
Gordon C. K. Roberts 《Neurochemical research》1996,21(9):1117-1124
NMR spectroscopy has proved to be a valuable tool in the study of the interactions between enzymes and their substrates. The
kinds of structural and dynamic information which can be obtained are illustrated by studies of three enzymes involved in
drug metabolism. Cytochromes P450 play a crucial role in metabolism of a wide range of exogenous chemicals. NMR has been used to measure distances from the
haem iron of the cytochrome to protons of the bound substrate, leading to detailed structural models for the enzyme-substrate
complexes. The other two enzymes, chloramphenicol acetyltransferase and β-lactamase, are responsible for bacterial resistance
to specific antibiotics. In chloramphenicol acetyltransferase, NMR has been used to determine the conformation of coenzyme
A bound to the enzyme, while in the case of β-lactamase the pK of a specific lysine residue at the active site has been determined,
providing valuable information on the catalytic mechanism.
Special issue dedicated to Dr. Herman Bachelard. 相似文献
92.
Sulabha S. Keskar Sushama M. Gaikwad M.Islam Khan 《Enzyme and microbial technology》1996,18(8):602-604
Microbial α-mannosidases are used in the analysis of glycopeptides and the developmental regulation of lysosomal enzymes. This survey presents comparison of properties of this high molecular weight, oligomeric protein from a number of microbial sources. 相似文献
93.
P. J. den Besten C. A. Schmidt M. Ohm M. M. Ruys J. W. van Berghem C. van de Guchte 《Journal of Aquatic Ecosystem Stress and Recovery (Formerly Journal of Aquatic Ecosystem Health)》1995,4(4):257-270
The quality of sediment was assessed in 46 sites in the delta of the rivers Rhine and Meuse (The Netherlands) by means of physical-chemical analysis, field observations on the macrobenthic community structure, accumulation studies and bioassays using Chironomus riparius, Daphnia magna and Photobacterium phosphoreum. The results of chemical analyses were classified using national criteria for sediment quality. Results of field studies and bioassays were classified using criteria derived from research in reference areas or based on data from literature. Risk assessment was carried out according to the sediment quality triad and by means of multi criteria analysis (MCA). The Triad approach was used to demonstrate causal relations between effects on the macrozoobenthos community structure, effects demonstrated in bioassays and sediment pollution. This was done by making a comparison of sediment contamination levels with toxicity data from literature for the test organisms of the bioassays. Using the MCA method, for each site a numerical value was derived for total environmental risk in the present situation, based on observed effects. In this way, a relative risk ranking of all sites was realized. The MCA values for the present situation were also compared with MCA scores based on estimated risks after remediation in 1995, in order to set priorities for sites where remediation is expected to cause a significant reduction in environmental risk. In most of the 46 sites studied so far, the macrofauna community was poorly developed, judged by a low number of benthic species, low abundances and a high dominance of species regarded as relatively tolerant to chemical pollution. In bioassays high sediment toxicity was demonstrated for 24 sites. Using the sediment quality triad approach, 25 sites were identified as areas where pollution can be held responsible for the effects observed in the field. From a comparison of contaminant concentrations in different types of food with maximum tolerable risk levels, and the application of a bioaccumulation model it was concluded that the sediment pollution also implies high risks for plant-, benthos- or fish-eating birds (secondary poisoning of top predators). In the Nieuwe Merwede highest MCA risk scores were found for shallow parts where highly polluted sediments are found. It is concluded that the sediment quality triad and the MCA provide additional information which can be used to establish priorities for remedial action. Based on an ecotoxicological evaluation of the improved quality of new sediments that will be deposited after removal of the polluted sediments in the Nieuwe Merwede, it is concluded that in this upstream part of the Rhine delta remedial action will be effective. 相似文献
94.
Abstract Multivariate methods for the detection of impacts on communities are: (i) explored in the context of a disturbance experiment at a site of previous uranium mining in Kakadu National Park, Northern Territory; and (ii) applied to the design of a monitoring programme for a proposed mining development at nearby Coronation Hill. The disturbance experiment in Rockhole Mine Creek used a gravity-fed redirection of polluted water from the mine adit to create a point-source pollutant. Weekly samples of the macroinvertebrate communities were taken both before and after disturbance at the control and‘impact’ site, as part of a multivariate BACIP (Before-After-Control-Impact-Pairs) design. The results of the experiment show that the multivariate approach provided high sensitivity in detecting impacts on the community, with little difference in sensitivity between species and family level analyses. A simple procedure for deleting those taxa that show poor discrimination between pristine and presently disturbed areas further increased the sensitivity of the tests. In addition to the BACIP analyses, robust ordination of the community data suggested a time/treatment interaction effect. Application of the multivariate BACIP approach also was explored using baseline data for benthic communities from the South Alligator River near Coronation Hill. The method provides high statistical power for monitoring; a relatively small change in community dissimilarity would be detectable in a programme with 5 years of observations before and after commencement of mining. A robust ordination of the yearly samples for the control and potential-impact sites showed that, although samples varied along identifiable gradients over time, the two areas changed in parallel so that the difference between the areas was approximately constant over years. This result demonstrates that the multivariate BACIP approach can provide relative constancy of pre-impact difference values, a key requirement of BACIP designs that is difficult to satisfy using abundance data for a single species. 相似文献
95.
Antonietta Bernardo Mario Patrizio Giulio Levi Tamara C. Petrucci 《Cellular and molecular neurobiology》1994,14(2):159-173
Summary 1. We have previously shown that acute exposure to the HIV coat protein gp120 interferes with the -adrenergic regulation of astroglial and microglial cells (Leviet al., 1993). In particular, exposure to 100 pM gp120 for 30 min depressed the phosphorylation of vimentin and glial fibrillary acidic protein (GFAP) induced by isoproterenol in rat cortical astrocyte cultures. In the present study we have extended our analysis on the effects of gp120 on astroglial protein phosphorylation.2. We found that chronic (3-day) treatment of the cells with 100 pM gp120 before exposure to isoproterenol was substantially more effective than acute treatment in depressing the stimulatory effect of the -adrenergic agonist on vimentin and GFAP phosphorylation.3. Even after chronic treatment with gp120, no differences were found in the levels and solubility of these proteins.4. Besides stimulating the phosphorylation of intermediate filament proteins, isoproterenol inhibited the incorporation of32P into a soluble acidic protein of 80,000M
r
, which was only minimally present in Triton X-100-insoluble extracts.5. Treatment of astrocytes with a phorbol ester or exposure to3H-myristic acid indicated that the acidic 80,000M
r
protein is a substrate for protein kinase C (PKC) and is myristoylated, thus suggesting that it is related to the MARCKS family of PKC substrates.6. Acute (30-min) treatment with 100 pM gp120 totally prevented the inhibitory effect of isoproterenol on the phorphorylation of the 80,000M
r
MARCKS-like protein.7. Our studies corroborate the hypothesis that viral components may contribute to the neuropathological changes observed in AIDS through the alteration of signal transduction systems in glial cells. 相似文献
96.
Purified thermostable alcohol dehydrogenase allozymes ADH-71k and ADH-FCh.D. ofDrosophila melanogaster have been compared with the two common enzyme forms ADH-F and ADH-S. Enzyme kinetic parameters for various primary and secondary alcohols were determined under standard conditions used previously. Both ADH-71k and ADH-FCh.D. show ADH-S-like reaction kinetics andK
m values, due to retrograde evolution at site 214, Pro Ser. Inhibition studies with alcohol dehydrogenase inhibitors pyrazole, 4-methylpyrazole, and cibacron blue 3GA were also performed. Activity measurements on crude extracts of larvae and flies from isogenic lines of ADH-FCh.D. revealed a consistently higher activity than in ADH-71k-containing strains, in contrast to the original strains.K.Th.E is indebted to the Royal Norwegian Council for Technological and Scientific Research for their postdoctoral fellowship. Prof. J. S. McKinley-McKee gave me the opportunity to work in his laboratory. I thank Dr. Knut Sletten of the Biochemical Institute for the kind gift of 2-methoxyethanol and amino acid analysis of some samples. The Biological Institute, Oslo, Section of General Genetics, is gratefully acknowledged for enabling me to use their fly-breeding facilities. Dr. John B. Gibson provided us with a sample of FCh.D. flies for the construction of isogenic lines in which Dr. Johan Hageman participated, owing to Postdoctoral Grant 436-931-P from the Foundation of Biological Research (BION), which is subsidized by the Netherlands Organization for Scientific Research (NWO). J. H. and Paula Truyens were involved in the measurements on the crude extracts. Work at Victoria University was supported by the VUW Internal Grant Committee. 相似文献
97.
In order to elucidate whether the aphidRhopalosiphum padi is low quality food for the carabid beetleAgonum dorsale, as it has previously been found to be for cereal spiders, we performed a series of experiments using fruit fliesDrosophila melanogaster as a standard alternative prey (‘control prey’): 1) Prey preference, 2) Aphid consumption for satiated and starved beetles,
3) Egg production on different diets and 4) Preference experiments with fruit flies coated with a taste of different prey
types. Other alternative prey types used were earthworms and sciarid midges, all potential prey in the field.A. dorsale has a low preference for aphids compared to fruit flies. Apparently there is an upper limit to the consumption of aphids
independent of hunger and much below the beetles' total food demand. Egg production on a pure diet of aphids is lower than
on a pure diet of fruit flies; it is extremely low on a pure diet of earthworms; the highest fecundity is found on a mixed
diet. As fruit flies coated with a taste of aphids or sciarid midges are less prefered than flies covered with a taste of
fruit flies there may be a chemical factor, acting through taste, involved in determining prey preference. 相似文献
98.
Feeding selectivity by five epilithic, case-building trichopteran species from a first-order stream was examined using laboratory experiments. Larvae had the choice of three food types: periphyton and detritus from the stream, and nettle broth as an artificial food source. Food type influenced the microdistribution of these species. Larvae were able to distinguish between different food types and showed species-specific responses to the various types of food. Drusus annulatus, Micrasema longulum and Apatania fimbriata favoured periphyton, while Agapetus fuscipes and Silo pallipes showed no preference for periphyton over detritus. Four of the five species examined (Apatania fimbriata was the exception) tended to avoid nettle broth. The complexity of foraging behaviour was illustrated by M. longulum. Given a choice between detritus, periphyton and periphyton with the addition of moss, they clearly preferred the latter food type, scraping mostly on the epiphytic algae. Proportions of a given species selecting periphyton were correlated with percentage areas of algae in the gut contents of that species in the field. D. annulatus, M. longulum and A. fimbriata showed the greatest preference for periphyton, and consumed the highest proportions of algae in the field. A. fuscipes and S. pallipes often selected detritus, and these species had the lowest proportions of algae, and the highest proportions of detritus, in their guts. 相似文献
99.
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
100.
Georgina L. Dasilva 《International journal of primatology》1994,15(5):655-680
A group of Colobus polykomosat Tiwai, Sierra Leone, demonstrated seasonal flexibility in its diet, with seeds, young leaves, and mature leaves each dominating
the diet at different times. Comparison of food consumption with phenological data indicates that seeds are eaten whenever
available and are preferred to other foods, while young leaves are preferred to mature leaves. Colobus polykomosalso prefer liane to tree leaves, despite the relatively high quality of mature tree foliage at the Tiwai site. Analysis of
protein, fiber, and energy values of foods selected and items available, but not eaten, suggests that preference is related
to protein and energy maximization. Leguminous plants, especially Papilionaceae and Mimosaceae, are highlighted as important
food sources for C. polykomos;seeds and leaves from these families have a high nitrogen content, and the protein content of leguminous seeds often equals
or exceeds that found in leaves. It is predicted, therefore, that colobines living in habitats with a high density of legumes
will feed heavily on seeds, subject to constraints such as seasonal availability. Where suitable leguminous species are less
common, a mixture of fruits, seeds, and young or mature leaves or both is likely to be selected. The results of this and other
recent studies of colobines do not support the notion that colobines are specialist folivores. 相似文献