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1.
AAA ATPases form a functionally diverse superfamily of proteins. Most members form homo-hexameric ring complexes, are catalytically active only in the fully assembled state, and show co-operativity among the six subunits. The mutual dependence among the subunits is clearly evidenced by the fact that incorporation of mutated, inactive subunits can decrease the activity of the remaining wild type subunits. For the first time, we develop here models to describe this form of allostery, evaluate them in a simulation study, and test them on experimental data. We show that it is important to consider the assembly reactions in the kinetic model, and to define a formal inhibition scheme. We simulate three inhibition scenarios explicitly, and demonstrate that they result in differing outcomes. Finally, we deduce fitting formulas, and test them on real and simulated data. A non-competitive inhibition formula fitted experimental and simulated data best. To our knowledge, our study is the first one that derives and tests formal allosteric schemes to explain the inhibitory effects of mutant subunits on oligomeric enzymes. 相似文献
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3.
Bioaccessibility measurements have the potential to improve the accuracy of risk assessments and reduce the potential costs of remediation when they reveal that the solubility of chemicals in a matrix (e.g., soil) differs markedly from that in the critical toxicity study (i.e., the key study from which a toxicological or toxicity reference value is derived). We aimed to apply this approach to a brownfield site contaminated with chromium, and found that the speciation was CrIII, using a combination of alkaline digestion/diphenylcarbazide complexation and X-ray absorption near edge structure analysis. The bioaccessibility of Cr2O3, the compound on which a reference dose for CrIII is based, was substantially lower (<0.1%) than that of the CrIII in the soils, which was a maximum of 9%, giving relative bioaccessibility values of 13,000% in soil. This shows that the reference dose is based on essentially an insoluble compound, and thus we suggest that other compounds be considered for toxicity testing and derivation of reference dose. Two possibilities are CrCl3·6H2O and KCr(SO4)2·12H2O, which have been used for derivation of ecological toxicity reference values and are soluble at a range of dosing levels in our bioaccessibility tests. 相似文献
4.
Summary Aerobic spore-forming bacteria were isolated from plant tissue cultures from a commercial plant cultivation station. Bacillus circulans was found to be a detrimental infectant as a serious consequence of the heat-resistance of the endospores of these bacteria. They were extremely motile, utilized several growth-promoting factors, and could be eliminated by early microscopical identification, killing by heat treatment, or by using antibiotics or disinfecants.Dedicated to Professor Dr. Gustav Kortüm on the occasion of his 80th birthday 相似文献
5.
Summary The distribution and characterization of the opioid octapeptide met5-enkephalin-arg6-gly7-leu8 (met5-enk-arg6-gly7-leu8) within the gastrointestinal tract of the rat has been determined by immunohistochemistry and radioimmunoassay by use of a newly developed antibody to met5-enk-arg6-gly7-leu8. With both techniques, met5-enk-arg6-gly7-leu8-immunoreactivity (met5-enk-arg6-gly7-leu8IR) was detected in all regions of the gastrointestinal (GI) tract except the esophagus. The highest concentration of immunoreactive met5-enk-arg6-gly7-leu8 was observed in the colon, while intermediate concentrations were found in the stomach, duodenum, jejunum, and ileum. Immunostained somata were observed chiefly in the myenteric plexus; immunostained processes were present primarily in the myenteric plexus and the circular muscle layer. This distribution pattern is similar to that previously observed with antiserum to met5-enkephalin-arg6-phe7 (met5-enk-arg6phe7). Chromatographic analysis of met5-enk-arg6-gly7leu8-immunoreactive peptides extracted from the GI tract revealed the presence of an immunoreactive peptide of high molecular weight which accounted for approximately three-quarters of met5-enk-arg6-gly7-leu8-IR in both stomach and colon. These findings suggest a role for peptides related to the octapeptide met5-enk-arg6-gly7-leu8 in the regulation of GI function. 相似文献
6.
7.
The Subcellular Origin of Bioluminescence in Noctiluca miliaris 总被引:4,自引:2,他引:2
The light emitted by Noctiluca has its origin in 1 to 5 x 104 organelles ("microsources") which are scattered throughout the perivacuolar cytoplasm, and which appear to be the elementary functional units of bioluminescence. Microscopical techniques, image intensification, and microphotometry were employed in their investigation. Microsources are fluorescent, strongly phase-retarding, and range widely in diameter below 1.5 microns. The number of quanta emitted in a flash from a microsource ("microflash") is of the order of 105 photons. However, microflashes show a wide range of intensities, which are correlated with the size of the organelles from which they arise. Each organelle responds repetitively and with reproducible time course to a succession of invading triggering potentials. Reversible changes in the intensity of the flash emitted by the whole cell ("macroflash") occur because of graduations in intensity of microflashes rather than as a result of changes in the number of responsive organelles. The shape of the flash emitted by individual microsources resembles that of the macroflash except for slightly shorter rise and decay times. It is concluded that the macroflash results from somewhat asynchronous, but otherwise parallel summation of microflashes. 相似文献
8.
Topology of the transposon Tn10-encoded tetracycline resistance protein within the inner membrane of Escherichia coli 总被引:15,自引:0,他引:15
The transposon Tn10-encoded tetracycline resistance protein TetA is an integral membrane protein responsible for the export of tetracycline from the cytoplasmic to the periplasmic side of the inner membrane of Gram-negative bacteria. From a plot of the average hydrophobicity along the sequence of this protein, a two-dimensional membrane topology with 12 transmembrane domains may be predicted. Using plasmid-bearing Escherichia coli maxicells we specifically radiolabeled the TetA protein. The amino terminus of this membrane protein was shown not to be processed, and its location on the inner side of the cytoplasmic membrane was demonstrated by a newly developed use of a chemical method. Spheroplasts and inside-out vesicles of the TetA protein synthesizing maxicells were subjected to limited digestion by proteases of different specificities. The TetA protein was not accessible to proteases from the periplasmic side. On the inner side of the cytoplasmic membrane, the carboxyl terminus and four sites accessible to endoproteases could be identified. The cleavage sites are proposed to be localized between amino acid residues 60-70, 110-130, 180-200, and at amino acid 327. These results allow the definition of a model for the two-dimensional topology of the TetA protein. 相似文献
9.
Iris D. Zellmer 《Hydrobiologia》1996,319(2):87-92
UV-B (290 nm) tolerance of Daphnia pulex, conditioned to four different food levels (Chlorophyta), was tested under standardized conditions with an artificial radiation source. Parameters measured were survival, percentage of egg bearing Daphnia and the number of juveniles produced after irradiation. UV-B tolerance of Daphnia pulex was found to be significantly improved with increasing food concentrations at all three parameters. The impact of the four different food concentrations on the photoreactivation system was tested with simultanous UV-B and white-light irradiation of Daphnia. Survival rate improved significantly with increasing food levels compared to solely UV-B irradiation. Photoreactivation had no effect on the reproductive parameters. 相似文献
10.
An De Bondt Kristel Eggermont Iris Penninckx Inge Goderis Willem F. Broekaert 《Plant cell reports》1996,15(7):549-554
We have previously developed a protocol for efficient gene transfer and regeneration of transgenic calli following cocultivation of apple (cv. Jonagold) explants with Agrobacterium tumefaciens (De Bondt et al. 1994, Plant Cell Reports 13: 587–593). Now we report on the optimization of postcultivation conditions for efficient and reproducible regeneration of transgenic shoots from the apple cultivar Jonagold. Factors which were found to be essential for efficient shoot regeneration were the use of gelrite as a gelling agent and the use of the cytokinin-mimicing thidiazuron in the selective postcultivation medium. Improved transformation efficiencies were obtained by combining the hormones thidiazuron and zeatin and by using leaf explants from in vitro grown shoots not older than 4 weeks after multiplication. Attempts to use phosphinothricin acetyl transferase as a selectable marker were not successful. Using selection on kanamycin under optimal postcultivation conditions, about 2% of the leaf explants developed transgenic shoots or shoot clusters. The presence and expression of the transferred genes was verified by -glucuronidase assays and Southern analysis. The transformation procedure has also been succesfully applied to several other apple cultivars.Abbreviations BAP
benzylaminopurine
- CTAB
hexadecyltrimethylammoniumbromide
- Na2EDTA
ethylenediamine-tetra-acetate ferric-sodium salt
- FeNaEDTA
ethylenediamine-tetra-acetate ferric-sodium salt
- GA3
gibberellic acid 3
- GusA
-glucuronidase
-
gusA
-glucuronidase gene of Escherichia coli
- IAA
indole acetic acid
- IBA
indole butyric acid
- 2iP
N6-2-isopentenyl adenine
- NAA
naphthalene acetic acid
-
nptII
neomycinphosphotransferase II gene
-
bar
phosphinothricin acetyl transferase gene
- PCR
polymerase chain reaction
- PPT
phosphinothricin
- STS
silver thiosulphate
- T-DNA
transferred DNA
- TDZ
thidiazuron
- X-Gluc
5-bromo-4-chloro-3-indolyl -D-glucuronide
- Zea
trans-Zeatin 相似文献