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1.
Oxygen inhibition of nitrate uptake is a general regulatory mechanism in nitrate respiration 总被引:8,自引:0,他引:8
It has recently been demonstrated that oxygen inhibits nitrate uptake by denitrifying Pseudomonas aeruginosa. The purpose of the present investigation was to determine if this novel mechanism of regulation is universal for the regulation of nitrate respiration in other widely divergent species of bacteria. Nitrate transport by whole cell suspensions was completely and reversibly inhibited in 11 out of 12 species tested, whereas nitrate reduction by cell-free extracts was not affected by oxygen or was only partially inhibited in some cases. These results indicate that oxygen inhibition of nitrate uptake is a general regulatory phenomenon. 相似文献
2.
3.
Michael H Woo John R Vance Ana R Otero Marcos Christian Bailly Mary-Ann Bjornsti 《The Journal of biological chemistry》2002,277(6):3813-3822
DNA topoisomerase I (Top1p) catalyzes topological changes in DNA and is the cellular target of the antitumor agent camptothecin (CPT). Non-CPT drugs that target Top1p, such as indolocarbazoles, are under clinical development. However, whether the cytotoxicity of indolocarbazoles derives from Top1p poisoning remains unclear. To further investigate indolocarbazole mechanism, rebeccamycin R-3 activity was examined in vitro and in yeast. Using a series of Top1p mutants, where substitution of residues around the active site tyrosine has well-defined effects on enzyme catalysis, we show that catalytically active, CPT-resistant enzymes remain sensitive to R-3. This indolocarbazole did not inhibit yeast Top1p activity, yet was effective in stabilizing Top1p-DNA complexes. Similar results were obtained with human Top1p, when Ser or His were substituted for Asn-722. The mutations altered enzyme function and sensitivity to CPT, yet R-3 poisoning of Top1p was unaffected. Moreover, top1delta, rad52delta yeast cells expressing human Top1p, but not catalytically inactive Top1Y723Fp, were sensitive to R-3. These data support hTop1p as the cellular target of R-3 and indicate that distinct drug-enzyme interactions at the active site are required for efficient poisoning by R-3 or CPT. Furthermore, resistance to one poison may potentiate cell sensitivity to structurally distinct compounds that also target Top1p. 相似文献
4.
Summary The effects of varying the pH of the cocultivation medium, additons of vir-inducing phenolic compounds and the strains of wild-type agrobacteria on transformation rates of a number of different varieties of Antirrhinum majus were studied. In general, optimal transformation was found with strains C58 or A281 and was favoured by low pH and the inclusion of acetosyringone in the co-cultivation medium. However, maximal transformation of the least susceptible variety was achieved at high pH and in the presence of syringaldehyde. This demonstrates the need for the optimization of a wide range of culture conditions when working with new genotypes and offers a rational approach towards the development of Agrobacterium-mediated transformation of new species or varieties.Abbreviations BAP
6-benzylaminopurine
- MS
Murashige and Skoog medium (Murashige and Skoog, 1962)
- NOA
naphthoxyacetic acid 相似文献
5.
A Shafiee M Vosooghi C G Francisco R Freire R Hernandez J A Salazar E Suarez S Sotheeswaran A A Gunatilaka 《Steroids》1987,49(4-5):397-402
The chemical synthesis and physical data of several new esters of testosterone (17 beta-hydroxyandrost-4-en-3-one), which contain either a halogeno or an alkoxy substituent in the acid chain, are reported. 相似文献
6.
7.
Phencyclidine (PCP; 20 micrograms in 0.5 microliter) was tested by local brain injection for neurochemical effects in the nucleus accumbens and striatum of rats. Changes in dopamine turnover could not be detected in postmortem tissue assays. In contrast, extracellular levels of dopamine significantly increased as measured by microdialysis in freely moving animals. PCP also increased extracellular levels of serotonin and decreased 3,4-dihydroxyphenylacetic acid (DOPAC), but did not change homovanillic acid (HVA) or 5-hydroxyindoleacetic acid (5HIAA). Microdialysis suggests that PCP acts in some dopamine terminal regions to increase extracellular dopamine and serotonin. 相似文献
8.
The present study was carried out to evaluate the suitability of the unstable white-zeste system in Drosophila melanogaster by testing 4 organophosphorus insecticides for potential genotoxic activity: dimethoate, fenitrothion, malathion, and methyl parathion. In view of the high sensitivity to insecticides of the unstable zeste strain used in this assay and the negative results obtained in this work, the white-zeste system does not appear to be sufficiently accurate for the evaluation of the mutagenic potential of specifically toxic chemicals, like insecticides. 相似文献
9.
M Hernandez Bronchud S Webb M M Esiri 《The journal of histochemistry and cytochemistry》1988,36(9):1191-1195
We developed a method to detect multiple DNA copies (both cellular and viral) in specific brain regions by blotting thick frozen sections onto nylon membranes. This was achieved by "printing" the frozen sections on standard blotting paper immediately after cryotome sectioning and performing blotting according to the standard Southern technique. A "replica" of the blotted section was obtained by keeping on the glass slide the next frozen section cut, which was then stained for conventional histopathological analysis and the cell nuclei counted to give an estimate of the total amount of DNA present in each section. The blotted membranes were then denatured and hybridized with a nick-translated Alu probe either at 42 degrees C with 50% formamide or at 68 degrees C without formamide. Brain sections from mice infected with Herpes simplex virus 1 (HSV1), blotted and hybridized with a nick-translated HSV1 probe, clearly showed the focal nature of the Herpes simplex infection, which was also demonstrated immunohistologically using a virus specific antiserum. This method of DNA detection, conveniently modified, might also be used to detect nuclear and cytoplasmic RNAs in specific coronal sections of whole brain before localization at high power by standard in situ techniques. 相似文献
10.
Charles R. Ill Tammy Brehm Bjorn K. Lydersen Rachel Hernandez Karen G. Burnett 《In vitro cellular & developmental biology. Plant》1988,24(5):413-419
Summary Studies with Human x Human (HxH), Human x Mouse (HxM), and Mouse x Mouse (MxM) hybridomas have enabled us to define specific
factors that affect hybridoma growth in a species-specific manner. Three transferrins and three lipophilic iron chelates have
been tested for their ability to support hybridoma proliferation and antibody production. The results of these studies demonstrate
that HxH hybridomas do not respond to bovine transferrin a+ concentrations up to 100 μg/ml and are approximately 100-fold less responsive to mouse transferrin than to human transferrin.
HxM and MxM hybridomas respond equally to human or mouse transferrin but are 100-fold less sensitive to bovine transferrin.
An antibody to the human transferrin receptor inhibited the growth-promoting activity of human or mouse transferrin on HxH
hybridomas but was ineffective on HxM hybridomas. This semonstrated the functionality of the human transferrin receptor in
HxH hybridomas and that human, mouse, and bovine transferrin were interacting through the mouse transferrin receptor in HxM
hybridomas. HxH and HxM hybridomas respond similarly to three different iron chelates exhibiting 80 to 110% of the growth
response to human transferrin. MxM hybridomas fail to respond to the iron chelates at similar concentrations, suggesting that
the human genome present in the other hybridoma species confers a unique ability for utilizing iron when delivered in this
form. 相似文献