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1.
Ion-exchange chromatography of extracts derived from Chlorella sorokiniana mutant strain (oxygen resistant) yielded two separate activity peaks of glutamine synthetase (GS). GSI and GSII were purified 220- and 187-fold and have molecular weights of approximately 398,000 and 360,000, respectively. Both enzymes are composed of eight identical subunits with a subunit molecular weight of 47,000 for GSI and 43,000 for GSII. The amino acid composition, catalytic, and immunological properties for both enzymes are similar. 相似文献
2.
Nitrogen-limited cells of the obligate chemolithotroph Thiobacillus neapolitanus formed an intracellular polymer during growth in the chemostat. This polymer was isolated and characterized as a branched polyglucose composed of units joined by -14 and -16 linkages. Polyglucose in T. neapolitanus can be considered a storage compound since formation of this compound took place during excess of energy and CO2 whilst shortage of CO2 resulted in rapid breakdown of polyglucose. Moreover the breakdown of polyglucose generated metabolically useful energy as could be demonstrated by polyglucose-dependent protein synthesis. Possession of polyglucose did not influence the viability of T. neapolitanus during prolonged periods of energy starvation. Activities of key enzymes of the oxidative pentose phosphate cycle, glucose-6-phosphatedehydrogenase and 6-phospho-gluconate-dehydrogenase, were demonstrated in cell free extracts of T. neapolitanus and appeared to increase 5- and 3-fold, respectively, during growth on NO
3
-
instead of NH
4
+
as a nitrogen source. 相似文献
3.
Reactivity versus flexibility in thiobacilli 总被引:3,自引:0,他引:3
The results of ecophysiological studies on obligately and facultatively chemolithotrophic thiobacilli performed over the past years clearly show that the two types of organisms occupy different ecological niches. Chemostat experiments with cultures of the obligate chemolithotroph Thiobacillus neapolitanus and the facultative chemolithotroph Thiobacillus A2 have been carried out to explain the competitiveness of T. neapolitanus under conditions of strongly fluctuating substrate supply.
Thiobacillus neapolitanus appeared to be very resistant to starvation periods whereafter it could oxidize sulfide (or thiosulfate) almost instantaneously at the original rate. Under alternate supply of 4 h sulfide and 4 h sulfate (or acetate which does not support growth of the organism either) to a chemostat culture of T. neapolitanus (D=0.05 h–1) the sulfide concentration in the growth vessel never reached levels higher than 4m. This strategy is aimed at maximal reactivity. In contrast to T. neapolitanus the facultative chemolithotroph T.A2 appeared to be very flexible with respect to its energy generation. Under alternate supply of 4 h sulfide and 4 h acetate (D=0.05 h–1) T.A2 was able to grow continuously since it directed its metabolism to either heterotrophy or autotrophy by rapid induction-repression mechanisms. This flexible strategy seems to be incompatible with a reactive strategy within one organism, since the oxidation capacity for sulfide decreased during the acetate period resulting in accumulation of sulfide during the sulfide period. It is concluded that T.A2 needs a continuous supply of an inorganic and an organic substrate to thrive whereas T. neapolitanus needs only a continuous supply of a reduced inorganic sulfur source but also will persist in environments with interrupted addition of sulfide provided that the starvation period does not last too long. 相似文献
4.
5.
Histopathological effects of cisplatin,doxorubicin and 5-flurouracil (5-FU) on the liver of male albino rats
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Hassan I El-Sayyad Mohamed F Ismail F M Shalaby RF Abou-El-Magd Rajiv L Gaur Augusta Fernando Madhwa HG Raj Allal Ouhtit 《International journal of biological sciences》2009,5(5):466-473
Cisplatin, doxorubicin and fluorouracil (5-FU), drugs belonging to different chemical classes, have been extensively used for chemotherapy of various cancers. Despite extensive investigations into their hepatotoxicity, there is very limited information on their effects on the structure and ultra-structure of liver cells in vivo. Here, we demonstrate for the first time, the effects of these three anticancer drugs on rat liver toxicity using both light and electron microscopy. Light microscopic observations revealed that higher doses of cisplatin and doxorubicin caused massive hepatotoxicity compared to 5-FU treatment, including dissolution of hepatic cords, focal inflammation and necrotic tissues. Interestingly, low doses also exhibited abnormal changes, including periportal fibrosis, degeneration of hepatic cords and increased apoptosis. These changes were confirmed at ultrastructural level, including vesiculated rough endoplasmic reticulum and atrophied mitochondria with ill-differentiated cisternae, dense collection of macrophages and lymphocytes as well as fibrocytes with collagenous fibrils manifesting early sign of fibrosis, especially in response to cisplatin and doxorubicin -treatment. Our results provide in vivo evidence, at ultrastructural level, of direct hepatotoxicity caused by cisplatin, doxorubicin and 5-FU at both light and electron microscopi. These results can guide the design of appropriate treatment regimen to reduce the hepatotoxic effects of these anticancer drugs. 相似文献
6.
Joana RF Abreu Daphne de Launay Marjolein E Sanders Aleksander M Grabiec G Marleen van de Sande Paul P Tak Kris A Reedquist 《Arthritis research & therapy》2009,11(4):R121-13
Introduction
Fibroblast-like synoviocytes (FLS) from rheumatoid arthritis (RA) patients share many similarities with transformed cancer cells, including spontaneous production of matrix metalloproteinases (MMPs). Altered or chronic activation of proto-oncogenic Ras family GTPases is thought to contribute to inflammation and joint destruction in RA, and abrogation of Ras family signaling is therapeutic in animal models of RA. Recently, expression and post-translational modification of Ras guanine nucleotide releasing factor 1 (RasGRF1) was found to contribute to spontaneous MMP production in melanoma cancer cells. Here, we examine the potential relationship between RasGRF1 expression and MMP production in RA, reactive arthritis, and inflammatory osteoarthritis synovial tissue and FLS. 相似文献7.
8.
Three wheat samples collected in 1987 in Central Poland and naturally infected withFusarium spp were analyzed for the presence ofFusarium spp andFusarium toxins. Heads were separated into three fractions: kernels with visibleFusarium damage, healthy looking kernels, and chaff + rachis. The samples contained deoxynivalenol (2.0 – 40.0μg/g), nivalenol (O.O1μg/g), 4,7-dideoxynivalenol (0.10 – 0.15μg/g). 15-acetyldeoxynivalenol (0.10–2.00 μg/g), 3-acetyldeoxynivalenol (O/1Oμg/g), and zearalenone (0.01–2.00μg/g). This is the first report about 15 - acetyldeoxynivalenol in European wheat and the co-occurrence of 3 - acetyldeoxynivalenol and 15-acetyldeoxynivalenol in the same sample of contaminated cereals. 相似文献
9.
R. F. Beudeker G. C. Cannon J. G. Kuenen J. M. Shively 《Archives of microbiology》1980,124(2-3):185-189
An adaptation of the d-ribulose-1,5-bisphosphate carboxylase (RuBPCase) activity to changing CO2 concentrations in the growth medium in the chemostat was observed in the obligate chemolithotroph Thiobacillus neapolitanus. RuBPCase activity has been separated in a soluble and particulate fraction. The activity of the particulate fraction appeared to be associated with the carboxysomes.The total activity of RuBPCase of CO2 limited cultures was about 5-fold higher than the activity of thiosulphate limited cultures grown in the presence of 5% CO2 whilst the particulate activity and the soluble activity were about 8- and 1.5-fold higher, respectively. The fluctuation of the total and particulate RuBPCase activity correlated with the changes in volume density of carboxysomes in the cell.An inverse correlation between maximal CO2 fixing capacity by whole cells and the volume density of carboxysomes was observed. The change in ratio of soluble RuBPCase activity to particulate RuBPCase activity paralleled the change in maximal CO2 fixation by whole cells during the different growth conditions. 相似文献
10.
Multiple duplications of yeast hexose transport genes in response to selection in a glucose-limited environment 总被引:11,自引:2,他引:9
When microbes evolve in a continuous, nutrient-limited environment, natural
selection can be predicted to favor genetic changes that give cells greater
access to limiting substrate. We analyzed a population of baker's yeast
that underwent 450 generations of glucose-limited growth. Relative to the
strain used as the inoculum, the predominant cell type at the end of this
experiment sustains growth at significantly lower steady-state glucose
concentrations and demonstrates markedly enhanced cell yield per mole
glucose, significantly enhanced high-affinity glucose transport, and
greater relative fitness in pairwise competition. These changes are
correlated with increased levels of mRNA hybridizing to probe generated
from the hexose transport locus HXT6. Further analysis of the evolved
strain reveals the existence of multiple tandem duplications involving two
highly similar, high- affinity hexose transport loci, HXT6 and HXT7.
Selection appears to have favored changes that result in the formation of
more than three chimeric genes derived from the upstream promoter of the
HXT7 gene and the coding sequence of HXT6. We propose a genetic mechanism
to account for these changes and speculate as to their adaptive
significance in the context of gene duplication as a common response of
microorganisms to nutrient limitation.
相似文献