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291.
292.
The strain N of Trimyema compressum, an anaerobic free-living ciliate, was cultivated axenically in a medium containing a buffered salt solution, yeast extract, trypticase, and glutathione. Dead bacteria were indispensable as food; a culture of the ciliate together with heat-killed Klebsiella pneumoniae has been established for more than one year. In the medium described, the ciliates grow to a higher cell density than in cultures with living bacteria as food. During the process of axenization, a nonmethanogenic bacterial endosymbiont was lost. In the microbodies of T. compressum, hydrogenase could be localized by the technique of indirect immunofluorescence. 相似文献
293.
E. J. Middelbeek H. H. A. M. van de Laar J. M. H. Hermans C. Stumm G. D. Vogels 《Antonie van Leeuwenhoek》1980,46(5):483-497
The interaction between the killer toxin of Pichia kluyveri 1002 and cells of Saccharomyces cerevisiae SCF 1717 is strongly affected by the physiological state of sensitive cells. The killing effect is maximal for cells in the lag and early exponential phase of growth, whereas stationary cells are completely resistant. Furthermore, sensitivity is markedly enhanced by a rise of the pH (from 3.2 to 6.8) at which cells are cultured.Three successive stages can be distinguished in the killing process: (I) binding of the toxin to the primary binding site; (II) transmission of the toxin to its reactive site in the plasma membrane; (III) occurrence of functional damage (K+-leakage; decrease of intracellular pH). The transition from stage I to II is prevented in the absence of metabolic energy or at low temperature (below 10°C). Sensitive cells in stage I can be rescued from toxin-induced killing by a short incubation at pH 7.0, which treatment is not effective for cells in stage II. Cells in stage II are able to resume growth when plated in a rich medium containing suitable concentrations of potassium and hydrogen ions. Rescue was not observed for cells in stage III of the killing process. 相似文献
294.
Cytosolic enzymes with a mitochondrial ancestry from the anaerobic chytrid Piromyces sp. E2 总被引:4,自引:2,他引:2
Anna Akhmanova Frank G. J. Voncken Harry Harhangi Ken M. Hosea Godfried D. Vogels & Johannes H. P. Hackstein 《Molecular microbiology》1998,30(5):1017-1027
The anaerobic chytrid Piromyces sp. E2 lacks mitochondria, but contains hydrogen-producing organelles, the hydrogenosomes. We are interested in how the adaptation to anaerobiosis influenced enzyme compartmentalization in this organism. Random sequencing of a cDNA library from Piromyces sp. E2 resulted in the isolation of cDNAs encoding malate dehydrogenase, aconitase and acetohydroxyacid reductoisomerase. Phylogenetic analysis of the deduced amino acid sequences revealed that they are closely related to their mitochondrial homologues from aerobic eukaryotes. However, the deduced sequences lack N-terminal extensions, which function as mitochondrial leader sequences in the corresponding mitochondrial enzymes from aerobic eukaryotes. Subcellular fractionation and enzyme assays confirmed that the corresponding enzymes are located in the cytosol. As anaerobic chytrids evolved from aerobic, mitochondria-bearing ancestors, we suggest that, in the course of the adaptation from an aerobic to an anaerobic lifestyle, mitochondrial enzymes were retargeted to the cytosol with the concomitant loss of their N-terminal leader sequences. 相似文献
295.
296.
297.
Wim J.B. Wannet Huub J.M. Op den Camp Hendrik W. Wisselink Chris van der Drift Leo J.L.D. Van Griensven Godfried D. Vogels 《Biochimica et Biophysica Acta (BBA)/General Subjects》1998,1425(1):177-188
Trehalose phosphorylase (EC 2.4.1.64) from Agaricus bisporus was purified for the first time from a fungus. This enzyme appears to play a key role in trehalose metabolism in A. bisporus since no trehalase or trehalose synthase activities could be detected in this fungus. Trehalose phosphorylase catalyzes the reversible reaction of degradation (phosphorolysis) and synthesis of trehalose. The native enzyme has a molecular weight of 240 kDa and consists of four identical 61-kDa subunits. The isoelectric point of the enzyme was pH 4.8. The optimum temperature for both enzyme reactions was 30°C. The optimum pH ranges for trehalose degradation and synthesis were 6.0–7.5 and 6.0–7.0, respectively. Trehalose degradation was inhibited by ATP and trehalose analogs, whereas the synthetic activity was inhibited by Pi (Ki=2.0 mM). The enzyme was highly specific towards trehalose, Pi, glucose and α-glucose-1-phosphate. The stoichiometry of the reaction between trehalose, Pi, glucose and α-glucose-1-phosphate was 1:1:1:1 (molar ratio). The Km values were 61, 4.7, 24 and 6.3 mM for trehalose, Pi, glucose and α-glucose-1-phosphate, respectively. Under physiological conditions, A. bisporus trehalose phosphorylase probably performs both synthesis and degradation of trehalose. 相似文献
298.
A recent study has shown that neurons in the inferior temporal cortex of the macaque monkey brain show earlier selectivity to global and large shapes than to local and small ones, which may underlie the faster behavioral responses to global aspects of a scene. 相似文献
299.
Servé W. M. Kengen Piet J. H. Daas Jan T. Keltjens Chris van der Drift Godfried D. Vogels 《Archives of microbiology》1990,154(2):156-161
The conversion of formaldehyde to methylcoenzyme M in cell-free extracts of Methanobacterium thermoautotrophicum was stimulated up to 10-fold by catalytic amounts of the heterodisulfide (CoM-S-S-HTP) of coenzyme M and 7-mercaptoheptanoylthreonine phosphate. The stimulation required the additional presence of ATP, also in catalytic concentrations. ATP and CoM-S-S-HTP were mutually stimulatory on the methylcoenzyme M formation and it was concluded that the compounds were both involved in the reductive activation of the methyltetrahydromethanopterin: coenzyme M methyltransferase. Micromolar concentrations of benzyl viologen or cyanocobalamin inhibited the formaldehyde conversion; these compounds, however, strongly stimulated the reduction of CoM-S-S-HTP. The results described here closely resemble observations made on the activation and reduction of CO2 to formylmethanofuran indicating that this step and the reductive activation of the methyltransferase are controlled by some common mechanism.Abbreviations HS-CoM
Coenzyme M, 2-mercaptoethanesulfonate
- CH3S-CoM
methylcoenzyme M, 2-(methylthio)ethanesulfonate
- H4MPT
5,6,7,8-tetrahydromethanopterin
- MFR
methanofuran
- HS-HTP
7-mercaptoheptanoylthreonine phosphate
- CoM-S-S-HTP
the heterodisulfide of HS-CoM and HS-HTP
- BES
2-bromoethanesulfonate
- TES
N-tris(hydroxymethyl)methyl-2-aminoethanesulfonate
- CN-Cbl
cyanocobalamin
- HO-Cbl
hydroxycobalamin
- HBI
5-hydroxybenzimidazole
- DMBI
5,6-dimethylbenzimidazole 相似文献
300.
Justin W. Hicks Christian B. Kyle Christopher M. Vogels Susan L. Wheaton Felix J. Baerlocher Andreas Decken Stephen A. Westcott 《化学与生物多样性》2008,5(11):2415-2422
Addition of thiosemicarbazide, 4‐allylthiosemicarbazide, and 4‐phenylthiosemicarbazide to (formylphenyl)boronic acids affords a series of thiosemicarbazones containing boronic acids. Addition of 2‐formylphenylboronic acid to the thiosemicarbazides gave the corresponding cyclic 2,3,1‐benzodiazaborines. All new compounds have been investigated for potential antifungal activity. 相似文献