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61.
Spiramycin production by Streptomyces ambofaciens Sp181110 with glucose as the carbon source was studied under a controlled nutritional environment. In a batch culture, the
glucose excess after ammonium depletion led to pyruvate and α-ketoglutarate accumulation. 85 mg/l of spiramycin were produced
in less than 70 h during the stationary and maintenance phase on these acids after glucose exhaustion. Fed-batch strategy
was designed to study spiramycin production without by-product formation and glucose accumulation. In these conditions, up
to 150 mg/l were produced in less than 80 h during the stationary phase on glucose. The antibiotic titre was found independent
of the glucose feeding under carbon limitation and the importance of putative intracellular reserves formed after nutrient
exhaustion was suggested. Besides, spiramycin production was not inhibited by the limiting flux of glucose. 相似文献
62.
José Humberto de Queiroz Jean-Louis Uribelarrea Alain Pareilleux 《Applied microbiology and biotechnology》1993,39(4-5):609-614
The energetics of growth of the fission yeast Schizosaccharomyces pombe was studied in continuous high-cell concentration cultures using a cell-recycle fermentor. Under non-O2-limited conditions, steady-states were obtained at various specific growth rates (partial cell-recycle) with purely oxidative (glucose limitation) or respiro-fermentative (glucose excess) metabolic behaviour. The stoichiometry of biomass synthesis was established from the elemental composition of the cells and measurements of all the specific metabolic rates, i.e. consumption of glucose and O2 and production of CO2, ethanol and other products. The theoretical yield factor for biomass on glucose was YG,X = 0.85 C-mol·C-mol–1 and maintenance requirements were negligible. Assuming a constant coupling between energy generation and biomass formation for both respirative and respiro-fermentative breakdown of glucose, the biomass yield from ATP (YATP) and the efficiency of oxidative phosphorylation (P/O ratio) could be determined as 9.8 g biomass·mol ATP and 1.28 mol ATP·atom of O2, respectively.
Correspondence to: A. Pareilleux 相似文献
63.
64.
Estimating the rate of evolution of the rate of molecular evolution 总被引:35,自引:13,他引:22
A simple model for the evolution of the rate of molecular evolution is
presented. With a Bayesian approach, this model can serve as the basis for
estimating dates of important evolutionary events even in the absence of
the assumption of constant rates among evolutionary lineages. The method
can be used in conjunction with any of the widely used models for
nucleotide substitution or amino acid replacement. It is illustrated by
analyzing a data set of rbcL protein sequences.
相似文献
65.
A simple, fast and sensitive method was developed to verify the presence of
the sialyl Lewis(x) antigen on an N-linked glycoprotein. High performance
liquid chromatography-electrospray mass spectrometry (HPLC-ESI/MS) was used
to identify which of the five N-linked glycosylation sites of human plasma
alpha1-acid-glycoprotein (orosomucoid, OMD) contain the sialyl Lewis(x)
antigen. OMD was digested with proteolytic enzymes and analyzed by reversed
phase chromatography coupled with on-line ESI/MS. A tandem mass
spectrometry experiment was designed to detect the presence of the sialyl
Lewis(x) antigen based on the observation of an 803 mass to charge ratio (
m/z ) ion produced in the intermediate pressure region of the ESI
interface. The ESI/MS signal at m/z 803 is consistent with an oxonium ion
for a glycan structure containing NeuAc, Gal, GlcNAc, and Fuc. The identity
of the m/z 803 ion was confirmed by ESI/MS/MS analysis of the m/z 803
fragment ion and comparison with a sialyl Lewis(x) standard. The
stereochemistry and linkage positions were assigned using previous NMR
analysis but could be determined with permethylation analysis if necessary.
The analysis of OMD gave a pattern showing signal for the sialyl Lewis(x)
antigen coeluting with each of the five N-linked glycopeptides. The ability
to monitor sialyl Lewis(x) expression at each of the five sites is of
interest in the study of OMD's role in inflammatory diseases.
相似文献
66.
67.
Multiple forms of tubulin in the cytoskeletal and flagellar microtubules of polytomella 总被引:14,自引:9,他引:5
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The alga polytomella contains several organelles composed of microtubules, including four flagella and hundreds of cytoskeletal microtubules. Brown and co-workers have shown (1976. J. Cell Biol. 69:6-125; 1978, Exp. Cell Res. 117: 313-324) that the flagella could be removed and the cytoskeletans dissociated, and that both structures could partially regenerate in the absence of protein synthesis. Because of this, and because both the flagella and the cytoskeletons can be isolated intact, this organism is particularly suitable for studying tubulin heterogeneity and the incorporation of specific tubulins into different microtubule-containing organelles in the same cell. In order to define the different species of tubulin in polytonella cytoplasm, a (35)S- labeled cytoplasmic fraction was subjected to two cycles of assembly and disassembly in the presence of unlabeled brain tubulin. Comparison of the labeled polytomella cytoplasmic tubulin obtained by this procedure with the tubulin of isolated polytomella flagella by two-dimensional gel electrophoresis showed that, whereas the β-tubulin from both cytoplasmic and flagellar tubulin samples comigrated, the two α-tubulins had distinctly different isoelectic points. As a second method of isolating tubulin from the cytoplasm, cells were gently lysed with detergent and intact cytoskeletons obtained. When these cytoskeletons were exposed to cold temperature, the proteins that were released were found to be highly enriched in tubulin; this tubulin, by itself, could be assembled into microtubules in vitro. The predominant α-tubulin of this in vitro- assembled cytoskeletal tubulin corresponded to the major cytoplasmic α-tubulin obtained by coassembly of labeled polytomella cytoplasmic extract with brain tubulin and was quite distinct from the α-tubulin of purified flagella. These results clearly show that two different microtubule-containing organelles from the same cell are composed of distinct tubulins. 相似文献
68.
Effect of oxygen tension on human peripheral blood leukocytes: lysosomal enzyme release and metabolic responses during phagocytosis 总被引:2,自引:0,他引:2
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JL Skosey DC Chow S Nusinow J May V Gestautas Y Niwa 《The Journal of cell biology》1981,88(2):358-363
We found that nonlethal lysosomal enzyme release from human peripheral blood leukocytes during phagocytosis of opsonized zymosan in vitro was modified by the oxygen tension under which the cells were incubated; with decreasing Po(2), zymosan-induced release of lysosomal enzymes was potentiated. The effect on enzyme release could not be attributed secondarily to an effect on phagocytosis, because, as others have reported, Po(2) had little effect on that response. Metabolic responses that accompany phagocytosis were also modified by oxygen tension. Stimulation of oxidation by way of the pentose cycle was further enhanced by increasing Po(2). Conversely, anaerobic glycolysis was promoted by decreasing oxygen tension. ATP levels fell as a function of time and concentration of phagocytic stimulus, mirroring lysosomal enzyme release as modified by Po(2). Cyclic AMP levels fell during phagocytosis and lysosomal enzyme release, a change that could act to facilitate lysosomal enzyme release. However, the fall in nucleotide level was greatest with highest Po(2) (i.e., when lysosomal enzyme release was least). The inverse relationship between oxidative metabolism and enzyme release suggested that a product of oxidative metabolism might adversely influence enzyme release. Sulfhydryl antioxidants (Cysteine, glutathione) and scavengers of oxygen-derived reactants (superoxide dismutase, catalase, benzoate, hypoxanthine, xanthine, histidine, azide) all potentiated zymosan- stimulated enzyme release. These findings are consistent with the interpretation that one or more factors (e.g., superoxide anion, hydrogen peroxide, hydroxyl radical, singlet oxygen), generated in association with the burst of oxidative metabolism which accompanies phagocytosis, acts to inhibit lysosomal enzyme release. 相似文献
69.
70.