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1.
Continuous fermentations were carried out involving competition between two strains of Saccharomyces cerevisiae. One of the strains has a lower specific growth rate and is very flocculent, whereas the fastergrowing strain is nonflocculent. The product stream from the chemostat was fed into an inclined settler where the flocculent strain was partially separated from the nonflocculent strain as a result of the higher sedimentation rate of the flocculent cells. The underflow from the inclined settler, which was concentrated and enriched with flocculent cells, was recycled to the chemostat. When no recycle was used, the fastergrowing, nonflocculent yeast rapidly overtook the culture. With selective recycle, however, the experiments demonstrated that the slower-growing flocculent yeast could be maintained as the dominant species. A theoretical development is also presented in order to describe the competition between two strains in the bioreactor-settler system. The concept of selective recycle via selective flocculation and sedimentation offers a possible means of maintaining unstable recombinant microorganisms in continuous fermentations. 相似文献
2.
Hormonal imprinting takes place at the first encounter of the hormone and receptor, and results in a changed binding capacity and reaction of the cell and its progeny generations. The imprinting effect of three amino acids and their oligopeptides is studied using fluorescent-labelled peptides. Glycine and lysine could provoke positive imprinting (increased binding in the progeny generations) for their own peptides, but alanine could not. Mostly positive imprinting was provoked by glycine and lysine peptides for their own peptides of different chain length. The optimal chain length provoking self-imprinting was four for glycine, two for lysine and three for alanine. Except in this case, alanine was neutral or provoked mostly negative imprinting. After reaching the optimal chain length, there is a decline in binding. Evolutionary conclusions are discussed. 相似文献
3.
Protein recovery from a bacterial lysate was accomplished using microfiltration membranes in a flat crossflow filter and in a cylindrical rotary filter. Severe membrane fouling yielded relatively low long-term permeate flux values of 10(-4)-10(-3) cm/s (where I cm/s = 3.6 x 10(4) L/m(2) - h). The permeate flux was found to be nearly independent of transmembrane pressure and to increase with increasing shear rate and decreasing solids concentration. The flux increased with shear to approximately the one-third power or greater for the flat filter and the one-half power or greater for the rotary filter; the stronger dependence for the rotary filter is thought to result from Taylor vortices enhancing the back transport of debris carried to the membrane surface by the permeate flow. The average protein transmission or sieving coefficient was measured at approximately 0.6, but considerable scatter in the transmission data was observed. The largest sieving coefficients were obtained for dilute suspensions at high shear rate. The rotary filter provided higher fluxes than did the flat filter for dilute suspensions, but not for concentrated suspensions. (c) 1995 John Wiley & Sons, Inc. 相似文献
4.
In the carrageenin-induced granuloma of rats the inflammatory tissue growth and macrophage invasion on the one hand and the cyclic-AMP content of the macrophages on the other, display opposite directional changes. Macrophages, isolated from this tissue at different stages of inflammation, were used to examine the effect of prostaglandin E2 on intracellular levels of c-AMP. It appears that during infiltration of the macrophages into the inflammatory tissue, the sensitivity of adenylate cyclase to activation by PGE2 increases. Arguments are presented that these observations made
, are in direct relevance to the previously described anti-inflammatory effect of PGE on granuloma tissue
. 相似文献
5.
Comparison of the effects of inhibitors of cytochrome P-450-mediated reactions on human platelet aggregation and arachidonic acid metabolism 总被引:2,自引:0,他引:2
Metyrapone and SKF-525A, together with amphenone B, a structural analogue of metyrapone, which are all inhibitors of cytochrome P-450-mediated reactions, were shown to inhibit the arachidonic acid-induced aggregation of human platelets. Amphenone B, like metyrapone, exhibited a type II (ligand) binding spectrum with rat liver microsomal cytochrome P-450, in contrast to SKF 525A which is a type I (substrate) binding agent. Independently of their type of binding spectra and of their maximum spectral change, however, the affinity of the three compounds for rat liver cytochrome P-450 showed a close proportional correlation with their platelet aggregation inhibitory potency. All three compounds inhibited the formation of [1-14C]thromboxane B2 from [1-14C]arachidonic acid by human platelets aggregated with collagen. The effect of metyrapone on the remaining labelled products suggested that it is a selective thromboxane synthesis inhibitor, while amphenone B exhibited activity reminiscent of cyclo-oxygenase inhibitors. SKF 525A produced complex effects possibly attributable to cyclo-oxygenase inhibition and enhanced lipid peroxidation, since it also enhanced platelet malonaldehyde formation, which the other two compounds inhibited. These data provide further support for a role of cytochrome P-450 in thromboxane synthesis and platelet aggregation. 相似文献
6.
When an γ‐irradiated Dy‐, Tm‐, Sm‐ or Mn‐doped CaSO4 crystal is impulsively deformed, two peaks appear in the ML intensity versus time curve, whereby the first ML peak is found in the deformation region and the second in the post‐deformation region of the crystals. In this study, intensities Im1 and Im2 corresponding to first and second ML peaks, respectively, increased linearly with an impact velocity v0 of the piston used to deform the crystals, and times tm1 and tm2 corresponding to the first and second ML peaks, respectively, decreased with impact velocity. Total ML intensity initially increased with impact velocity and then reached a saturation value for higher values of impact velocity. ML intensity increased with increasing γ‐doses and size of crystals. Results showed that the electric field produced as a result of charging of newly‐created surfaces caused tunneling of electrons to the valence band of the hole‐trapping centres. The free holes generated moved in the valence band and their subsequent recombination with electron trapping centres released energy, thereby resulting in excitation of luminescent centres. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
7.
Bin Jiang Jeffrey Mason Anahid Jewett Jun Qian Yijiang Ding William CS Cho Xichen Zhang Yan-gao Man 《International journal of biological sciences》2013,9(1):119-133
Background: Colorectal carcinogenesis is believed to be a multi-stage process that originates with a localized adenoma, which linearly progresses to an intra-mucosal carcinoma, to an invasive lesion, and finally to metastatic cancer. This progression model is supported by tissue culture and animal model studies, but it is difficult to reconcile with several well-established observations, principally among these are that up to 25% of early stage (Stage I/II), node-negative colorectal cancer (CRC) develop distant metastasis, and that circulating CRC cells are undetectable in peripheral blood samples of up to 50% of patients with confirmed metastasis, but more than 30% of patients with no detectable metastasis exhibit such cells. The mechanism responsible for this diverse behavior is unknown, and there are no effective means to identify patients with pending, or who are at high risk for, developing metastatic CRC.Novel findings: Our previous studies of human breast and prostate cancer have shown that cancer invasion arises from the convergence of a tissue injury, the innate immune response to that injury, and the presence of tumor stem cells within tumor capsules at the site of the injury. Focal degeneration of a capsule due to age or disease attracts lymphocyte infiltration that degrades the degenerating capsules resulting in the formation of a focal disruption in the capsule, which selectively favors proliferating or “budding” of the underlying tumor stem cells. Our recent studies suggest that lymphocyte infiltration also triggers metastasis by disrupting the intercellular junctions and surface adhesion molecules within the proliferating cell buds causing their dissociation. Then, lymphocytes and tumor cells are conjoined through membrane fusion to form tumor-lymphocyte chimeras (TLCs) that allows the tumor stem cell to avail itself of the lymphocyte''s natural ability to migrate and breach cell barriers in order to intravasate and to travel to distant organs. Our most recent studies of human CRC have detected nearly identical focal capsule disruptions, lymphocyte infiltration, budding cells, and the formation of TLCs. Our studies have further shown that age- and type-matched node-positive and -negative CRC have a significantly different morphological and immunohistochemical profile and that the majority of lymphatic ducts with disseminated cells are located within the mucosa adjacent to morphologically normal appearing epithelial structures that express a stem cell-related marker.New hypothesis: Based on these findings and the growth patterns of budding cells revealed by double immunohistochemistry, we further hypothesize that metastatic spread is an early event of carcinogenesis and that budding cells overlying focal capsule disruptions represent invasion- and metastasis-initiating cells that follow one of four pathways to progress: (1) to undergo extensive in situ proliferation leading to the formation of tumor nests that subsequently invade the submucosa, (2) to migrate with associated lymphocytes functioning as “seeds” to grow in new sites, (3) to migrate and intravasate into pre-existing vascular structures by forming TLCs, or (4) to intravasate into vascular structures that are generated by the budding cells themselves. We also propose that only node-positive cases harbor stem cells with the potential for multi-lineage differentiation and unique surface markers that permit intravasation. 相似文献
8.
9.
The correlation of protein structure and evolution of a protein-coding gene: phylogenetic inference using cytochrome oxidase III 总被引:1,自引:1,他引:0
Discriminating phylogenetic signal from noise in DNA sequence data is a
difficult problem in phylogenetic inference at higher systematic levels.
For protein-coding genes, noise at synonymous (silent) positions can be
filtered by deleting entire codon positions or types of change at a codon
position. This method is not appropriate for replacement sites, because
changes at each site within a codon may not be independent. This research
presents a method using information from protein structure to evaluate
variation in replacement sites. Analysis of the correlation of amino acid
variation with protein structure identified rapidly evolving codons in the
COIII gene. In a series of phylogenetic analyses attempting to recover a
known set of vertebrate relationships, downweighting these labile codons
produced the most accurate results. Structural correlates of variable and
invariant residues identified in this study can be used to increase the
accuracy of models used for phylogenetic inference. Viewing amino acid
variation within a phylogenetic framework provided insight into residue
changes important in the secondary and tertiary structures of the molecule,
changes that were correlated between pairs of neighboring residues or
between residues in neighboring helices.
相似文献
10.
Andréia S Lessa Bruno D Paredes Juliana V Dias Adriana B Carvalho Luiz Fernando Quintanilha Christina M Takiya Bernardo R Tura Guilherme FM Rezende Antonio C Campos de Carvalho Célia MC Resende Regina CS Goldenberg 《BMC veterinary research》2010,6(1):1-10