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1.
A large bioreactor is heterogeneous with respect to concentration gradients of substrates fed to the reactor such as oxygen and growth limiting carbon source. Gradient formation will highly depend on the fluid dynamics and mass transfer capacity of the reactor, especially in the area in which the substrate is added. In this study, some production-scale (12 m3 bioreactor) conditions of a recombinant Escherichia coli process were imitated on a laboratory scale. From the large-scale cultivations, it was shown that locally high concentration of the limiting substrate fed to the process, in this case glucose, existed at the level of the feedpoint. The large-scale process was scaled down from: (i) mixing time experiments performed in the large-scale bioreactor in order to identify and describe the oscillating environment and (ii) identification of two distinct glucose concentration zones in the reactor. An important parameter obtained from mixing time experiments was the residence time in the feed zone of about 10 seconds. The size of the feed zone was estimated to 10%. Based on these observations the scale-down reactor with two compartments was designed. It was composed of one stirred tank reactor and an aerated plug flow reactor, in which the effect of oscillating glucose concentration on biomass yield and acetate formation was studied. Results from these experiments indicated that the lower biomass yield and higher acetate formation obtained on a large scale compared to homogeneous small-scale cultivations were not directly caused by the cell response to the glucose oscillation. This was concluded since no acetate was accumulated during scale-down experiments. An explanation for the differences in results between the two reactor scales may be a secondary effect of high glucose concentration resulting in an increased glucose metabolism causing an oxygen consumption rate locally exceeding the transfer rate. The results from pulse response experiments and glucose concentration measurements, at different locations in the reactor, showed a great consistency for the two feeding/pulse positions used in the large-scale bioreactor. Furthermore, measured periodicity from mixing data agrees well with expected circulation times for each impeller volume. Conclusions are drawn concerning the design of the scale-down reactor.  相似文献   
2.
First functional events during peroxidation in mitochondria consisted in a progressive inhibition of the phosphorylating and uncoupled respiration with succinate and glutamate/malate as substrates, whereas the resting state respiration during the same period was virtually not influenced. The membrane potential registered at a time with the respiration rates was capable of being built up for a relatively long time interval with only minor decreases, and broke down rather promptly when the active respiration was highly diminished. Inhibition of respiration proceeded mainly during the initiation phase of peroxidation. Lag phases of varied length, of malondialdehyde formation which were predominantly attributed to the iron/protein ratios correlated closely with different time intervals needed to attain maximal inhibition of respiration and decrease in glutathione. Hence, the lessening of respiration, drop of membrane potential and loss of the antioxidant, glutathione, represent early stages in the causal chain of events which precede the onset of intensive lipid peroxidation.  相似文献   
3.
A program DIANA is designed to fit the scanning curves of electrophoresis and ultracentrifugation patterns with 10-15 overlapping peaks by a sum of Gaussian-like distribitions. The parameters of the distributions are adjusted by minimizing x, using a problem oriented minimizing procedure. The number of molecular components as well as starting values of the positions and the widths of the peaks must be choosen as input for each type of pattern. Programs are written in FORTRAN IV.  相似文献   
4.
Summary Eight representative recombinant background clones of λEMBL3 were analysed usingKpnI,BamHI,SalI,EcoRI andHindIII digestion. We found that λEMBL3 carries its own left arm in theBamHI cloning site. In this way, recombinant molecules were found to be generated which can grow onEscherichia coli strain NM539. In all cases analysed, the left arm DNA was inserted in a head to tail orientation. Seven clones carried a restoredBamHI site at thecos site-BamHI site connection. In the region where the inserted left arm and the right arm were ligated,BamHI cloning produces a large palindromic sequence consisting of two polylinkers. ThisBamHI site was incompletely cleaved in all cases analysed. We assume that a part of the λ DNA molecule in this region shows a cruciform structure prohibiting recognition or cleavage of this site by restriction endonucleaseBamHI.  相似文献   
5.
Implantation failure in newly inseminated females induced by exposure to alien males (the Bruce effect) was significantly reduced when the females were housed with the stud male. By contrast, newly inseminated females housed with a familiar male during exposure to alien males exhibited a high rate of implantation failure. The results suggest that the protective effect of the stud male on implantation is not because of the familiarity of the female with his odour cues. The results are consistent with the view that the newly inseminated female mouse identifies her coital partner as an individual because she becomes 'imprinted' with his odour during the pericopulatory period.  相似文献   
6.
We have analysed the effects of oncogenic transformation on the expression of type VI collagen in mesenchymal cells. Synthesis of type VI collagen was almost completely inhibited in fibroblasts transformed by DNA or RNA tumour viruses or in cells derived from spontaneous mesenchymal tumours. Inhibition of type VI collagen synthesis appears, therefore, to be a common phenomenon of transformed mesenchymal cells. When introduced into normal cells by viral vectors, the 'nuclear' oncogene v-myc had an inhibitory effect similar to that of the 'cytoplasmic' oncogene v-src. Fibroblasts infected with a temperature-sensitive strain of Rous sarcoma virus (NY68) produced type VI collagen at the restrictive, but not at the permissive temperature. If such cells were shifted from the permissive to the restrictive temperature, synthesis of the individual subunits of type VI collagen was co-ordinately induced. These results demonstrate that the activity of a single oncogene product is sufficient to inhibit type VI collagen expression.  相似文献   
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8.
Collagen-induced arthritis (CIA) is a rodent arthritis model in which immunization with heterologous type II collagen induces an inflammatory polyarthritis. Susceptibility to the disease is mediated by major histocompatibility complex (MHC) genes as well as genes at other loci. Previous studies of the SWR/J mouse strain, which is resistant to CIA despite bearing the susceptible H-2 q haplotype, have suggested that this resistance is the result of a deletion of T-cell receptor (Tcr) Vb gene segments which is carried by this strain. Other studies have implicated a deficiency in complement component C5 as the cause for the resistance. In order to assess the relative importance of these two genes in susceptibility to CIA, and to provide an estimate of the number of independent genes involved in the disease, we analyzed 196 F2 progeny of a (DBA/1 × SWR/J) cross for arthritis susceptibility, and expression of both C5 and Tcr genes. Thirty of the F2 progeny developed arthritis. All of the arthritic mice had at least one copy of the wild-type C5 allele, while the Tcr-Vb haplotypes were distributed in Mendelian fashion. These results demonstrate that C5 sufficiency is an absolute requirement for CIA, but that Tcr-Vb genes located within the SWR deletion have little influence. Genetic analysis of the incidence rate suggests that there is polygenic control of susceptibility to CIA and that in addition to H-2, 5–6 other independent loci (including C5) may be involved.  相似文献   
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10.
14-d-old conventional piglets were picked from normal piggery, washed with disinfectants, placed into isolators suitable for germfree work, fed a sterile diet and treated with peroral antibiotics (nalidixic acid, kanamycin, and nystatin). Beginning with day 5 or 7, Enterobacteriaceae were not found in feces. The absence of these bacteria was proved by inoculation of germfree newborn piglets with caecal content. In selectively decontaminated piglets, the white blood cell count in blood had fallen to 6 X 10(9)/L; this decrease was due to an extremely low number of granulocytes (to 0.8 X 10(9)/L). On day 35, IgG-positive cells almost disappeared from the spleen, whereas IgA cells were found in an unusually great amount. Corresponding changes in serum levels were established. The colonization resistance effect in Enterobacteriaceae-deprived piglets was confirmed; settling of introduced various E. coli strains did not occur or was delayed.  相似文献   
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