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Baby hamster kidney (BHK) cell aggregates grown in stirred vessels with different working volumes and impeller sizes were characterized. Using batch cultures, the range of agitation rates studied (25-100 rpm) led to aggregates with maximum sizes of 150 mum. Necrotic centers were not observed and cell specific productivity was independent of aggregate size. High cell viability was found for both single and adherent cells without an increase in cell death when agitation rate was increased. The increase in agitation rate affected aggregates by reducing their size and increasing their concentration and cell concentration in aggregates, while increasing the fraction of free cells in suspension. The experimental relationship between aggregate size and power dissipation rate per unit of mass was close to -1/4, suggesting a correlation with a critical turbulence microscale; this was independent of vessel scale and impeller geometry over the range investigated. Viscous stresses in the viscous dissipation subrange (below Kolmogoroff eddies) appear to be responsible for aggregate breakage. Under intense agitation BHK cells grown in the absence of microcarriers existed as aggregates without cell damage, whereas cells grown on the surface of microcarriers were largely reduced. This is a clear advantage for scaleup purposes if aggregates are used as a natural immobilization system in stirred vessels. (c) 1995 John Wiley & Sons, Inc. 相似文献
54.
Current phylogenetic tree reconstruction methods assume that there is a
single underlying tree topology for all sites along the sequence. The
presence of mosaic sequences due to recombination violates this assumption
and will cause phylogenetic methods to give misleading results due to the
imposition of a single tree topology on all sites. The detection of mosaic
sequences caused by recombination is therefore an important first step in
phylogenetic analysis. A graphical method for the detection of
recombination, based on the least squares method of phylogenetic
estimation, is presented here. This method locates putative recombination
breakpoints by moving a window along the sequence. The performance of the
method is assessed by simulation and by its application to a real data set.
相似文献
55.
Ana V. Coelho Pedro Matias Vilmos Fülöp Andrew Thompson A. Gonzalez M. A. Carrondo 《Journal of biological inorganic chemistry》1997,2(6):680-689
The structure of desulfoferrodoxin (DFX), a protein containing two mononuclear non-heme iron centres, has been solved by the MAD method using phases determined at 2.8?Å resolution. The iron atoms in the native protein were used as the anomalous scatterers. The model was built from an electron density map obtained after density modification and refined against data collected at 1.9?Å. Desulfoferrodoxin is a homodimer which can be described in terms of two domains, each with two crystallographically equivalent non-heme mononuclear iron centres. Domain I is similar to desulforedoxin with distorted rubredoxin-type centres, and domain II has iron centres with square pyramidal coordination to four nitrogens from histidines as the equatorial ligands and one sulfur from a cysteine as the axial ligand. Domain I in DFX shows a remarkable structural fit with the DX homodimer. Furthermore, three β-sheets extending from one monomer to another in DFX, two in domain I and one in domain II, strongly support the assumption of DFX as a functional dimer. A calcium ion, indispensable in the crystallisation process, was assumed at the dimer interface and appears to contribute to dimer stabilisation. The C-terminal domain in the monomer has a topology fold similar to that of fibronectin III. 相似文献
56.
Summary A lactic starter culture of a flocculentLactobacillus plantarum was produced in a fluidized bed reactor with higher cell volumetric productivities than in a continuous stirred tank reactor. The fluidized bed reactor was operated at optimised parameters obtained in batch reactor performed with and without pH control. 相似文献
57.
Pedro M. Matias Lígia M. Saraiva Cláudio M. Soares Ana V. Coelho Jean LeGall Maria Arménia Carrondo 《Journal of biological inorganic chemistry》1999,4(4):478-494
A monomeric nine-haem cytochrome c (9Hcc) with 292 amino acid residues was isolated from cells of the sulfate- and nitrate-reducing bacterium Desulfovibrio desulfuricans ATCC 27774 grown under both nitrate- and sulfate-respiring conditions. The nucleotide sequence encoding the 292 residues was determined, allowing the correction of about 10% of the previous primary structure, determined from 1.8?Å electron density maps. The refinement at 1.8?Å resolution of the structural model was completed, giving an R-value of 16.5%. The nine haem groups are arranged into two tetrahaem clusters, located at both ends of the molecule, with Fe-Fe distances and local protein fold very similar to tetrahaem cytochromes c 3, and the extra haem is located asymmetrically between the two regions. The new primary sequence determination confirmed the 39% sequence homology found between this cytochrome and the C-terminal region (residues 229–514) of the high-molecular-weight cytochrome c (Hmc) from D. vulgaris Hildenborough, providing strong evidence of structural similarity between 9Hcc and the C-terminal region of Hmc. The interaction between 9Hcc and the tetrahaem cytochrome c 3 from the same organism was studied by modelling methods, and the results suggest that a specific interaction is possible between haem 4 of tetrahaem cytochrome c 3 and haem 1 or haem 2 of 9Hcc, in agreement with previous kinetic experiments which showed the catalytic effect of the tetrahaem cytochrome c 3 upon the reduction of 9Hcc by the [NiFe] hydrogenase from D. desulfuricans ATCC 27774. These studies suggest a role for 9Hcc as part of the assembly of redox proteins involved in recycling the molecular hydrogen released by the cell as a result of substrate oxidation. 相似文献
58.
Alomá Moreno O y MJ Freuler 《Phyton》2015,84(2):466-472
The present study of the Orchidaceae family was carried out in Guamuahaya’s mountain range, from 2000 to March 2013. Fifteen districts were explored after 33 expeditions in the Province of Cienfuegos. Ninety two plant species were identified in the studied area, taking into account the ecological parameters of the mountainous areas of Cienfuegos and Cumanayagua municipalities. 相似文献
59.
60.
Susan C Burleigh Teun van de Laar Corné JM Stroop Wout MJ van Grunsven Niaobh O’Donoghue Pauline M Rudd Gavin P Davey 《BMC biotechnology》2011,11(1):1-17