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1.
The problem of feedback optimization of the feed rate for fed-batch fermentation processes is formulated in the framework of singular control theory and switching hypersurfaces. Using four differential balance equations that describe a general class of fedbatch processes and a general objective function to be minimized, it is shown that under certain restrictions the feedback optimization of the feed rate can be realized as a nonlinear function of the state variables, such as the concentrations of cell mass, substrate and product, and the fermentor volume. The restrictions on the initial conditions, the fermentation kinetics and the objective function, that are needed for realization of the feedback optimization, are provided. Fed-batch fermentation models of lysine and alcohol are used to construct switching curves and to illustrate the feedback optimization of the feed flow rates. 相似文献
2.
Determination of the optimal feed rate for fed-batch fermentation is normally a problem in singular control with a state inequality constraint and as such is, in general, difficult to solve, especially for those described by a large number of dynamic mass balance equations. In this article we use a new set of state variables and the culture volume as the control variable. In this way the problem is converted to one of nonsingular control with the magnitude and rate constraints on the manipulated variable and can be numerically solved by a gradient-based technique, thus avoiding the difficulty associated with singular control problems. Examples are given to illustrate the method. 相似文献
3.
Inactivation of Escherichia coli DNA polymerase I by pyridoxal 5'-phosphate treatment results from its reactivity at multiple lysine residues. One of these residues, lysine-758, has been shown to be located at the substrate binding site in DNA polymerase I [Basu, A., & Modak, M. J. (1987) Biochemistry 26, 1704-1709]. We now demonstrate that lysine-635 is another important target of pyridoxylation; modification of this site results in decreased rates of DNA synthesis. Addition of template-primer with or without substrate deoxynucleoside triphosphate protects lysine-635 from pyridoxylation. Analysis of the initiation versus elongation phase of DNA synthesis by lysine-635-modified enzyme revealed that elongation of the DNA chain is severely affected by the lysine-635 modification. We therefore conclude that this lysine residue plays an important role in the processive mode of DNA synthesis by E. coli DNA polymerase I. 相似文献
4.
A complete three-dimensional structure of the Klenow fragment of Escherichia coli DNA polymerase I (pol I) has been proposed on the basis of molecular modeling and molecular mechanics studies using available C alpha coordinates. The structure seems quite reliable because the overall surface of electrostatic potentials calculated for the molecularly modeled enzyme closely resembles that reported for the X-ray structure. The modeled structure is then used in developing a ternary complex of dTTP and (dA)25-(dT)14 poised in its active site. The orientation of both substrates in the ternary complex was primarily guided by the amino acid residues which had been known to interact with dNTP and DNA substrates from earlier studies. The proposed model (a) explains the geometrical and physicochemical relationship of the two substrates with the various critical amino acid residues involved in the binding process and (b) suggests possible roles for additional residues in the binding and/or polymerization reaction. Furthermore, the ternary complex appears to satisfy many biochemical and genetic data concerning catalytic requirements known to exist for the polymerization reaction. 相似文献
5.
Photolithoautotrophic growth and control of CO2 fixation in Rhodobacter sphaeroides and Rhodospirillum rubrum in the absence of ribulose bisphosphate carboxylase-oxygenase. 总被引:1,自引:1,他引:0
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Rhodospirillum rubrum and Rhodobacter sphaeroides were shown to be capable of photolithoautotrophic growth in the absence of the reductive pentose phosphate (Calvin) cycle. Ribulose 1,5-bisphosphate carboxylase-oxygenase (RubisCO) deletion strains were incapable of photolithoautotrophic growth using hydrogen as an electron donor but were able to grow in the absence of organic carbon using less reduced inorganic electron donors, i.e., thiosulfate or sulfide. Wild-type R. rubrum grown in the presence of thiosulfate contained RubisCO levels that were 50-fold lower compared with those in cells growth with hydrogen as an electron donor without substantially influencing rates of photolithoautotrophic growth. These results suggest there are two independent CO2 fixation pathways that support photolithoautotrophic growth in purple nonsulfur photosynthetic bacteria, indicating that these organisms have developed sophisticated control mechanisms to regulate the flow of carbon from CO2 through these separate pathways. 相似文献
6.
Shrihari Bhavaraju SR Modak JM Kumar R Gandhi KS 《Biotechnology and bioengineering》1993,41(6):612-616
The growth of Thiobacillus ferrooxidans on sulphur is known to proceed through the attachment of cells to the sulphur particles. Experiments, However, show that the cells in the liquid phase, which are not attached to the sulphur particles, also grow. It has been shown through the use of a two-compartment membrane reactor that this increase is partially due to the release of ions, corresponding to partially oxidized of sulphur, into the solution by the attached cells. The main soluble ion has been found to the thiosulphate, but traces of sulphite have also been detected. (c) 1993 John Wiley & Sons, Inc. 相似文献
7.
8.
S L Marcus S W Smith C I Jarowski M J Modak 《Biochemical and biophysical research communications》1976,70(1):37-44
Guanosine, rather than its methylated derivative, was found to be the inverted nucleoside present in the 5′ terminal capping structure of insect oocyte messenger RNA. Since methylation of the terminal guanosine at the 7 position is necessary for the initiation of protein synthesis in eukaryotes, this evidence suggests that the translational inactivity of the mRNA prior to fertilization may be associated with the absence of methylation. 相似文献
9.
Chromatin prepared using micrococcal nuclease retains the enzyme activity which can be removed with cation-exchange resin AG 50 WX2.
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Micrococcal nuclease used to digest nuclei remains bound to the chromatin in an inactive form. The enzyme activity can be restored in situ by addition of divalent cations such as Ca++ or Mg++ resulting in continued digestion of high molecular weight chromatin into smaller fragments as demonstrated by two dimensional gel electrophoresis of samples as chromatin and DNA in the first and second dimensions, respectively. The bound enzyme can be selectively removed from the chromatin by treatment with cation exchange resin AG 50 WX2 at low salt concentration without altering the electrophoretic mobility of the chromatin. 相似文献
10.
Somnath Mahato Arup Ghorai Sanjeev Kumar Srivastava Mantu Modak Sudarshan Singh Samit K. Ray 《Liver Transplantation》2020,10(30)
The synthesis of single‐crystalline β‐CsPbI3 perovskite nanorods (NRs) using a colloidal process is reported, exhibiting their improved photostability under 45–55% humidity. The crystal structure of CsPbI3 NRs films is investigated using Rietveld refined X‐ray diffraction (XRD) patterns to determine crystallographic parameters and the phase transformation from orthorhombic (γ‐CsPbI3) to tetragonal (β‐CsPbI3) on annealing at 150 °C. Atomic resolution transmission electron microscopy images are utilized to determine the probable atomic distribution of Cs, Pb, and I atoms in a single β‐phase CsPbI3 NR, in agreement with the XRD structure and selected area electron diffraction pattern, indicating the growth of single crystalline β‐CsPbI3 NR. The calculation of the electronic band structure of tetragonal β‐CsPbI3 using density functional theory (DFT) reveals a direct transition with a lower band gap and a higher absorption coefficient in the solar spectrum, as compared to its γ‐phase. An air‐stable (45–55% humidity) inverted perovskite solar cell, employing β‐CsPbI3 NRs without any encapsulation, yields an efficiency of 7.3% with 78% enhancement over the γ‐phase, showing its potential for future low cost photovoltaic devices. 相似文献