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- Sandén, Anna Maria, et al.
(författare)
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Limiting factors in Escherichia coli fed-batch production of recombinant proteins
- 2003
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Ingår i: Biotechnology and Bioengineering. - : Wiley. - 0006-3592 .- 1097-0290. ; 81:2, s. 158-166
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Tidskriftsartikel (refereegranskat)abstract
- Fed-batch production of recombinant beta-galactosidase in E. coli was studied with respect to the specific growth rate at induction. The cultivations were designed to induce protein production by IPTG at a glucose feed rate corresponding to high (mu = 0.5 h(-1)) or low (mu = 0.1 h(-1)) specific growth rate. Protein production rate was approximately 100% higher at the higher specific growth rate, resulting in the accumulation of beta-galactosidase up to 30% of the total cell protein. Transcription analysis showed that beta-galactosidase-specific messenger RNA was immediately formed after induction (<5 min), but the amount was the same in both cases and was thus not the initial limiting factor. The content of ribosomes, as represented by rRNA, rapidly decreased with specific growth rate from a relative level of 100%, at the high specific growth rate, to 20% at the low specific growth rate. At high specific growth rate, ribosomes were additionally degraded upon induction due to the high production level. Translation therefore seemed to be the initial limiting factor of the protein synthesis capacity. The alarmone guanosine tetraphosphate increased at both high and low feed level inductions, indicating an induction-forced starvation of charged tRNA and/or glucose. The altered physiological status was also detected by the formation of acetic acid. However, the higher production rate resulted in high-level accumulation of acetic acid, which was absent at low feed rate production. Acetic acid production is thus coupled to the high product formation rate and is proposed to be due either to a precursor drain of Krebs cycle intermediates and a time lag before induction of the glyoxalate shunt, or to single amino acid overflow, since the model product is relatively poor in glycin and alanin. In conclusion, it is proposed that production at high specific growth rate becomes precursor-limited, while production at low specific growth rate is carbon- and/or energy-limited.
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- Reeh, S., et al.
(författare)
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Elastic properties of fcc Fe-Mn-X (X=Cr, Co, Ni, Cu) alloys from first-principles calculations
- 2013
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 87:22
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the valence electron concentration of X in fcc Fe-Mn-X (X=Cr, Co, Ni, Cu) alloys on the elastic and magnetic properties has been studied by means of ab initio calculations for alloy element concentrations of up to 8 at. % X. We observe that Cu increases the bulk-to-shear modulus (B/G) ratio by 19.2%. Simultaneously magnetic moments of Fe and Mn increase strongly. The other alloying elements induce less significant changes in B/G. The trends in B/G may be understood by considering the changes in G induced by the variation in valence electron concentration (VEC). As the VEC is increased, more pronounced metallic bonds are formed, giving rise to smaller shear modulus values. The changes in magnetic moments may be explained by the magnetovolume effect. Alloys with smaller VEC as Fe-Mn exhibit a decrease in local magnetic moments and equilibrium lattice parameters, while alloys with larger VEC as Fe-Mn demonstrate an increase in local magnetic moments and equilibrium lattice parameters. These data provide the basis for the design of Mn-rich steels with enhanced elastic properties.
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- Reeh, S, et al.
(författare)
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Elastic properties of fcc Fe-Mn-X (X = Cr, Co, Ni, Cu) alloys studied by the combinatorial thin film approach and ab initio calculations
- 2013
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Ingår i: Journal of Physics. - : Institute of Physics: Hybrid Open Access. - 0953-8984 .- 1361-648X. ; 25:24
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Tidskriftsartikel (refereegranskat)abstract
- The elastic properties of fcc Fe-Mn-X (X = Cr, Co, Ni, Cu) alloys with additions of up to 8 at.% X were studied by combinatorial thin film growth and characterization and by ab initio calculations using the disordered local moments (DLM) approach. The lattice parameter and Youngs modulus values change only marginally with X. The calculations and experiments are in good agreement. We demonstrate that the elastic properties of transition metal alloyed Fe-Mn can be predicted by the DLM model.
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