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- Sárvári Horváth, Ilona, 1960, et al.
(författare)
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Effects of furfural on the respiratory metabolism of Saccharomyces cerevisiae in glucose-limited chemostats
- 2003
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Ingår i: Applied and Environmental Microbiology. - 0099-2240 .- 1098-5336. ; 69:7, s. 4076-4086
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Tidskriftsartikel (refereegranskat)abstract
- Effects of furfural on the aerobic metabolism of the yeast Saccharomyces cerevisiae were studied by performing chemostat experiments, and the kinetics of furfural conversion was analyzed by performing dynamic experiments. Furfural, an important inhibitor present in lignocellulosic hydrolysates, was shown to have an inhibitory effect on yeast cells growing respiratively which was much greater than the inhibitory effect previously observed for anaerobically growing yeast cells. The residual furfural concentration in the bioreactor was close to zero at all steady states obtained, and it was found that furfural was exclusively converted to furoic acid during respiratory growth. A metabolic flux analysis showed that furfural affected fluxes involved in energy metabolism. There was a 50% increase in the specific respiratory activity at the highest steady-state furfural conversion rate. Higher furfural conversion rates, obtained during pulse additions of furfural, resulted in respirofermentative metabolism, a decrease in the biomass yield, and formation of furfuryl alcohol in addition to furoic acid. Under anaerobic conditions, reduction of furfural partially replaced glycerol formation as a way to regenerate NAD+. At concentrations above the inlet concentration of furfural, which resulted in complete replacement of glycerol formation by furfuryl alcohol production, washout occurred. Similarly, when the maximum rate of oxidative conversion of furfural to furoic acid was exceeded aerobically, washout occurred. Thus, during both aerobic growth and anaerobic growth, the ability to tolerate furfural appears to be directly coupled to the ability to convert furfural to less inhibitory compounds.
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| 2. |
- Taherzadeh Esfahani, Mohammad, 1965, et al.
(författare)
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Continuous Cultivation of Dilute-Acid Hydrolysates to Ethanol by Immobilized Saccharomyces cerevisiae
- 2001
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Ingår i: Applied Biochemistry and Biotechnology. - 0273-2289 .- 1559-0291. ; 95:1, s. 45-57
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Tidskriftsartikel (refereegranskat)abstract
- The continuous cultivation of immobilized Saccharomyces cerevisiae CBS 8066 on dilute-acid hydrolysates of forest residuals was investigated. The yeast cells were immobilized in 2–4% Ca-alginate beads. The 2% beads were not stable. However, the 3 and 4% beads were stable for at least 3 wk when an extra resource of calcium ions was available in the medium. The continuous cultivation of a dilute-acid hydrolysate by the immobilized cells at dilution rates of 0.3, 0.5, and 0.6 h−1 resulted in 86, 83, and 79% sugar consumption, respectively, and an ethanol yield between 0.45 and 0.48 g/g. The hydrolysate was fermentable at a dilution rate of 0.1 h−1 in a free-cell system but washed out at a dilution rate of 0.2 h−1. The continuous cultivation of a more inhibiting hydrolysate was not successful by either free- or immobilized-cell systems even at a low dilution rate of 0.07 h−1. However, when the hydrolysate was overlimed, it was fermentable by the immobilized cells at a dilution rate of 0.2 h−1.
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| 6. |
- Dincbas-Renqvist, Vildan, et al.
(författare)
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Thermodynamics of folding, stabilization, and binding in an engineered protein--protein complex.
- 2004
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 126:36, s. 11220-30
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Tidskriftsartikel (refereegranskat)abstract
- We analyzed the thermodynamics of a complex protein-protein binding interaction using the (engineered) Z(SPA)(-)(1) affibody and it's Z domain binding partner as a model. Free Z(SPA)(-)(1) exists in an equilibrium between a molten-globule-like (MG) state and a completely unfolded state, wheras a well-ordered structure is observed in the Z:Z(SPA)(-)(1) complex. The thermodynamics of the MG state unfolding equilibrium can be separated from the thermodynamics of binding and stabilization by combined analysis of isothermal titration calorimetry data and a separate van't Hoff analysis of thermal unfolding. We find that (i) the unfolding equilibrium of free Z(SPA)(-)(1) has only a small influence on effective binding affinity, that (ii) the Z:Z(SPA)(-)(1) interface is inconspicuous and structure-based energetics calculations suggest that it should be capable of supporting strong binding, but that (iii) the conformational stabilization of the MG state to a well-ordered structure in the Z:Z(SPA)(-)(1) complex is associated with a large change in conformational entropy that opposes binding.
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| 8. |
- Gustafsson, Susanne, 1962-
(författare)
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Population genetic analyses in the orchid genus Gymnadenia : a conservation genetic perspective
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Small populations are facing a particular risk of extinction due to a lack of appropriate genetic diversity and associated negative effects, factors dealt with in the discipline of conservation genetics. Many orchid species exhibit characteristics that make them a perfect study object in the scope of conservation genetics. The aim with this thesis was to investigate genetic structure at different levels in two orchid species Gymnadenia conopsea, geographically widespread, although diminishing and G. odoratissima with a long history of being rare. Microsatellite markers, developed in and used in studies of G. conopsea were also used in the study of G. odoratissima.Populations of G. conopsea expressed high levels of genetic variation and a certain amount of gene flow, although investigated mating pattern in a small population indicated non-random mating among individuals, with the majority of pollen exchange between near neighbours, and noticeable levels of geitonogamous pollinations. Further a pronounced year to year variation in flowering frequency among individuals was found. It was also discovered that flowering time variants (early and late) within the species G. conopsea were highly differentiated and seem to have had a more ancient historical separation than the separation between the two different species, G. conopsea and G. odoratissima. Levels of genetic variation in the rare congener, G. odoratissima differed between island and mainland populations where the more numerous island populations expressed larger levels of genetic variation and were less differentiated compared to the few remaining and genetically depauperated mainland populations.Uppsala University Library, Box 510, 75120, Uppsala, Sweden
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| 10. |
- Lendel, Christofer, et al.
(författare)
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Biophysical characterization of Z(SPA-1)--a phage-display selected binder to protein A.
- 2004
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Ingår i: Protein science : a publication of the Protein Society. - : Wiley. - 0961-8368 .- 1469-896X. ; 13:8, s. 2078-88
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Tidskriftsartikel (refereegranskat)abstract
- Affibodies are a novel class of binding proteins selected from phagemid libraries of the Z domain from staphylococcal protein A. The Z(SPA-1) affibody was selected as a binder to protein A, and it binds the parental Z domain with micromolar affinity. In earlier work we determined the structure of the Z:Z(SPA-1) complex and noted that Z(SPA-1) in the free state exhibits several properties characteristic of a molten globule. Here we present a more detailed biophysical investigation of Z(SPA-1) and four Z(SPA-1) mutants with the objective to understand these properties. The characterization includes thermal and chemical denaturation profiles, ANS binding assays, size exclusion chromatography, isothermal titration calorimetry, and an investigation of structure and dynamics by NMR. The NMR characterization of Z(SPA-1) was facilitated by the finding that trimethylamine N-oxide (TMAO) stabilizes the molten globule conformation in favor of the fully unfolded state. All data taken together lead us to conclude the following: (1) The topology of the molten globule conformation of free Z(SPA-1) is similar to that of the fully folded structure in the Z-bound state; (2) the extensive mutations in helices 1 and 2 destabilize these without affecting the intrinsic stability of helix 3; (3) stabilization and reduced aggregation can be achieved by replacing mutated residues in Z(SPA-1) with the corresponding wild-type Z residues. This stabilization is better correlated to changes in helix propensity than to an expected increase in polar versus nonpolar surface area of the fully folded state.
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