| 31. |
- Adlercreutz, Patrick, et al.
(författare)
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Oxygen supply to immobilized cells - 4. Use of p-benzoquinone as an oxygen substitute
- 1984
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Ingår i: Applied Microbiology and Biotechnology. - 0175-7598. ; 20:5, s. 296-302
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen supply is a critical point in technical processes when aerobic cells are used in immobilized preparations. In this study p-benzoquinone is used as a substitute for oxygen in the oxidation of glycerol to dihydroxyacetone by immobilized Gluconobacter oxydans cells. The reaction rate was much higher when p-benzoquinone was used compared to when oxygen was used. In an experiment with free cells p-benzoquinone gave a rate more than four times that of oxygen, and with immobilized cells the difference was even greater. p-benzoquinone is more effective than oxygen because it gives a higher maximal reaction rate (the reason for this fact is discussed) and because it is more soluble in water than oxygen. The operational stability of the process is comparatively good. In one experiment the productivity decreased from 60 to 10 mmol/h·g over an 8-day period when p-benzoquinone was used. When oxygen was used in a similar experiment the productivity decreased from 14 to 6 mmol/h·g. The byproduct formed from p-benzoquinone, hydroquinone, can be oxidized to p-benzoquinone which can be re-used. Seven succesive regenerations of p-benzoquinone were performed without any loss of efficiency.
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| 32. |
- Adlercreutz, Patrick
(författare)
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Oxygen supply to immobilized cells : 5. Theoretical calculations and experimental data for the oxidation of glycerol by immobilized Gluconobacter oxydans cells with oxygen or p‐benzoquinone as electron acceptor
- 1986
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Ingår i: Biotechnology and Bioengineering. - : Wiley. - 0006-3592 .- 1097-0290. ; 28:2, s. 223-232
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Tidskriftsartikel (refereegranskat)abstract
- Theoretical calculations of reaction kinetics were done for one‐step reactions catalyzed by cells immobilized in spherical beads. The reactions catalyzed by free cells were assumed to obey Michaelis–Menten kinetics for a one‐substrate reaction. Both external (outside the beads) and internal (inside the beads) mass transfer of the substrate were considered for the immobilized preparations. The theoretical calculations were compared with experimental data for the oxidation of glycerol to dihydroxyacetone by Gluconobacter oxydans cells immobilized in calcium alginate gel. Glycerol was present in excess so that the reaction rate was limited by oxygen. The correlation between experimental data and theoretical calculations was quite good. The calculations showed how the overall effectiveness factor was influenced by, for example, the particle size and the cell density in the beads. In most cases the reaction rate was mainly limited by internal mass transfer of the substrate (oxygen). As shown previously, p‐benzoquinone can replace oxygen as the electron acceptor in this reaction. The same equations for reaction kinetics and mass transfer were used with p‐benzoquinone as the rate‐limiting substrate. Parameters such as diffusivity, maximal reaction rate, and K were, of course, different. In this case also, the correlation between the model and the experimental results was quite good. Much higher production rates were obtained with p‐benzoquinone as the electron acceptor compared to when oxygen was used. The reasons for this fact were that p‐benzoquinone gave a higher maximal reaction rate for free cells and the solubility of p‐benzoquinone was higher than for oxygen. Different methods of increasing the rate of microbial oxidation reactions are discussed.
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| 33. |
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| 34. |
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| 35. |
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| 36. |
- Adlercreutz, Patrick
(författare)
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Use of artificial electron acceptors in oxidation reactions catalyzed by acetic acid bacteria
- 1987
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Ingår i: Biotechnology Techniques. - 0951-208X. ; 1:2, s. 103-108
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Tidskriftsartikel (refereegranskat)abstract
- The ability of several electron acceptors to promote the Gluconobacter oxydans catalyzed oxidation of glycerol was investigated. p-Benzoquinone was the most effective electron acceptor. The reaction rate obtained with p-benzoquinone was higher than the maximal rate with the natural electron acceptor, oxygen, in all the oxidation reactions tested.
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| 37. |
- Aevarsson, A, et al.
(författare)
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Ligands to the 2Fe iron-sulfur center in succinate dehydrogenase
- 1988
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Ingår i: FEBS Letters. - : Wiley. - 1873-3468 .- 0014-5793. ; 232:2, s. 298-302
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Tidskriftsartikel (refereegranskat)abstract
- Membrane-bound succinate oxidoreductases are flavoenzymes containing one each of a 2Fe, a 3Fe and a 4Fe iron-sulfur center. Amino acid sequence homologies indicate that all three centers are located in the Ip (B) subunit. From polypeptide and gene analysis of Bacillus subtillis succinate dehydrogenase-defective mutants combined with earlier EPR spectroscopic data, we show that four conserved cysteine residues in the first half of Ip are the ligands to the [2Fe-2S] center. These four residues have previously been predicted to be the ligands. Our results also suggest that the N-terminal part of B. subtilis Ip constitutes a domain which can incorporate separately the 2Fe center and interact with Fp, the flavin-containing subunit of the dehydrogenase.
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| 38. |
- Agardh, Carl-David, et al.
(författare)
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Desensitisation as a means of preventing untoward reactions to ionic contrast media
- 1983
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Ingår i: Acta Radiologica Diagnosis. - 0567-8056. ; 24:3, s. 235-239
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Tidskriftsartikel (refereegranskat)abstract
- Patients with a previous history of anaphylactic reactions to ionic iodinated contrast media were desensitised before a second radiologic examination was performed. The tolerance to the contrast medium was raised by repeated intravenous injections in increasing doses and concentrations. No serious side effects were noted when the examinations with contrast medium was repeated within a few days after the desensitisation. The positive effect of the desensitisation may depend on a successive consumption of complement proteins, probably responsible for the allergic reactions. Therefore, the available amount of complement for some days may be too low for the occurrence of a complement reaction.
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| 39. |
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| 40. |
- Agardh, Carl-David, et al.
(författare)
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Diabetic control in community care. The use of clinical evaluation and hemoglobin A1
- 1985
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Ingår i: Scandinavian Journal of Primary Health Care. - : Informa UK Limited. - 0281-3432 .- 1502-7724. ; 3:1, s. 15-18
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Tidskriftsartikel (refereegranskat)abstract
- Diabetic control was evaluated in 50 consecutive patients attending a community care centre, either by clinical criteria or by determination of glycosylated hemoglobin (HbA1). Two methods used for the determination of HbA1 were found to give similar results, namely ion exchange chromatography and agar gel electrophoresis. On a group basis, good correlation was observed between HbA1 samples analysed prior to and following the elimination of the labile HbA1 fraction. When comparing three treatment modes (diet alone, hypoglycemic agents or insulin), no significant differences in HbA1 levels were noted. Patients considered to have satisfactory and poor control had significantly higher HbA1 levels than those considered to have good control, while no differences were seen between those considered to have satisfactory or poor control. It is concluded that the methods described for the determination of HbA1 yield similar results. Clinical evaluation of diabetic control is reliable in patients classified to have good or poor control. However, in many patients who are considered to have satisfactory control, regular determinations of HbA1 provide valuable additional information.
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