| 1001. |
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| 1002. |
- Powlowski, J, et al.
(författare)
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Genetics and biochemistry of phenol degradation by Pseudomonas sp. CF600.
- 1994
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Ingår i: Biodegradation. - 0923-9820 .- 1572-9729. ; 5:3-4
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Tidskriftsartikel (refereegranskat)abstract
- Pseudomonas sp. strain CF600 is an efficient degrader of phenol and methylsubstituted phenols. These compounds are degraded by the set of enzymes encoded by the plasmid located dmpoperon. The sequences of all the fifteen structural genes required to encode the nine enzymes of the catabolic pathway have been determined and the corresponding proteins have been purified. In this review the interplay between the genetic analysis and biochemical characterisation of the catabolic pathway is emphasised. The first step in the pathway, the conversion of phenol to catechol, is catalysed by a novel multicomponent phenol hydroxylase. Here we summarise similarities of this enzyme with other multicomponent oxygenases, particularly methane monooxygenase (EC 1.14.13.25). The other enzymes encoded by the operon are those of the well-known meta-cleavage pathway for catechol, and include the recently discovered meta-pathway enzyme aldehyde dehydrogenase (acylating) (EC 1.2.1.10). The known properties of these meta-pathway enzymes, and isofunctional enzymes from other aromatic degraders, are summarised. Analysis of the sequences of the pathway proteins, many of which are unique to the meta-pathway, suggests new approaches to the study of these generally little-characterised enzymes. Furthermore, biochemical studies of some of these enzymes suggest that physical associations between meta-pathway enzymes play an important role. In addition to the pathway enzymes, the specific regulator of phenol catabolism, DmpR, and its relationship to the XylR regulator of toluene and xylene catabolism is discussed.
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| 1003. |
- Powlowski, J, et al.
(författare)
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In vitro analysis of polypeptide requirements of multicomponent phenol hydroxylase from Pseudomonas sp. strain CF600.
- 1990
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Ingår i: Journal of Bacteriology. - 0021-9193 .- 1098-5530. ; 172:12
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Tidskriftsartikel (refereegranskat)abstract
- An in vitro study of the multicomponent phenol hydroxylase from Pseudomonas sp. strain CF600 was performed. Phenol-stimulated oxygen uptake from crude extracts was strictly dependent on the addition of NAD(P)H and Fe2+ to assay mixtures. Five of six polypeptides required for growth on phenol were necessary for in vitro activity. One of the polypeptides was purified to homogeneity and found to be a flavin adenine dinucleotide containing iron-sulfur protein with significant sequence homology, at the amino terminus, to plant-type ferredoxins. This component, as in other oxygenase systems, probably functions to transfer electrons from NAD(P)H to the iron-requiring oxygenase component. Phenol hydroxylase from this organism is thus markedly different from bacterial flavoprotein monooxygenases commonly used for hydroxylation of other phenolic compounds, but bears a number of similarities to multicomponent oxygenase systems for unactivated compounds.
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| 1004. |
- Powlowski, J, et al.
(författare)
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Purification and properties of the physically associated meta-cleavage pathway enzymes 4-hydroxy-2-ketovalerate aldolase and aldehyde dehydrogenase (acylating) from Pseudomonas sp. strain CF600.
- 1993
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Ingår i: Journal of Bacteriology. - 0021-9193 .- 1098-5530. ; 175:2
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Tidskriftsartikel (refereegranskat)abstract
- The final two steps in the dmp operon-encoded meta-cleavage pathway for phenol degradation in Pseudomonas sp. strain CF600 involve conversion of 4-hydroxy-2-ketovalerate to pyruvate and acetyl coenzyme A (acetyl-CoA) by the enzymes 4-hydroxy-2-ketovalerate aldolase and aldehyde dehydrogenase (acylating) [acetaldehyde:NAD+ oxidoreductase (CoA acetylating), EC 1.2.1.10]. A procedure for purifying these two enzyme activities to homogeneity is reported here. The two activities were found to copurify through five different chromatography steps and ammonium sulfate fractionation, resulting in a preparation that contained approximately equal proportions of two polypeptides with molecular masses of 35 and 40 kDa. Amino-terminal sequencing revealed that the first six amino acids of each polypeptide were those deduced from the previously determined nucleotide sequences of the corresponding dmp operon-encoded genes. The isolated complex had a native molecular mass of 148 kDa, which is consistent with the presence of two of each polypeptide per complex. In addition to generating acetyl-CoA from acetaldehyde, CoA, and NAD+, the dehydrogenase was shown to acylate propionaldehyde, which would be generated by action of the meta-cleavage pathway enzymes on the substrates 3,4-dimethylcatechol and 4-methylcatechol. 4-Hydroxy-2-ketovalerate aldolase activity was stimulated by the addition of Mn2+ and, surprisingly, NADH to assay mixtures. The possible significance of the close physical association between these two polypeptides in ensuring efficient metabolism of the short-chain aldehyde generated by this pathway is discussed.
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| 1005. |
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| 1006. |
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| 1007. |
- Puu, Tönu, 1936-
(författare)
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Chaos in business cycles
- 1991
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Ingår i: Chaos, Solitons & Fractals. - : Elsevier BV. - 0960-0779 .- 1873-2887. ; 1:5, s. 457-473
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Tidskriftsartikel (refereegranskat)abstract
- The business cycle is studied in terms of the mapping Zt = λZt−1 − (λ+1)Z3t−1 − σYt−1 Yt = Zt−1 + Y−1 where the variables Y, Z denote income and rate of income change respectively, and λ, σ are two structural parameters. The model produces chaotic or periodic output for income differences. For small σ income acts as a slow feed back causing bifurcations between periodic and chaotic behaviour over the cycle. Typically, transitions between prosperity and depression set in with chaos after which there follows a period halving route to order.
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| 1008. |
- Puu, Tönu, 1936-
(författare)
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Chaos in duopoly pricing
- 1991
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Ingår i: Chaos, Solitons & Fractals. - 0960-0779 .- 1873-2887. ; 1:6, s. 573-581
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of two competing firms in a market is studied in terms of Cournot's duopoly theory. Assuming iso-elastic demand and constant unit production costs the iterative mapping for the outputs of the two firms ensues. The two constants are the unit production costs. The fixed point, the Cournot equilibrium, has earlier been assumed to be the only interesting feature of this model. It is, however, shown that the model can produce persistent motion, periodic or chaotic.
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| 1009. |
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| 1010. |
- Puu, Tönu, 1936-
(författare)
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Hotelling's migration model revisited
- 1991
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Ingår i: Environment and planning A. - 0308-518X .- 1472-3409. ; 23:8, s. 1209-1216
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Tidskriftsartikel (refereegranskat)abstract
- In the present article Hotelling's model of population growth and migration of 1921 is 'revisited'. After a discussion of the stationary solutions and their stability the main point is made. The model itself is structurally unstable, but can be easily stabilized by adding a simple autonomous migration component. By this, the solution curves, in the shape of constant amplitude population waves over space for the original model, either become damped in one direction and explosive in another or are replaced by just one single spatial limit cycle.
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