| 1. |
- Bohlin, Christina, et al.
(författare)
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Oxidation of the erythro and threo forms of the phenolic lignin model compound 1-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol by laccases and model oxidants
- 2009
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Ingår i: Bioorganic chemistry (Print). - : Elsevier. - 0045-2068 .- 1090-2120. ; 37:5, s. 143-148
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Tidskriftsartikel (refereegranskat)abstract
- Mixtures of equal amounts of the erythro and threo forms of the phenolic arylglycerol β-aryl ether 1-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol were oxidized (i) with laccases from Trametes versicolor, Agaricus bisporus, Myceliophthora thermophila and Rhus vernicifera, (ii) with laccase-mediator systems consisting of T. versicolor laccase and ABTS or HBT, and (iii) with various model oxidants including cerium(IV) ammonium nitrate (CAN), lignin peroxidase, Fenton’s reagent, and lead(IV) tetraacetate (LTA). All the laccases exhibited a similar preferential degradation of the threo form. The mediator ABTS counteracted the threo preference of laccase, but the mediator HBT did not affect it. The outer-sphere model oxidants CAN and lignin peroxidase showed a preferential degradation of the threo form. LTA and Fenton’s reagent did not exhibit any stereo-preference. The results suggest that laccases of different origin, primary structure, and redox potential behave as typical outer-sphere oxidants in their interaction with the diastereomers of the arylglycerol β-aryl ether
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| 2. |
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| 3. |
- Sevastik, Robin, et al.
(författare)
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Quantum chemical modeling of enzymatic reactions : the case of 4-oxalocrotonate tautomerase
- 2007
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Ingår i: Bioorganic chemistry (Print). - : Elsevier BV. - 0045-2068. ; 35:6, s. 444-457
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Tidskriftsartikel (refereegranskat)abstract
- The reaction mechanism of 4-oxalocrotonate tautomerase (4-OT) is studied using the density functional theory method B3LYP. This enzyme catalyzes the isomerisation of unconjugated alpha-keto acids to their conjugated isomers. Two different quantum chemical models of the active site are devised and the potential energy curves for the reaction are computed. The calculations support the proposed reaction mechanism in which Pro-1 acts as a base to shuttle a proton from the C3 to the C5 position of the substrate. The first step (proton transfer from C3 to proline) is shown to be the rate-limiting step. The energy of the charge-separated intermediate (protonated proline-deprotonated substrate) is calculated to be quite low, in accordance with measured pK(a) values. The results of the two models are used to evaluate the methodology employed in modeling enzyme active sites using quantum chemical cluster models.
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| 4. |
- Shleev, Sergey, et al.
(författare)
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Characterization of two new multiforms of Trametes pubescens laccase
- 2007
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Ingår i: Bioorganic Chemistry. - : Elsevier BV. - 0045-2068. ; 35:1, s. 35-49
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Tidskriftsartikel (refereegranskat)abstract
- Electrochemical properties of two multiforms of laccase from Trametes pubescens basidiomycete (LACI and LAC2) have been studied. The standard redox potentials of the T1 sites of the enzymes were found to be 746 and 738 mV us. NHE for LACI and LAC2, respectively. Bioelectroreduction of oxygen based on direct electron transfer between each of the two forms of Trametes pubescens laccase and spectrographic graphite electrodes has been demonstrated and studied. It. is concluded that the T1 site of laccase is the first electron acceptor, both in solution (homogeneous case) and when the enzymes are adsorbed on the surface of the graphite electrode (heterogeneous case). Thus, the previously proposed mechanism of oxygen bioelectroreduction by adsorbed fungal laccase was additionally confirmed using two forms of the enzyme. Moreover, the assumed need for extracellular laccase to communicate directly and electronically with a solid matrix (lignin) in the course of lignin degradation is discussed. In summary, the possible roles of multiforms of the enzyme based on their electrochemical, biochemical, spectral, and kinetic properties have been suggested to consist in broadening of the substrate specificity of the enzyme, in turn yielding the possibility to dynamically regulate the process of lignin degradation according to the real-time survival needs of the organism.
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