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Xu F Kulys JJ Duke K Li K Krikstopaitis K Deussen HJ Abbate E Galinyte V Schneider P 《Applied and environmental microbiology》2000,66(5):2052-2056
1-Hydroxybenzotriazole, violuric acid, and N-hydroxyacetanilide are three N-OH compounds capable of mediating a range of laccase-catalyzed biotransformations, such as paper pulp delignification and degradation of polycyclic hydrocarbons. The mechanism of their enzymatic oxidation was studied with seven fungal laccases. The oxidation had a bell-shaped pH-activity profile with an optimal pH ranging from 4 to 7. The oxidation rate was found to be dependent on the redox potential difference between the N-OH substrate and laccase. A laccase with a higher redox potential or an N-OH compound with a lower redox potential tended to have a higher oxidation rate. Similar to the enzymatic oxidation of phenols, phenoxazines, phenothiazines, and other redox-active compounds, an "outer-sphere" type of single-electron transfer from the substrate to laccase and proton release are speculated to be involved in the rate-limiting step for N-OH oxidation. 相似文献
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Feng Xu Juozas J. Kulys Kyle Duke Kaichang Li Kastis Krikstopaitis Heinz-Josef W. Deussen Eric Abbate Vilija Galinyte Palle Schneider 《Applied microbiology》2000,66(5):2052-2056
1-Hydroxybenzotriazole, violuric acid, and N-hydroxyacetanilide are three N-OH compounds capable of mediating a range of laccase-catalyzed biotransformations, such as paper pulp delignification and degradation of polycyclic hydrocarbons. The mechanism of their enzymatic oxidation was studied with seven fungal laccases. The oxidation had a bell-shaped pH-activity profile with an optimal pH ranging from 4 to 7. The oxidation rate was found to be dependent on the redox potential difference between the N-OH substrate and laccase. A laccase with a higher redox potential or an N-OH compound with a lower redox potential tended to have a higher oxidation rate. Similar to the enzymatic oxidation of phenols, phenoxazines, phenothiazines, and other redox-active compounds, an “outer-sphere” type of single-electron transfer from the substrate to laccase and proton release are speculated to be involved in the rate-limiting step for N-OH oxidation. 相似文献
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Juozas Kulys Kastis Krikstopaitis Arturas Ziemys 《Journal of biological inorganic chemistry》2000,5(3):333-340
N -substituted phenothiazines (PTs) and phenoxazines (POs) catalyzed by fungal Coprinus cinereus peroxidase and Polyporus pinsitus laccase were investigated at pH 4–10. In the case of peroxidase, an apparent bimolecular rate constant (expressed as k
cat/K
m) varied from 1 ×107 M−1 s−1to 2.6×108 M−1 s−1 at pH 7.0. The constants for PO oxidation were higher in comparison to PT. pH dependence revealed two or three ionizable
groups with pK
a values of 4.9–5.7 and 7.7–9.7 that significantly affected the activity of peroxidase. Single-turnover experiments showed
that the limiting step of PT oxidation was reduction of compound II and second-order rate constants were obtained which were
consistent with the constants at steady-state conditions. Laccase-catalyzed PT and PO oxidation rates were lower; apparent
bimolecular rate constants varied from 1.8×105 M−1 s−1 to 2.0×107 M−1 s−1 at pH 5.3. PO constants were higher in comparison to PT, as was the case with peroxidase. The dependence of the apparent
bimolecular constants of compound II or copper type 1 reduction, in the case of peroxidase or laccase, respectively, was analyzed
in the framework of the Marcus outer-sphere electron-transfer theory. Peroxidase-catalyzed reactions with PT, as well as PO,
fitted the same hyperbolic dependence with a maximal oxidation rate of 1.6×108 M−1 s−1 and a reorganization energy of 0.30 eV. The respective parameters for laccase were 5.0×107 M−1 s−1 and 0.29 eV.
Received: 20 September 1999 / Accepted: 24 February 2000 相似文献
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