Radical scavenging and electron-transfer reactions in Polyporus Versicolor laccase: A pulse radiolysis study |
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Authors: | Annie Guissani Yann Henry Lucien Gilles |
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Affiliation: | 1. Laboratoire de Biophysique, Institut de Biologie Physico-chimique, 13, rue Pierre el Marie Curie, 75005 ParisFrance;2. Division physico-chimique, Section de Chimie moléculaire, Centre d''Etudes Nucléaires de Saclay, 91191 Gif-sur-Yvette Cedex, France |
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Abstract: | The interaction of the radicals OH?, t-BuO?, eaq?, CO2XXX and O2XXX with the copper oxidase. laccase. from Polyporus, has been studied by the pulse-radiolysis technique. Each of these radicals formed transient adducts with a broad absorption maximum around 310 nm. Analysis of the optical properties and of the very fast rates of formation of these compounds shows that each radical interacts with a limited number of sites on the polypeplide part of the protein amongst R-S-S-R. histidine and aromatic residues. Interaction with the carbonyl group of some of the peptide bonds is also possible. The few target sites are probably hit simultaneously and electron transfer between these sites may also occur. In all cases, in a subsequent step, intramolecular electron transfer from the polypeptide radical adducts leads to a partial reduction of the blue type-1 Cu2+ with rates varying between 103 and 104 s?1. Further reduction of the type-1 Cu2+ occurs through a slow intermolecular reaction between two laccase radical transient adducts. In the case of COXXX2 and OXXX2, this slow reduction could alternatively be due to an intermolecular reaction between laccase and COXXX2 or OXXX2. The oxidant radicals OH?. BrXXX2 and (SCN)XXX2, which formed radical adducts with fully ascorbate-reduced laccase, did not induce any type-1 copper reoxidation. |
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Keywords: | Electron transfer Pulse radiolysis Radical scavenging Laccase |
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