Oxidation of hydroquinones by the versatile ligninolytic peroxidase from Pleurotus eryngii. H2O2 generation and the influence of Mn2+.
Formation of H2O2 during the oxidation of three lignin-derived hydroquinones by the ligninolytic versatile peroxidase (VP), produced by the white-rot fungus Pleurotus eryngii, was investigated. VP can oxidize a wide variety of phenols, including hydroquinones, either directly in a manner similar to horseradish peroxidase (HRP), or indirectly through Mn3+ formed from Mn2+ oxidation, in a manner similar to manganese peroxidase (MnP). From several possible buffers (all pH 5), tartrate buffer was selected to study the oxidation of hydroquinones as it did not support the Mn2+-mediated activity of VP in the absence of exogenous H2O2 (unlike glyoxylate and oxalate buffers). In the absence of Mn2+, efficient hydroquinone oxidation by VP was dependent on exogenous H2O2. Under these conditions, semiquinone radicals produced by VP autoxidized to a certain extent producing superoxide anion radical (O2*-) that spontaneously dismutated to H2O2 and O2. The use of this peroxide by VP produced quinone in an amount greater than equimolar to the initial H2O2 (a quinone/H2O2 molar ratio of 1 was only observed under anaerobic conditions). In the presence of Mn2+, exogenous H2O2 was not required for complete oxidation of hydroquinone by VP. Reaction blanks lacking VP revealed H2O2 production due to a slow conversion of hydroquinone into semiquinone radicals (probably via autooxidation catalysed by trace amounts of free metal ions), followed by O2*- production through semiquinone autooxidation and O2*- reduction by Mn2+. This peroxide was used by VP to oxidize hydroquinone that was mainly carried out through Mn2+ oxidation. By comparing the activity of VP to that of MnP and HRP, it was found that the ability of VP and MnP to oxidize Mn2+ greatly increased hydroquinone oxidation efficiency.
Gómez-Toribio
V
V
Centro de Investigaciones Biológicas, CSIC, Madrid, Spain.
Martínez
A T
AT
Martínez
M J
MJ
Guillén
F
F
D006861:Hydrogen Peroxide / Q000378:metabolism*; D006873:Hydroquinones / Q000378:metabolism*; D008345:Manganese / Q000378:metabolism*; D010084:Oxidation-Reduction; D010544:Peroxidases / Q000378:metabolism*; D020076:Pleurotus / Q000201:enzymology*
D006873:Hydroquinones; D008345:Manganese; D006861:Hydrogen Peroxide; D010544:Peroxidases; C042858:lignin peroxidase; C051129:manganese peroxidase