%0 Journal Article
%A Roncal, Tomás
%A Muñoz, Carmen
%A Lorenzo, Leire
%A Maestro, Belén
%A Díaz de Guereñu, María del Mar
%T Two-step oxidation of glycerol to glyceric acid catalyzed by the Phanerochaete chrysosporium glyoxal oxidase
%D 2012
%@ 0141-0229
%U https://hdl.handle.net/11556/4286
%X Glyoxal oxidase of P. chrysosporium is a radical copper oxidase that catalyzes oxidation of aldehydes to carboxylic acids coupled to dioxygen reduction to H 2O 2. In addition to known substrates, glycerol is also found to be a substrate for glyoxal oxidase. During enzyme turnover, glyoxal oxidase undergoes a reversible inactivation, probably caused by loss of the active site free radical, resulting in short-lasting enzyme activities and undetectable substrate conversions. Enzyme activity could be extended by including two additional enzymes, horseradish peroxidase and catalase, in addition to a redox chemical activator, such as Mn(III) (or Mn(II)+H 2O 2) or hexachloroiridate. Using this three-enzyme system glycerol was converted in glyceric acid in a two-step reaction, with glyceraldehyde as intermediate. A possible operation mechanism is proposed in which the three enzymes would work coordinately allowing to maintain a sustained glyoxal oxidase activity. In the course of its catalytic cycle, glyoxal oxidase alternates between two functional and interconvertible reduced and oxidized forms resulting from a two-electron transfer process. However, glyoxal oxidase can also undergo an one-electron reduction to a catalytically inactive form lacking the active site free radical. Horseradish peroxidase could use glyoxal oxidase-generated H 2O 2 to oxidize Mn(II) to Mn(III) which, in turn, would reoxidize and reactivate the inactive form of glyoxal oxidase. Catalase would remove the excess of H 2O 2 generated during the reaction. In spite of the improvement achieved using the three-enzyme system, glyoxal oxidase inactivation still occurred, which resulted in low substrate conversions. Possible causes of inactivation, including end-product inhibition, are discussed.
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