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Closed Access item Kinetic and chemical characterization of aldehyde oxidation by fungal aryl-alcohol oxidase

Authors:Ferreira, Patricia
Hernández-Ortega, Aitor
Herguedas, Beatriz
Rencoret, Jorge
Gutiérrez Suárez, Ana
Martínez, María Jesús
Jiménez-Barbero, Jesús
Medina, Milagros
Martínez Ferrer, Ángel Tomás
Keywords:aromatic aldehyde, aryl-alcohol oxidase (AAO), enzyme kinetics, gem-diol, GC-MS, 1H-NMR
Issue Date:2010
Publisher:Portland Press
Citation:Biochemical Journal 425: 585-593(2010)
Abstract:Fungal AAO (aryl-alcohol oxidase) provides H2O2 for lignin biodegradation. AAO is active on benzyl alcohols that are oxidized to aldehydes. However, during oxidation of some alcohols, AAO forms more than a stoichiometric number of H2O2 molecules with respect to the amount of aldehyde detected due to a double reaction that involves aryl-aldehyde oxidase activity. The latter reaction was investigated using different benzylic aldehydes, whose oxidation to acids was demonstrated by GC-MS. The steady- and presteady state kinetic constants, together with the chromatographic results, revealed that the presence of substrate electron-withdrawing or electron-donating substituents had a strong influence on activity; the highest activity was with p-nitrobenzaldehyde and halogenated aldehydes and the lowest with methoxylated aldehydes. Moreover, activity was correlated to the aldehyde hydration rates estimated by 1H-NMR. These findings, together with the absence in the AAO active site of a residue able to drive oxidation via an aldehyde thiohemiacetal, suggested that oxidation mainly proceeds via the gem-diol species. The reaction mechanism (with a solvent isotope effect, 2H2Okred, of approx. 1.5) would be analogous to that described for alcohols, the reductive half-reaction involving concerted hydride transfer from the α-carbon and proton abstraction from one of the gem-diol hydroxy groups by a base. The existence of two steps of opposite polar requirements (hydration and hydride transfer) explains some aspects of aldehyde oxidation by AAO. Site-directed mutagenesis identified two histidine residues strongly involved in gem-diol oxidation and, unexpectedly, suggested that an active-site tyrosine residue could facilitate the oxidation of some aldehydes that show no detectable hydration. Double alcohol and aldehyde oxidase activities of AAO would contribute to H2O2 supply by the enzyme
Description:9 páginas, 6 figuras, 3 tablas -- PAGS nros. 585-593
Publisher version (URL):http:// dx.doi.org/10.1042/BJ20091499
URI:http://hdl.handle.net/10261/48598
ISSN:0264-6021
E-ISSNmetadata.dc.identifier.doi = DOI:1470-8728
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