Nature of the intermediate formed in the reduction of O(2) to H(2)O at the trinuclear copper cluster active site in native laccase.
The multicopper oxidases contain at least four copper atoms and catalyze the four-electron reduction of O(2) to H(2)O at a trinuclear copper cluster. An intermediate, termed native intermediate, has been trapped by a rapid freeze-quench technique from Rhus vernicifera laccase when the fully reduced form reacts with dioxygen. This intermediate had been described as an oxygen-radical bound to the trinuclear copper cluster with one Cu site reduced. XAS, however, shows that all copper atoms are oxidized in this intermediate. A combination of EXAFS, multifrequency EPR, and VTVH MCD has been used to understand how this fully oxidized trinuclear Cu cluster relates to the fully oxidized resting form of the enzyme. It is determined that in the native intermediate all copper atoms of the cluster are bridged by the product of full O(2) reduction. In contrast, the resting form has one copper atom of the cluster (the T2 Cu) magnetically isolated from the others. The native intermediate decays to the resting oxidized form with a rate that is too slow to be in the catalytic cycle. Thus, the native intermediate appears to be the catalytically relevant fully oxidized form of the enzyme, and its role in catalysis is considered.
Lee
Sang-Kyu
SK
Department of Chemistry, Stanford University, Stanford, California 94305, USA.
George
Serena DeBeer
SD
Antholine
William E
WE
Hedman
Britt
B
Hodgson
Keith O
KO
Solomon
Edward I
EI
D001665:Binding Sites; D003300:Copper / Q000737:chemistry* / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D042845:Laccase; D008956:Models, Chemical; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism; D010100:Oxygen / Q000737:chemistry* / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism; D029045:Rhus / Q000201:enzymology; D013052:Spectrometry, X-Ray Emission; D013056:Spectrophotometry, Ultraviolet; D014867:Water / Q000737:chemistry* / Q000378:metabolism
D010940:Plant Proteins; D014867:Water; D003300:Copper; D010088:Oxidoreductases; D042845:Laccase; D010100:Oxygen