Galactose oxidase models: solution chemistry, and phenoxyl radical generation mediated by the copper status.
Galactose oxidase (GO) is an enzyme that catalyzes two-electron oxidations. Its active site contains a copper atom coordinated to a tyrosyl radical, the biogenesis of which requires copper and dioxygen. We have recently studied the properties of electrochemically generated mononuclear Cu(II)-phenoxyl radical systems as model compounds of GO. We present here the solution chemistry of these ligands under various copper and dioxygen statuses: N(3)O ligands first chelate Cu(II), leading, in the presence of base, to [Cu(II)(ligand)(CH(3)CN)](+) complexes (ortho-tert-butylated ligands) or [(Cu(II))(2)(ligand)(2)](2+) complexes (ortho-methoxylated ligands). Excess copper(II) then oxidizes the complex to the corresponding mononuclear Cu(II)-phenoxyl radical species. N(2)O(2) tripodal ligands, in the presence of copper(II), afford directly a copper(II)-phenoxyl radical species. Addition of more than two molar equivalents of copper(II) affords a Cu(II)-bis(phenoxyl) diradical species. The donor set of the ligand directs the reaction towards comproportionation for ligands possessing an N(3)O donor set, while disproportionation is observed for ligands possessing an N(2)O(2) donor set. These results are discussed in the light of recent results concerning the self-processing of GO. A path involving copper(II) disproportionation is proposed for oxidation of the cross-linked tyrosinate of GO, supporting the fact that both copper(I) and copper(II) activate the enzyme.
Michel
Fabien
F
Laboratoire de Chimie Biomimétique, LEDSS, UMR CNRS 5616, Université J. Fourier, BP 53, 38041 Grenoble Cedex 9, France.
Thomas
Fabrice
F
Hamman
Sylvain
S
Saint-Aman
Eric
E
Bucher
Christophe
C
Pierre
Jean-Louis
JL
D000097:Acetonitriles / Q000737:chemistry; D001665:Binding Sites; D003300:Copper / Q000737:chemistry*; D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals / Q000737:chemistry; D005692:Galactose Oxidase / Q000737:chemistry / Q000378:metabolism*; D007202:Indicators and Reagents; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D012996:Solutions; D013056:Spectrophotometry, Ultraviolet
D000097:Acetonitriles; D005609:Free Radicals; D007202:Indicators and Reagents; D008024:Ligands; D012996:Solutions; D003300:Copper; D005692:Galactose Oxidase