Active site models for galactose oxidase containing two different phenol groups

Masayasu Taki, Hideyuki Kumei, Shigenori Nagatomo, Teizo Kitagawa, Shinobu Itoh, Shunichi Fukuzumi

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Model complexes of the active site of galactose oxidase (GAO) have been developed using a new ligand carrying two different phenol groups, N-[(2-hydroxy-3-methylthio-5-tert-butylphenyl)methyl].N-[(2-hydroxy-3,5-di-te rt-butylphenyl)methyl].2-(2-pyridyl)ethylamine (L1H2). Deprotonated ligand L12- forms a dimeric Cu(II) complex, [Cu(II)2(L12-)2], in the solid state, the structure of which has been determined by X-ray crystallographic analysis. The dimeric Cu(II)-diphenolate complex can be converted into the monomeric complex, [Cu(II)(L12-)(X)] (X = py, AcO, and PhCH2OH), in solution by adding exogenous ligands such as pyridine (py), acetate (AcO-), or benzyl alcohol (PhCH2OH). The structure and physicochemical properties (UV-Vis, ESR, redox potential) of [Cu(II)(L12-)(X)] have been explored as a model for the resting state of the enzyme. One-electron oxidation of [Cu(II)(L12-)(py)] and [Zn(II)(L12-)(py)] by (NH4)2[Ce(IV)CNO3)6] (CAN) yielded the corresponding phenoxyl radical/phenolate complexes, Cu(II)(LI(·)-) and Zn(II)(L1(·)-), respectively, which have also been characterized by UV-Vis, resonance Raman, and ESR. The structure, physicochemical properties and reactivities of the diphenolate and phenoxyl radical/phenolate complexes of L1H2 are compared to those of the corresponding monophenolate and monophenoxyl radical complexes in order to obtain further insight into the role of Tyr 495 in the native enzyme. (C) 2000 Elsevier Science S.A.

Original languageEnglish
Pages (from-to)622-632
Number of pages11
JournalInorganica Chimica Acta
StatePublished - 30 Apr 2000

Bibliographical note

Funding Information:
The present study was financially supported in part by a Grant-in-Aid for Scientific Research on Priority Areas (Molecular Biometallics: 10129218 and 11116219; Electrochemistry of Ordered Interface: 10131242 and 11118244; Creation of Delocalized Conjugated Electronic System: 10146232) from the Ministry of Education, Science, Sports, and Culture of Japan and by Research Fellowships of the Japan Society for the Promotion of Science for Young Scientists (no. 02410). We also thank Professor Yasushi Kai and his co-workers, particularly, Ms Eiko Mochizuki of Osaka University, for their assistance in the X-ray measurements.


  • Cofactor
  • Copper complexes
  • Galactose oxidase
  • Phenoxyl radical
  • Zinc complexes


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