Phenoxyl-copper(II) complexes: models for the active site of galactose oxidase

Sokolowski, Achim; Leutbecher, Heiko; Weyhermüller, Thomas; Schnepf, Robert; Bothe, Eberhard; Bill, Eckhard; Hildebrandt, Peter; Wieghardt, Karl

doi:10.1007/s007750050155

Cited by 116 publications

(115 citation statements)

References 20 publications

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“…Discussion Models of GO generally use ortho-sulfanylphenols to provide faithful structural correspondence to the covalent bond between Cys228 and the ortho position of Tyr272 (12,(17)(18)(19)(20)(21)(22)(23)(24)(25)(26). The results herein show that para-sulfanyl substituents have electrochemical and spectroscopic effects comparable to those at ortho position, while allowing variation in the steric demands of the alkylsulfanyl group with minimal potential changes in the copper coordination geometry.…”

Section: Resultsmentioning

confidence: 61%

“…17;000 cm −1 features of ½1 SR2 þ nearly double in intensity. The features in ½1 SR2 þ can be assigned to intraring sulfur-aryl π → π Ã transitions (see below), though the energies and intensities are higher than those observed for ortho-alkylsulfanyl substituted phenoxyl radicals (18,20,26). The intensity of these features in ½1 SR þ and ½1 SR 2þ increases in the order −S t Bu > −S i Pr > −SMe, which correlates with increased delocalization of the hole on the sulfur atom with −SMe.…”

Section: Resultsmentioning

confidence: 94%

“…12,[17][18][19][20][21][22][23][24][25][26]. The para positioning of sulfanyl substituents in 1 R2 is designed purposefully to assure minimal copper coordination changes by preserving the sterically abutting ortho-t-butyl substituents (R 3 , Fig.…”

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confidence: 99%

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Sulfanyl stabilization of copper-bonded phenoxyls in model complexes and galactose oxidase

Verma

Pratt

Storr

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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Integrating sulfanyl substituents into copper-bonded phenoxyls significantly alters their optical and redox properties and provides insight into the influence of cysteine modification of the tyrosine cofactor in the enzyme galactose oxidase. The model complexes ½1 SR2 þ are class II mixed-valent Cu II -phenoxyl-phenolate species that exhibit intervalence charge transfer bands and intense visible sulfur-aryl π → π Ã transitions in the energy range, which provides a greater spectroscopic fidelity to oxidized galactose oxidase than non-sulfur-bearing analogs. The potentials for phenolate-based oxidations of the sulfanyl-substituted 1 SR2 are lower than the alkylsubstituted analogs by up to ca. 150 mV and decrease following the steric trend: −S t Bu > −S i Pr > −SMe. Density functional theory calculations suggest that reducing the steric demands of the sulfanyl substituent accommodates an in-plane conformation of the alkylsulfanyl group with the aromatic ring, which stabilizes the phenoxyl hole by ca. 8 kcal mol −1 (1 kcal ¼ 4.18 kJ; 350 mV) through delocalization onto the sulfur atom. Sulfur K-edge X-ray absorption spectroscopy clearly indicates a contribution of ca. 8-13% to the hole from the sulfur atoms in ½1 SR2 þ . The electrochemical results for the model complexes corroborate the ca. 350 mV (density functional theory) contribution of hole delocalization on to the cysteine-tyrosine cross-link to the stability of the phenoxyl radical in the enzyme, while highlighting the importance of the in-plane conformation observed in all crystal structures of the enzyme.Marcus-Hush analysis | density functional theory reduction potentials | noninnocent ligands | magnetic coupling G alactose oxidase (GO) is an enzyme that selectively oxidizes primary alcohols to aldehydes via a unique Cu II -tyrosyl radical with concomitant reduction of dioxygen to hydrogen peroxide (1, 2). The active site of GO contains a Cu center ligated by two histidines, one unmodified tyrosine (axial) and one tyrosine residue (equatorial) that is covalently cross-linked to a cysteine residue in a posttranslational oxidative modification step (3-5) (Fig. 1). The consensus mechanism involves two catalytically relevant forms: the reduced (GO red ), which contains a Cu I -tyrosine unit, and the oxidized (GO oxy ), which contains a Cu II center and a cysteine-modified tyrosyl radical. One-electron reduction of GO oxy generates the inactive semireduced (GO semi ) form, which contains a Cu II -tyrosinate unit. Cysteine-modification of the redox-active tyrosine significantly influences the redox properties of the active oxidant: The potential of the Tyr-Cys/Tyr•-Cys couple estimated from the GO semi ∕ GO oxy interconversion is ca. 400 mV [vs. normal hydrogen electrode (NHE), pH 7.5], which is significantly lower than free tyrosine in solution (ca. 900 mV) and unmodified redox-active tyrosines in other enzymes (ca. 660-1,000 mV) (1, 6). Delocalization of the tyrosyl radical onto the thioether bridge, which is predicted by density functional theory (DFT) compu...

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Section: Resultsmentioning

confidence: 61%

Section: Resultsmentioning

confidence: 94%

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Sulfanyl stabilization of copper-bonded phenoxyls in model complexes and galactose oxidase

Verma

Pratt

Storr

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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“…The general method used to prepare these complexes was to react a [M(β-diketonate) 3 , was prepared according to the general method employed for β-diketonate containing complexes but using manganese(III) acetate as a starting compound.…”

Section: Complex Synthesismentioning

confidence: 99%

“…Chelating ligands in which one or more of the "arms" consist of phenol groups have been used extensively for the preparation of copper complexes that model the active site of the enzyme galactose oxidase, [1][2][3][4][5] and also in the synthesis of iron and manganese complexes to model the active sites of various dioxygenase and phosphatase enzymes. [6][7][8][9][10][11] Lipoxygenases are nonheme, non-sulfur iron or manganese dioxygenases that act on lipid substrates containing one or more (Z,Z)-1,4-pentadiene moieties.…”

Section: Introductionmentioning

confidence: 99%

The Synthesis, Structures and Characterisation of New Mixed‐Ligand Manganese and Iron Complexes with Tripodal, Tetradentate Ligands

et al. 2008

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The preparation of new manganese and iron complexes with the general formula [M(tripod)(anion)] is described, where M = Fe III or Mn III , "tripod" is a dianionic tetradentate tripodal ligand and the anion is a chelating β-diketonate, 8-oxyquinoline or acetate. The synthesis of this type of complexes was found to be straightforward, which allows for the preparation of a large variety of such coordination compounds. The complexes are characterised by X-ray crystallography, infrared spectroscopy, UV/Vis spectroscopy, cyclic voltammetry and elemental analysis. A correlation between the ligand sets and the electron density at the metal centre in the complexes is

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Warum hat die aktive Form der Galactose-Oxidase einen diamagnetischen Grundzustand?

et al. 1998

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Phenoxyl-copper(II) complexes: models for the active site of galactose oxidase

Cited by 116 publications

References 20 publications

Sulfanyl stabilization of copper-bonded phenoxyls in model complexes and galactose oxidase

Sulfanyl stabilization of copper-bonded phenoxyls in model complexes and galactose oxidase

The Synthesis, Structures and Characterisation of New Mixed‐Ligand Manganese and Iron Complexes with Tripodal, Tetradentate Ligands

Warum hat die aktive Form der Galactose-Oxidase einen diamagnetischen Grundzustand?

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