Why Does the Active Form of Galactose Oxidase Possess a Diamagnetic Ground State?

Müller, Jochen; Weyhermüller, Thomas; Bill, Eckhard; Hildebrandt, Peter; Ould-Moussa, Linda; Glaser, Thorsten; Wieghardt, Karl

doi:10.1002/(sici)1521-3773(19980316)37:5<616::aid-anie616>3.0.co;2-4

Cited by 100 publications

(7 citation statements)

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“…GO oxy is EPR silent due to antiferromagnetic coupling of the phenoxyl radical to the copper(II) center (1,9,27). In smallmolecule Cu II -phenoxyl radical complexes, the difference between antiferromagnetic and ferromagnetic coupling arises from differences in the angular overlap of the unpaired spin containing orbitals (27,12,20,24,(36)(37)(38).…”

Section: ½1mentioning

confidence: 99%

“…In smallmolecule Cu II -phenoxyl radical complexes, the difference between antiferromagnetic and ferromagnetic coupling arises from differences in the angular overlap of the unpaired spin containing orbitals (27,12,20,24,(36)(37)(38). The orientation of the aromatic ring relative to the Cu coordination basal plane observed in crystal structures of Cu(II)-salen complexes precludes the orbital overlap required for antiferromagnetic coupling (13,16).…”

Section: ½1mentioning

confidence: 99%

“…The X-band EPR spectra of ½1 SR2 þ contain broad features near the g ¼ 2 region similar to a Cu II center and do not contain half-field signals (Δm s ¼ 2), which would be characteristic of a triplet species (27).…”

Section: ½1mentioning

confidence: 99%

“…EPR characterization of the sulfur contribution to the hole stabilization is not feasible for GO oxy as antiferromagnetic coupling (J > 200 cm −1 ) between the Cu II center and the tyrosyl radical leads to a diamagnetic ground state (9,27). We have evaluated sulfur K-edge X-ray absorption spectroscopy (XAS) as a complimentary technique for experimental quantification of the sulfur contribution in complexes with complicated or silent EPR spectra such as ½1 SR2 þ and GO oxy .…”

mentioning

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: ½1mentioning

confidence: 99%

Section: ½1mentioning

confidence: 99%

Section: ½1mentioning

confidence: 99%

mentioning

confidence: 99%

See 2 more Smart Citations

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 Cu(II)-phenoxyl radical complex, on the other hand, has two electron spins on different nuclei, and therefore the spin-spin interaction should be considered in [29][30][31]. In the case of the oxidized Cu(II) salen-type complexes, since correlation between ligand p-orbital and the copper dx2-y2 orbital having an unpaired electron is close to orthogonal, the d-electron spin of copper ion coupled with radical electron spin ferromagnetically [60]. mB.M.…”

Section: Magnetic Properties Of One-electron Oxidized Metal Salen-typmentioning

confidence: 99%

Oxidation Chemistry of Metal(II) Salen-Type Complexes

Shimazaki¹

2013

Electrochemistry

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Vom Strukturmodell der Galactose-Oxidase zur homogenen Katalyse: effiziente aerobe Oxidation von Alkoholen

et al. 1998

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Zwei Reaktionswege katalysiert der zweikernige Kupfer(II)‐Phenoxyl‐Komplex 1 – ein funktionelles Modell des Metalloenzyms Galactose‐Oxidase – bei der Oxidation von primären und sekundären Alkoholen mit Sauerstoff (Luft) in homogener Lösung. Dabei entstehen die entsprechenden Aldehyde bzw. Ketone und/oder 1,2‐Glycole (oxidative C‐C‐Kupplung); als Reduktionsprodukt entsteht nicht Wasser, sondern H2O2.

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Why Does the Active Form of Galactose Oxidase Possess a Diamagnetic Ground State?

Cited by 100 publications

References 2 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

Oxidation Chemistry of Metal(II) Salen-Type Complexes

Vom Strukturmodell der Galactose-Oxidase zur homogenen Katalyse: effiziente aerobe Oxidation von Alkoholen

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