Catechol Oxidase

Eicken, Christoph; Gerdemann, Carsten; Krebs, Bernt

doi:10.1002/0470028637.met196

Cited by 6 publications

(7 citation statements)

References 65 publications

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“…Hemocyanin and catechol oxidase also belong to this class. Tyrosinase catalyzes two different reactions, [1][2][3][4][5] the oxidation of phenol (tyrosine) to ortho-quinone, and the conversion of ortho-diphenol to ortho-quinone, both with the help of dioxygen. Hemocyanin is an oxygen transport protein without phenolase or diphenolase activity, and catechol oxidase has only diphenolase activity.…”

Section: Introductionmentioning

confidence: 99%

Comparison of QM-only and QM/MM models for the mechanism of tyrosinase

Siegbahn

Borowski

2011

Faraday Discuss.

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Two previous studies on the mechanism of tyrosinase have given quite conflicting results. In a QM-only study using a rather small model, a mechanism was suggested in which the tyrosine proton is removed before catalysis. This was followed by catalytic cycles where a superoxo ligand attacks the phenolate ring. In another, more recent study, at the QM/MM level including the entire protein in the model, a quite different mechanism was instead advocated where a bridging O2H ligand was homolytically cleaved. That mechanism was rejected in the earlier QM-only study as having a prohibitively large barrier for O-O bond cleavage. In the present study, this discrepancy between the previous studies is investigated by new QM-only and QM/MM calculations.

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Section: Introductionmentioning

confidence: 99%

Comparison of QM-only and QM/MM models for the mechanism of tyrosinase

Siegbahn

Borowski

2011

Faraday Discuss.

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“…[4] Two-electron oxidation of o-diphenols (catechols) to o-quinones is also catalyzed by the related enzyme catechol oxidase (CO), which, however, lacks monooxygenase activity. [5,6] The active sites of Ty and CO exhibit two copper atoms both of which are coordinated by three histidine residues (type 3 copper). The third group of proteins with type 3 copper active sites is that of hemocyanins (Hc), which serve as oxygen carriers in some arthropods and mollusks and exhibit highly cooperative oxygenbinding characteristics.…”

Section: Introductionmentioning

confidence: 99%

Aromatic Hydroxylation in a Copper Bis(imine) Complex Mediated by a μ‐η²:η² Peroxo Dicopper Core: A Mechanistic Scenario

Sander

Henß

Näther

et al. 2008

Chemistry A European J

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Detailed mechanistic studies on the ligand hydroxylation reaction mediated by a copper bis(imine) complex are presented. Starting from a structural analysis of the CuI complex and the CuII product with a hydroxylated ligand, the optical absorption and vibrational spectra of starting material and product are analyzed. Kinetic analysis of the ligand hydroxylation reaction shows that O2 binding is the rate-limiting step. The reaction proceeds much faster in methanol than in acetonitrile. Moreover, an inverse kinetic isotope effect (KIE) is evidenced for the reaction in acetonitrile, which is attributed to a sterically congested transition state leading to the peroxo adduct. In methanol, however, no KIE is observed. A DFT analysis of the oxygenation reaction mediated by the micro-eta2:eta2 peroxo core demonstrates that the major barrier after O2 binding corresponds to electrophilic attack on the arene ring. The relevant orbital interaction occurs between the sigma* orbital of the Cu2O2 unit and the HOMO of the ligand. On the basis of the activation energy for the rate-limiting step (18.3 kcal mol(-1)) this reaction is thermally allowed, in agreement with the experimental observation. The calculations also predict the presence of a stable dienone intermediate which, however, escaped experimental detection so far. Reasons for these findings are considered. The implications of the results for the mechanism of tyrosinase are discussed.

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“…Multinuclear Cu sites in metalloproteins are of key importance in a wide range of functions, including oxygen transport (hemocyanin), electron transfer (Cu A from cytochrome c oxidase [C c O] and nitrous oxide reductase [N 2 OR]), , oxidases and oxygenases (catechol oxidase, ascorbate oxidase, and particulate methane monooxygenase [pMMO], for example), , and the reduction of nitrous oxide to dinitrogen (Cu Z from N 2 OR) . Particularly, germane to the complexes reported herein are the binuclear mixed-valence Cu A center, the binuclear Cu center in pMMO, and the trinuclear centers of multicopper oxidases.…”

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confidence: 99%