Zum Problem des Low-spin-Charakters von Cytochrom P450cam im „Resting State” – Untersuchungen von Enzymmodellen mit Puls-EPR- und ENDOR-Spektroskopie

Der Mechanismus der Alkanhydroxylierung [1] durch Cytochrom P450 wirft interessante Fragen auf. Nach dem allgemein akzeptierten Mechanismus [2] (Schema 1) erfolgt im Schema 1. Schematische Darstellung des Wiederanbindungs-Mechanismus.Schema 2. a) Orbitaldiagramme der Low-Spin-und High-Spin-Kopplung des Hydroxoeisen-Komplexes im Triplettzustand mit dem Alkylradikal im Wiederanbindungsschritt. b) Die Elektronenverschiebung beim Auffüllen des ¹Lochsª im a 2u -Orbital des Porphyrinrestes.

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The High-Valent Compound of Cytochrome P450: The Nature of the Fe−S Bond and the Role of the Thiolate Ligand as an Internal Electron Donor

Ogliaro

Cohen

Filatov

et al. 2000

Angewandte Chemie

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Recently, Schlichting et al. [1] have used time-lapse X-ray crystallography to ªphotographº the hydroxylation pathway of camphor by cytochrome P450 cam , which includes the elusive, high-valent iron-oxene species (1 in Scheme 1 a). In response to this exciting work, we present here an extensive density functional theoretical (DFT) investigation of iron ∆ Fe O CysS protoporphyrin IX 1.65 Å 2.3 ± 0.2 Å Fe O L porphyrin a) b) L = HS − , CH 3 S − , CysS − 1 L = HS -(2a), CH 3 S -(2b), CysS -(2c) Scheme 1. Selected X-ray diffraction data for a) the high-valent P450 iron oxene species 1. D indicates the protrusion of the iron center from the porphyrin plane. b) Model systems 2 a ± c.oxene (2 a ± c, Scheme 1 b) with emphasis on geometry, electronic structure, and unusual features of the FeÀS bonding. Thus, while the X-ray diffracting species [1] qualitatively fits iron oxene, its precise geometric data are less certain. For example, the distance between the iron and the proximal ligand, r Fe-S , appears quite short but the value 2.3 AE 0.2 has a significant uncertainty. Another uncertainty, discussed by the authors, [1] is the possible contamination by an additional species. Theory [2] itself has not as yet settled on a value for this distance, which appears to vary between 2.37 ± 2.69 for different models systems and computational levels. [2] An associated issue is the theoretical characterization of the flexibility of the Fe À S linkage in 1 and the role of the thiolate ligand as an internal electron donor. [3] A still uncertain feature of P450 iron oxene is whether it involves a porphyrin cation radical, as in the analogous Compound I species of horseradish peroxidase [4a] and synthetic models, [4b] or, rather, does it possess a sulfur radical situation, [2a,e] or perhaps a resonance hybrid of these forms. [3,5] A related question concerns the spin-state identity; high-spin as in some Compound I species, [4a,b] or low thermochemical energy scale. [15] The more reactive oxoiron porphyrin systems [16] are under current investigation.

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Zum Problem des Low-spin-Charakters von Cytochrom P450cam im „Resting State” – Untersuchungen von Enzymmodellen mit Puls-EPR- und ENDOR-Spektroskopie

Cited by 9 publications

References 24 publications

Über den „Neuanbindungs”-Mechanismus der Alkanhydroxylierung durch Cytochrom P450: elektronische Struktur der Zwischenstufe und Charakter des Elektronentransfers bei der Neuanbindung

Über den „Neuanbindungs”-Mechanismus der Alkanhydroxylierung durch Cytochrom P450: elektronische Struktur der Zwischenstufe und Charakter des Elektronentransfers bei der Neuanbindung

Zwei Reaktionswege beim „Wiederanbindungs”-Mechanismus der Alkanhydroxylierung durch Cytochrom P450: Entstehung freier Radikale mit begrenzter Lebensdauer

The High-Valent Compound of Cytochrome P450: The Nature of the Fe−S Bond and the Role of the Thiolate Ligand as an Internal Electron Donor

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