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Cytochrome P450-catalyzed dealkylation of atrazine by Rhodococcus sp. strain NI86/21 involves hydrogen atom transfer rather than single electron transfer
(Royal Society of Chemistry, 2014) Meyer, Armin H.; Dybała-Defratyka, Agnieszka; Alaimo, Peter J.; Geronimo, Inacrist; Sanchez, Ariana D.; Cramer, Christopher J.; Elsner, Martin
Cytochrome P450 enzymes are responsible for a multitude of natural transformation reactions. For oxidative N-dealkylation, single electron (SET) and hydrogen atom abstraction (HAT) have been debated as underlying mechanisms. Combined evidence from (i) product distribution and (ii) isotope effects indicate that HAT, rather than SET, initiates N-dealkylation of atrazine to desethyl- and desisopropylatrazine by the microorganism Rhodococcus sp. strain NI86/21. (i) Product analysis revealed a non-selective oxidation at both the αC and βC-atom of the alkyl chain, which is expected for a radical reaction, but not SET. (ii) Normal 13C and 15N as well as pronounced 2H isotope effects (εcarbon: −4.0‰ ± 0.2‰; εnitrogen: −1.4‰ ± 0.3‰, KIEH: 3.6 ± 0.8) agree qualitatively with calculated values for HAT, whereas inverse 13C and 15N isotope effects are predicted for SET. Analogous results are observed with the Fe(IV)[double bond, length as m-dash]O model system [5,10,15,20-tetrakis(pentafluorophenyl)porphyrin-iron(III)-chloride + NaIO4], but not with permanganate. These results emphasize the relevance of the HAT mechanism for N-dealkylation by P450.
A DFT and ONIOM study of C–H hydroxylation catalyzed by nitrobenzene 1,2-dioxygenase
(Royal Society of Chemistry, 2014) Geronimo, Inacrist; Paneth, Piotr
A detailed description of the mechanism of C–H hydroxylation by Rieske non-heme iron dioxygenases remains elusive, as the nature of the oxidizing species is not definitively known. DFT calculations on cluster models of nitrobenzene 1,2-dioxygenase were done to explore possible mechanisms arising from oxidation by either the experimentally observed FeIII–OOH complex or the putative high-valent HO–FeVQO intermediate formed through a heterolytic O–O bond cleavage. Hydrogen abstraction by HO–FeVQO, followed by oxygen rebound, was found to be consistent with experimental studies. The findings from the quantum mechanical cluster approach were verified by accounting for the effect of the protein environment on transition state geometries and reaction barriers through ONIOM calculations.