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Title: Characterization of the Particulate Methane Monooxygenase Metal Centers in Multiple Redox States by X-ray Absorption Spectroscopy

Abstract

The integral membrane enzyme particulate methane monooxygenase (pMMO) converts methane, the most inert hydrocarbon, to methanol under ambient conditions. The 2.8-{angstrom} resolution pMMO crystal structure revealed three metal sites: a mononuclear copper center, a dinuclear copper center, and a nonphysiological mononuclear zinc center. Although not found in the crystal structure, solution samples of pMMO also contain iron. We have used X-ray absorption spectroscopy to analyze the oxidation states and coordination environments of the pMMO metal centers in as-isolated (pMMO{sub iso}), chemically reduced (pMMO{sub red}), and chemically oxidized (pMMO{sub ox}) samples. X-ray absorption near-edge spectra (XANES) indicate that pMMO{sub iso} contains both Cu{sup I} and Cu{sup II} and that the pMMO Cu centers can undergo redox chemistry. Extended X-ray absorption fine structure (EXAFS) analysis reveals a Cu-Cu interaction in all redox forms of the enzyme. The Cu-Cu distance increases from 2.51 to 2.65 {angstrom} upon reduction, concomitant with an increase in the average Cu-O/N bond lengths. Appropriate Cu2 model complexes were used to refine and validate the EXAFS fitting protocols for pMMO{sub iso}. Analysis of Fe EXAFS data combined with electron paramagnetic resonance (EPR) spectra indicates that Fe, present as Fe{sup III}, is consistent with heme impurities. These findings are complementarymore » to the crystallographic data and provide new insight into the oxidation states and possible electronic structures of the pMMO Cu ions.« less

Authors:
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
929827
Report Number(s):
BNL-80384-2008-JA
Journal ID: ISSN 0020-1669; INOCAJ; TRN: US200822%%1034
DOE Contract Number:  
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: Inorganic Chemistry; Journal Volume: 45
Country of Publication:
United States
Language:
English
Subject:
03 NATURAL GAS; 36 MATERIALS SCIENCE; ABSORPTION; ABSORPTION SPECTROSCOPY; BOND LENGTHS; CRYSTAL STRUCTURE; ELECTRON SPIN RESONANCE; ELECTRONIC STRUCTURE; FINE STRUCTURE; METALS; METHANE; PARTICULATES; national synchrotron light source

Citation Formats

Lieberman,R. Characterization of the Particulate Methane Monooxygenase Metal Centers in Multiple Redox States by X-ray Absorption Spectroscopy. United States: N. p., 2006. Web. doi:10.1021/ic060739v.
Lieberman,R. Characterization of the Particulate Methane Monooxygenase Metal Centers in Multiple Redox States by X-ray Absorption Spectroscopy. United States. doi:10.1021/ic060739v.
Lieberman,R. Sun . "Characterization of the Particulate Methane Monooxygenase Metal Centers in Multiple Redox States by X-ray Absorption Spectroscopy". United States. doi:10.1021/ic060739v.
@article{osti_929827,
title = {Characterization of the Particulate Methane Monooxygenase Metal Centers in Multiple Redox States by X-ray Absorption Spectroscopy},
author = {Lieberman,R.},
abstractNote = {The integral membrane enzyme particulate methane monooxygenase (pMMO) converts methane, the most inert hydrocarbon, to methanol under ambient conditions. The 2.8-{angstrom} resolution pMMO crystal structure revealed three metal sites: a mononuclear copper center, a dinuclear copper center, and a nonphysiological mononuclear zinc center. Although not found in the crystal structure, solution samples of pMMO also contain iron. We have used X-ray absorption spectroscopy to analyze the oxidation states and coordination environments of the pMMO metal centers in as-isolated (pMMO{sub iso}), chemically reduced (pMMO{sub red}), and chemically oxidized (pMMO{sub ox}) samples. X-ray absorption near-edge spectra (XANES) indicate that pMMO{sub iso} contains both Cu{sup I} and Cu{sup II} and that the pMMO Cu centers can undergo redox chemistry. Extended X-ray absorption fine structure (EXAFS) analysis reveals a Cu-Cu interaction in all redox forms of the enzyme. The Cu-Cu distance increases from 2.51 to 2.65 {angstrom} upon reduction, concomitant with an increase in the average Cu-O/N bond lengths. Appropriate Cu2 model complexes were used to refine and validate the EXAFS fitting protocols for pMMO{sub iso}. Analysis of Fe EXAFS data combined with electron paramagnetic resonance (EPR) spectra indicates that Fe, present as Fe{sup III}, is consistent with heme impurities. These findings are complementary to the crystallographic data and provide new insight into the oxidation states and possible electronic structures of the pMMO Cu ions.},
doi = {10.1021/ic060739v},
journal = {Inorganic Chemistry},
number = ,
volume = 45,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}