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

详细信息    查看全文

• 作者：Raquel L. Lieberman ; Kalyan C. Kondapalli ; Deepak B. Shrestha ; Amanda S. Hakemian ; Stephen M. Smith ; Joshua Telser ; Jane Kuzelka ; Rajeev Gupta ; A. S. Borovik ; Stephen J. Lippard ; Brian M. Hoffman ; Amy
• 刊名：Inorganic Chemistry
• 出版年：2006
• 出版时间：October 2, 2006
• 年：2006
• 卷：45
• 期：20
• 页码：8372 - 8381
• 全文大小：306K
• 年卷期：v.45,no.20(October 2, 2006)
• ISSN：1520-510X

文摘

The integral membrane enzyme particulate methane monooxygenase (pMMO) converts methane, the most inerthydrocarbon, to methanol under ambient conditions. The 2.8-Å resolution pMMO crystal structure revealed threemetal sites: a mononuclear copper center, a dinuclear copper center, and a nonphysiological mononuclear zinccenter. Although not found in the crystal structure, solution samples of pMMO also contain iron. We have usedX-ray absorption spectroscopy to analyze the oxidation states and coordination environments of the pMMO metalcenters in as-isolated (pMMO_iso), chemically reduced (pMMO_red), and chemically oxidized (pMMO_ox) samples. X-rayabsorption near-edge spectra (XANES) indicate that pMMO_iso contains both Cu^I and Cu^II and that the pMMO Cucenters can undergo redox chemistry. Extended X-ray absorption fine structure (EXAFS) analysis reveals a Cu-Cuinteraction in all redox forms of the enzyme. The Cu-Cu distance increases from 2.51 to 2.65 Å upon reduction,concomitant with an increase in the average Cu-O/N bond lengths. Appropriate Cu₂ model complexes were usedto refine and validate the EXAFS fitting protocols for pMMO_iso. Analysis of Fe EXAFS data combined with electronparamagnetic resonance (EPR) spectra indicates that Fe, present as Fe^III, is consistent with heme impurities.These findings are complementary to the crystallographic data and provide new insight into the oxidation statesand possible electronic structures of the pMMO Cu ions.