期刊
JOURNAL OF INORGANIC BIOCHEMISTRY
卷 100, 期 4, 页码 480-501出版社
ELSEVIER SCIENCE INC
DOI: 10.1016/j.jinorgbio.2006.01.008
关键词
horseradish peroxidase; chloroperoxidase; resonance Raman; oxoiron(IV); porphyrin pi-cation radical; heme proteins; iron-oxygen bonds
资金
- NIGMS NIH HHS [GM 57042] Funding Source: Medline
The catalytic cycle intermediates of heme peroxidases, known as compounds I and II, have been of long standing interest as models for intermediates of heme proteins, such as the terminal oxidases and cytochrome P450 enzymes, and for non-heme iron enzymes as well. Reports of resonance Raman signals for compound I intermediates of the oxo-iron(IV) porphyrin pi-cation radical type have been sometimes contradictory due to complications arising from photolability, causing compound I signals to appear similar to those of compound II or other forms. However, studies of synthetic systems indicated that protein based compound I intermediates of the oxoiron(IV) porphyrin pi-cation radical type should exhibit vibrational signatures that are different from the non-radical forms. The compound I intermediates of horseradish peroxidase (HRP), and chloroperoxidase (CPO) from Caldariomyces fumago do in fact exhibit unique and characteristic vibrational spectra. The nature of the putative oxoiron(IV) bond in peroxidase intermediates has been under discussion in the recent literature, with suggestions that the Fe-IV=O unit might be better described as Fe-IV OH. The generally low Fe-IV=O stretching frequencies observed for proteins have been difficult to mimic in synthetic ferryl porphyrins via electron donation from trans axial ligands alone. Resonance Raman studies of iron-oxygen vibrations within protein species that are sensitive to pH, deuteration, and solvent oxygen exchange, indicate that hydrogen bonding to the oxoiron(IV) group within the protein environment contributes to substantial lowering of Fe-IV=O frequencies relative to those of synthetic model compounds. (c) 2006 Elsevier Inc. All rights reserved.
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