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标题：A catalytic di-heme bis-Fe(IV) intermediate, alternative to an Fe(IV)=O porphyrin radical
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作者：Xianghui Li ; Rong Fu ; Sheeyong Lee 等
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2008
卷号：105
期号：25
页码：8597-8600
DOI：10.1073/pnas.0801643105
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：High-valent iron species are powerful oxidizing agents in chemical and biological catalysis. The best characterized form of an Fe(V) equivalent described in biological systems is the combination of a b-type heme with Fe(IV)=O and a porphyrin or amino acid cation radical (termed Compound I). This work describes an alternative natural mechanism to store two oxidizing equivalents above the ferric state for biological oxidation reactions. MauG is an enzyme that utilizes two covalently bound c-type hemes to catalyze the biosynthesis of the protein-derived cofactor tryptophan tryptophylquinone. Its natural substrate is a monohydroxylated tryptophan residue present in a 119-kDa precursor protein. An EPR-silent di-heme reaction intermediate of MauG was trapped. Mossbauer spectroscopy revealed the presence of two distinct Fe(IV) species. One is consistent with an Fe(IV)=O (ferryl) species ({delta} = 0.06 mm/s, {Delta}EQ = 1.70 mm/s). The other is assigned to an Fe(IV) heme species with two axial ligands from protein ({delta} = 0.17 mm/s, {Delta}EQ = 2.54 mm/s), which has never before been described in nature. This bis-Fe(IV) intermediate is remarkably stable but readily reacts with its native substrate. These findings broaden our views of how proteins can stabilize a highly reactive oxidizing species and the scope of enzyme-catalyzed posttranslational modifications.
关键词：ferryl ; posttranslational modification ; spectroscopy ; tryptophan tryptophylquinone (TTQ) ; free radical