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Composition and Structure of the Inorganic Core of Relaxed Intermediate X(Y122F) of Escherichia coli Ribonucleotide Reductase.
- Source :
-
Journal of the American Chemical Society . 12/16/2015, Vol. 137 Issue 49, p15558-15566. 9p. - Publication Year :
- 2015
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Abstract
- Activation of the diferrous center of the ß2 (R2) subunit of the class 1a Escherichia coli ribonucleotide reductases by reaction with O2 followed by one-electron reduction yields a spin-coupled, paramagnetic Fe(III)/Fe(IV) intermediate, denoted X, whose identity has been sought by multiple investigators for over a quarter of a century. To determine the composition and structure of X, the present study has applied 57Fe, 14,15N, 17O, and ¹H electron nuclear double resonance (ENDOR) measurements combined with quantitative measurements of 17O and ¹H electron paramagnetic resonance line-broadening studies to wild-type X, which is very short-lived, and to X prepared with the Y122F mutant, which has a lifetime of many seconds. Previous studies have established that over several seconds the as-formed X(Y122F) relaxes to an equilibrium structure. The present study focuses on the relaxed structure. It establishes that the inorganic core of relaxed X has the composition [(OH-)FeIII-O-FeIV]: there is no second inorganic oxygenic bridge, neither oxo nor hydroxo. Geometric analysis of the 14N ENDOR data, together with recent extended X-ray absorption fine structure measurements of the Fe-Fe distance (Dassama, L. M.; et al. J. Am. Chem. Soc. 2013, 135, 16758), supports the view that X contains a "diamond-core" Fe(III)/Fe(IV) center, with the irons bridged by two ligands. One bridging ligand is the oxo bridge (OBr) derived from O2 gas. Given the absence of a second inorganic oxygenic bridge, the second bridging ligand must be protein derived, and is most plausibly assigned as a carboxyl oxygen from E238. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 00027863
- Volume :
- 137
- Issue :
- 49
- Database :
- Academic Search Index
- Journal :
- Journal of the American Chemical Society
- Publication Type :
- Academic Journal
- Accession number :
- 112020668
- Full Text :
- https://doi.org/10.1021/jacs.5b10763