Spectroscopic and electronic structure studies of intermediate X in ribonucleotide reductase R2 and two variants: A description of the Fe IV-oxo bond in the FeIII-O-FeIV dimer

Mitic N., Clay M.D., Saleh L., Bollinger Jr. J.M. and Solomon E.I. (2007) Spectroscopic and electronic structure studies of intermediate X in ribonucleotide reductase R2 and two variants: A description of the Fe IV-oxo bond in the FeIII-O-FeIV dimer. Journal of the American Chemical Society, 129 29: 9049-9065. doi:10.1021/ja070909i


Author Mitic N.
Clay M.D.
Saleh L.
Bollinger Jr. J.M.
Solomon E.I.
Title Spectroscopic and electronic structure studies of intermediate X in ribonucleotide reductase R2 and two variants: A description of the Fe IV-oxo bond in the FeIII-O-FeIV dimer
Journal name Journal of the American Chemical Society   Check publisher's open access policy
ISSN 0002-7863
Publication date 2007-07-25
Sub-type Article (original research)
DOI 10.1021/ja070909i
Volume 129
Issue 29
Start page 9049
End page 9065
Total pages 17
Subject 1600 Chemistry
Abstract Spectroscopic and electronic structure studies of the class I Escherichia coli ribonucleotide reductase (RNR) intermediate X and three computationally derived model complexes are presented, compared, and evaluated to determine the electronic and geometric structure of the FeIII-FeIV active site of intermediate X. Rapid freeze-quench (RFQ) EPR, absorption, and MCD were used to trap intermediate X in R2 wild-type (WT) and two variants, W48A and Y122F/Y356F. RFQ-EPR spin quantitation was used to determine the relative contributions of intermediate X and radicals present, while RFQ-MCD was used to specifically probe the FeIII/FeIV active site, which displayed three FeIV d-d transitions between 16 700 and 22 600 cm-1, two FeIV d-d spin-flip transitions between 23 500 and 24 300 cm-1, and five oxo to FeIV and FeIII charge transfer (CT) transitions between 25 000 and 32 000 cm-1. The FeIV d-d transitions were perturbed in the two variants, confirming that all three d-d transitions derive from the d-π manifold. Furthermore, the FeIV d-π splittings in the WT are too large to correlate with a bis-μ-oxo structure. The assignment of the FeIV d-d transitions in WT intermediate X best correlates with a bridged μ-oxo/μ-hydroxo [Fe III(μ-O)(μ-OH)FeIV] structure. The μ-oxo/μ-hydroxo core structure provides an important σ/π superexchange pathway, which is not present in the bis-μ-oxo structure, to promote facile electron transfer from Y122 to the remote FeIV through the bent oxo bridge, thereby generating the tyrosyl radical for catalysis.
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Unknown

Document type: Journal Article
Sub-type: Article (original research)
Collection: Scopus Import
 
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Created: Tue, 26 Nov 2013, 19:28:07 EST by System User