Mitic, Natasa and Saleh, Lana and Schenk, Gerhard and Bollinger, J. Martin Jr. and Solomon, Edward I.
Rapid-Freeze-Quench Magnetic Circular Dichroism of Intermediate X in
Ribonucleotide Reductase: New Structural Insight.
Journal of the American Chemical Society, 125 (37).
To elucidate the electronic structure of intermediate X in the oxygen activation reaction of the R2 subunit of ribonucleotide reductase, a protocol has been developed to perform magnetic circular dichroism (MCD) on a rapid-freeze-quench, strain free optical sample. RFQ-MCD data have been collected on intermediate X in the double mutant of R2, Y122/Y356F. While X has been reported to exhibit a broad absorption band at 365 nm, there are at least 10 electronic transitions observed at low-temperature MCD. From C0/D0 ratios, the transitions of X can be divided into three regions: 16 000-22 000 cm-1 region involving spin-allowed ligand field transitions of the Fe(IV), 23 000-24 000 cm-1 region of spin-forbidden, spin-flip transitions on the Fe(IV), and the charge transfer (CT) region from 26 000 to 32 000 cm-1. The C0/D0 ratios from d --> d and CT transitions strongly support significant Fe(IV) character coupled into the paramagnetic center. Ligand field (spin-allowed d --> d region) analysis allows the bis-mu-oxo and mu-oxo plus other monoanionic bridge possibilities for the structure of intermediate X to be distinguished, providing new insight into the molecular mechanism of the cluster formation in R2.
||The definitive version of this article is available at the Journal of the American Chemical Society, 2003, v.125, pp.11200-11201 . © 2003 American Chemical Society
||Rapid-Freeze-Quench; Magnetic Circular Dichroism; Intermediate X; Ribonucleotide Reductase;
||Science & Engineering > Chemistry
||06 Jun 2012 14:24
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||Journal of the American Chemical Society
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