Rapid-freeze-quench magnetic circular dichroism of intermediate X in ribonucleotide reductase: New structural insight

Nataša Mitić, Lana Saleh, Gerhard Schenk, J. Martin Bollinger, Edward I. Solomon

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Abstract

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: 16000-22000 cm-1 region involving spin-allowed ligand field transitions of the Fe(IV), 23000-24000 cm-1 region of spin-forbidden, spin-flip transitions on the Fe(IV), and the charge transfer (CT) region from 26000 to 32000 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-μ-oxo and μ-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.

Original languageEnglish (US)
Pages (from-to)11200-11201
Number of pages2
JournalJournal of the American Chemical Society
Volume125
Issue number37
DOIs
Publication statusPublished - Sep 17 2003

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All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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