Electron paramagnetic resonance investigations of a kinetically competent intermediate formed in ribonucleotide reduction: Evidence for a thiyl radical-cob(II)alamin interaction

G. J. Gerfen, S. Licht, J. P. Willems, B. M. Hoffman, J. Stubbe

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Abstract

The ribonucleoside triphosphate reductase (RTPR) from Lactobacillus leichmannii requires adenosylcobalamin (AdoCbl) as a cofactor to catalyze the conversion of nucleotides to deoxynucleotides. RTPR has previously been shown to catalyze the homolytic cleavage of the carbon-cobalt bond of AdoCbl, and the resulting paramagnetic species has been characterized by rapid freeze-quench EPR spectroscopy (Orme-Johnson, W.H.; Beinert, H.; Blakley, R.L., J. Biol. Chem. 1974, 249, 2338-2343. Licht, S.; Gerfen, O.J.; Stubbe, J. Science 1996, 271, 477-481). This study presents simulations of X- and Q-band EPR spectra of this intermediate. Modeling this species as a thiyl radical coupled to cob(II)alamin by electron-electron exchange and dipolar interactions yields reasonable fits to spectra obtained at both microwave frequencies, whereas simulations that employ a single-spin model do not. This modeling provides support for the intermediacy of a thiyl radical in this system. The techniques employed here may prove generally useful in simulation of similar spectra observed in other B12-dependent enzyme systems.

Original languageEnglish (US)
Pages (from-to)8192-8197
Number of pages6
JournalJournal of the American Chemical Society
Volume118
Issue number35
DOIs
Publication statusPublished - Jan 1 1996
Externally publishedYes

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ASJC Scopus subject areas

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

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