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  • Title: Tryptophan and tyrosine radicals in ribonucleotide reductase: a comparative high-field EPR study at 94 GHz.
    Author: Bleifuss G, Kolberg M, Pötsch S, Hofbauer W, Bittl R, Lubitz W, Gräslund A, Lassmann G, Lendzian F.
    Journal: Biochemistry; 2001 Dec 18; 40(50):15362-8. PubMed ID: 11735419.
    Abstract:
    Tryptophan radicals, which are generated in the reconstitution reaction of mutants Y122F and Y177W of subunit R2 apoprotein of E. coli and mouse ribonucleotide reductase (RNR), respectively, with Fe(2+) and oxygen, are investigated by high-field EPR at 94 GHz and compared with the tyrosine radicals occurring in the respective wild-type proteins. For the first time, accurate g-values are obtained for protein-associated neutral tryptophan free radicals, which show only a small anisotropy. The apparent hyperfine patterns observed in frozen solutions are very similar for tryptophan and tyrosine radicals in mouse subunit R2 at conventional X-band EPR. The radicals can, however, be discriminated by their different g-tensors using high-field EPR. Tryptophan radicals were postulated as reaction intermediates in the proposed radical transfer pathway of RNR. Furthermore, the data obtained here for the electronic structure of protein-associated tryptophan neutral free radicals are important for identification and understanding of the functional important tryptophan radicals which occur in other enzymes, e.g., DNA photolyase and cytochrome c peroxidase, where they are magnetically coupled to other radicals or to a metal center.
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