title: Tryptophan and tyrosine radicals in ribonucleotide reductase: a comparative high-field EPR study at 94 GHz.
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.
authors.affiliation: Max-Volmer-Laboratorium für Biophysikalische Chemie, Institut für Chemie, Technische Universität Berlin, PC 14, Strasse des 17. Juni 135, D-10623 Berlin, Germany.
authors.forename: G
authors.initials: G
authors.lastname: Bleifuss
authors.forename: M
authors.initials: M
authors.lastname: Kolberg
authors.forename: S
authors.initials: S
authors.lastname: Pötsch
authors.forename: W
authors.initials: W
authors.lastname: Hofbauer
authors.forename: R
authors.initials: R
authors.lastname: Bittl
authors.forename: W
authors.initials: W
authors.lastname: Lubitz
authors.forename: A
authors.initials: A
authors.lastname: Gräslund
authors.forename: G
authors.initials: G
authors.lastname: Lassmann
authors.forename: F
authors.initials: F
authors.lastname: Lendzian
mesh_terms: D000818:Animals; D004578:Electron Spin Resonance Spectroscopy; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D005609:Free Radicals / Q000737:chemistry; D051379:Mice; D016297:Mutagenesis, Site-Directed; D021122:Protein Subunits; D012264:Ribonucleotide Reductases / Q000737:chemistry* / Q000235:genetics; D014364:Tryptophan / Q000737:chemistry; D014443:Tyrosine / Q000737:chemistry
chemical_list: D005609:Free Radicals; D021122:Protein Subunits; D014443:Tyrosine; D014364:Tryptophan; D012264:Ribonucleotide Reductases