title: EPR stopped-flow studies of the reaction of the tyrosyl radical of protein R2 from ribonucleotide reductase with hydroxyurea.
abstract: The reaction of the functional tyrosyl radical in protein R2 of ribonucleotide reductase from E. coli and mouse with the enzyme inhibitor hydroxyurea has been studied by EPR stopped-flow techniques at room temperature. The rate of disappearance of the tyrosyl radical in E. coli protein R2 is k2 = 0.43 M-1 s-1 at 25 degrees C. The reaction follows pseudo-first-order kinetics up to 450 mM hydroxyurea indicating that no saturation by hydroxyurea takes place even at this high concentration. Transient nitroxide-like radicals from hydroxyurea have been detected for the first time in the reaction of hydroxyurea with protein R2 from E. coli and mouse, indicating that 1-electron transfer from hydroxyurea to the tyrosyl radical is the dominating mechanism in the inhibitor reaction. The hydroxyurea radicals appear in low steady-state concentrations during 2-3 half-decay times of the tyrosyl radical and disappear thereafter.
authors.affiliation: Max-Delbrück-Center of Molecular Medicine, Berlin, Germany.
authors.forename: G
authors.initials: G
authors.lastname: Lassmann
authors.forename: L
authors.initials: L
authors.lastname: Thelander
authors.forename: A
authors.initials: A
authors.lastname: Gräslund
mesh_terms: D000818:Animals; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D004926:Escherichia coli / Q000201:enzymology; D005609:Free Radicals; D006918:Hydroxyurea / Q000378:metabolism* / Q000494:pharmacology; D007700:Kinetics; D046911:Macromolecular Substances; D051379:Mice; D010084:Oxidation-Reduction; D012264:Ribonucleotide Reductases / Q000378:metabolism*
chemical_list: D005609:Free Radicals; D046911:Macromolecular Substances; D012264:Ribonucleotide Reductases; D006918:Hydroxyurea