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  • Title: Loss of the tyrosyl radical in mouse ribonucleotide reductase by (-)-epicatechin.
    Author: Schroeder P, Voevodskaya N, Klotz LO, Brenneisen P, Gräslund A, Sies H.
    Journal: Biochem Biophys Res Commun; 2005 Jan 21; 326(3):614-7. PubMed ID: 15596143.
    Abstract:
    The flavonoid (-)-epicatechin was previously demonstrated to interfere with tyrosine nitration by peroxynitrite [Biochem. Biophys. Res. Commun. 285 (2001) 782]. This effect was hypothesized to be based upon an interaction of epicatechin with a transiently generated tyrosyl radical. In the present study, using electron paramagnetic resonance, we demonstrate that (-)-epicatechin is capable of destabilizing the tyrosyl radical of the mouse ribonucleotide reductase R2 component. First-order rate constants for the disappearance of tyrosyl radical signals were 1 x 10(-4) and 2 x 10(-4)s(-1)for epicatechin and hydroxyurea, a well-known tyrosyl radical scavenger, respectively. In keeping with scavenging the ribonucleotide reductase tyrosyl radical, cellular production of deoxyribonucleotides and DNA synthesis were impaired by (-)-epicatechin in normal human keratinocytes and in human squamous carcinoma cells.
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