Analytical Sciences

Generation Mechanism of Deferoxamine Radical by Tyrosine-Tyrosinase Reaction

Mika TADA,* Yoshimi NIWANO,** and Masahiro KOHNO***

*Center for General Education, Tohoku Institute of Technology, 35-1 Yagiyama, Kasumicho, Taihaku, Sendai 982-8577, Japan
**Tohoku University Graduate School of Dentistry, 4-1 Seiryo-maich, Aoba, Sendai 980-8575, Japan
***Department of Bioengineering, Tokyo Institute of Technology, 4259-G1-25, Nagatsuta-cho, Midori, Yokohama 226-8502, Japan

Nitroxide radical formations of deferoxamine mesylate (DFX) that is used clinically to treat iron-overload patients was examined by a tyrosine-tyrosinase reaction system as models of the H-atom transfer or proton-coupled electron transfer. When DFX was exposed to the tyrosine-tyrosinase reaction, nine-line ESR spectrum (g = 2.0063, hfcc; aN = 0.78 mT, aH(2) = 0.63 mT) was detected, indicating that the oxidation of DFX leads to a nitroxide radical. The signal intensity of the DFX radical increased dependently on the concentrations of tyrosine and tyrosinase. The amounts of DMPO-OH spin adducts via the tyrosine-tyrosinase reaction declined with DFX. Furthermore, mass spectra of an extra removed from the tyrosine-tyrosinase reaction mixture showed that the enzyme reactions might not be degradations of DFX. Therefore, there might be two types of DFX reaction passways, which could be through an internal electron transfer from tyrosine and hydrogen absorptions by ·OH directly.

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