Faculty Collaboration Database

Mechanistic similarities between oxidation of hydroethidine by Fremy's salt and superoxide: stopped-flow optical and EPR studies. Free Radic Biol Med 2005 Oct 01;39(7):853-63

Date

09/06/2005

Pubmed ID

16140206

DOI

10.1016/j.freeradbiomed.2005.05.001

Scopus ID

2-s2.0-33644628456 (requires institutional sign-in at Scopus site)   88 Citations

Abstract

We have previously shown that superoxide radical anion (O2.-) reacts with hydroethidine (HE) to form a product that is distinctly different from ethidium (E+) (Zhao et al., Free Radic. Biol. Med. 34:1359; 2003). The structure of this product was recently determined as the 2-hydroxyethidium cation (2-OH-E+) (Zhao et al., Proc. Natl. Acad. Sci. USA 102:5727; 2005). In this study, using HPLC and mass spectrometry techniques, we show that 2-OH-E+ is formed from the reaction between HE and nitrosodisulfonate radical dianion (NDS) or Fremy's salt. The reaction kinetics and mechanism were determined using steady-state and time-resolved optical and EPR techniques. Within the first 50 ms, an intermediate was detected. Another intermediate absorbing strongly at 460 nm and weakly at 670 nm was detected within a second. The structure of this species was assigned to an imino quinone derivative of HE. The stoichiometry of the reaction indicates that two molecules of NDS were needed to oxidize a molecule of HE. We postulate that the first step of the reaction involves the hydrogen atom abstraction from HE to form an aminyl radical that reacts with another molecule of NDS to form an adduct that decomposes to an imino quinone derivative of HE. A similar mechanism has been proposed for the reaction between HE and O2.-. The reaction between HE and the Fremy's salt should provide a facile route for the synthesis of 2-OH-E+, a diagnostic marker product of the HE/O2.- reaction.

Author List

Zielonka J, Zhao H, Xu Y, Kalyanaraman B

Authors

Balaraman Kalyanaraman PhD Professor in the Biophysics department at Medical College of Wisconsin
Jacek M. Zielonka PhD Assistant Professor in the Biophysics department at Medical College of Wisconsin

MESH terms used to index this publication - Major topics in bold

Chromatography, High Pressure Liquid
Deuterium
Electron Spin Resonance Spectroscopy
Ethidium
Kinetics
Mass Spectrometry
Models, Chemical
Nitroso Compounds
Oxidation-Reduction
Oxygen Isotopes
Phenanthridines
Spectrometry, Fluorescence
Superoxides