Interaction of Peroxynitrite and Hydrogen Peroxide with Dinitrosyl Iron Complexes Containing Thiol Ligands in vitro

I. I. Lobysheva^*, V. A. Serezhenkov, and A. F. Vanin

Institute of Chemical Physics, Russian Academy of Sciences, ul. Kosygina 4, Moscow, 117977 Russia; fax: (095) 938-2156; E-mail: irlobysh@polymer.chph.ras.ru

^* To whom correspondence should be addressed.

Received July 21, 1998; Revision received September 21, 1998

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The interaction of peroxynitrite with thiolate dinitrosyl iron complexes (DNIC) has been examined and compared with the interaction with H₂O₂. Peroxynitrite oxidized DNIC containing various thiolate ligands--cysteine, glutathione, and bovine serum albumin. Analysis of the oxidation suggested a two-electron reaction and gave third-order rate constants of (9.3 ± 0.5)·10⁹ M^-2·sec^-1 for DNIC with BSA, (4.0 ± 0.3)·10⁸ M^-2·sec^-1 for DNIC with cysteine, and (1.8 ± 0.3)·10⁷ M^-2·sec^-1 for DNIC with glutathione at 20°C and pH 7.6. Peroxynitrite was more reactive towards DNIC than towards sulfhydryls. Addition of sodium dithionite after the reaction led to significant restoration of the EPR signal of DNIC with cysteine. The reaction of glutathione DNIC with H₂O₂ was about 600 times slower than with ONOO^- and not reversed by sodium dithionite. Thus peroxynitrite, in contrast to hydrogen peroxide, changes the pool of nitrosocompounds which can be responsible for interconversion, storage, and transportation of nitric oxide in vivo.

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KEY WORDS: nitric oxide, peroxynitrite, hydrogen peroxide, EPR spectroscopy of iron complexes, thiol oxidation, redox properties of nitrosyl adducts

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