Interaction of peroxynitrite and hydrogen peroxide with dinitrosyl iron complexes containing thiol ligands in vitro

The interaction of peroxynitrite with thiolate dinitrosyl iron complexes (D NIC) has been examined and compared with the interaction with H2O2. Peroxyn itrite oxidized DNIC containing various thiolate ligands-cysteine, glutathi one, and bovine serum albumin. Analysis of the oxidation suggested a two-el ectron reaction and gave third-order rate constants of (9.3 +/- 0.5).10(9) M-2.sec(-1) for DNIC with BSA, (4.0 +/- 0.3).10(8) M-2.sec(-1) for DNIC wit h cysteine, and (1.8 +/- 0.3) 10(7) M-2.sec(-1) for DNIC with glutathione a t 20 degrees C and pH 7.6. Peroxynitrite was more reactive towards DNIC tha n towards sulfhydryls. Addition of sodium dithionite after the reaction led to significant restoration of the EPR signal of DNIC with cysteine. The re action of glutathione DNIC with H2O2 was about 600 times slower than with O NOO- and not reversed by sodium dithionite. Thus peroxynitrite, in contrast to hydrogen peroxide, changes the pool of nitrosocompounds which can be re sponsible for interconversion, storage, and transportation of nitric oxide ill vivo.