| Abstrakt: |
The free radical intermediates formed during the nitrosation of thiols including glutathione (GSH), L-cysteine (CystSH), captopril (CapSH) and N-acetylpenicillamine (NAPenSH) by NO&z.rad; at physiological pH have been investigated using EPR spectroscopy combined with the spin trap DMPO. We have found that NO&z.rad; in the presence of oxygen reacted with GSH, CystSH and CapSH to generate the corresponding thiyl radicals, which are spin trapped by DMPO to give the spin trapped adducts DMPO-SG, DMPO-SCyst and DMPO-SCap respectively. In the case of NAPenSH no spin trapped adduct is detected. Desferrioxamine, an inhibitor of peroxynitrite (ONOO–), has no effect on the formation of either DMPO-SG or DMPO-SCyst, suggesting that ONOO– is not involved in the formation of GS&z.rad; and Cyst&z.rad;. In contrast, desferrioxamine inhibits the detection of DMPO-SCap, pointing to a role for ONOO– in the formation of CapS&z.rad;. Our results demonstrate that &z.rad;NO2 is the most likely reactive species in the nitrosation of GSH and CystSH by oxygenated NO&z.rad;, thereby generating the corresponding thiyl radicals. Furthermore, our data indicate that the scavenging of NO&z.rad; by thiols may lead to the production of superoxide (O2&z.rad;–) via the formation of thiyl radicals. |
