The authors have studied the susceptibility of two key protective enzymes, glutathione peroxidase (GPX) and glutathione reductase (GR) to the reactive oxygen species (ROS) known to induce oxidative damage in vitro system containing Fe2+/EDTA. The ability of ROS scavanger stobadine to prevent oxidative damage was also studied. Incubation of GPX with Fe2+/EDTA resulted in the significant decrease in its enzyme activity while under the same condition the activity of GR was not changed. The presence of stobadine was effective in protecting GPX from the loss of its activity by in vitro oxidizing agents. The monitoring of the mitochondrial outer membrane dynamics by the method of synchronous fluorescence fingerprint showed that the membrane is involved in these processes. (Fig. 3, Ref. 35.)