IMPORTANCE OF SE-GLUTATHIONE PEROXIDASE, CATALASE, AND CU ZN-SOD FOR CELL-SURVIVAL AGAINST OXIDATIVE STRESS/

Eukaryotic cells have to constantly cope with highly reactive oxygen-d erived free radicals. Their defense against these free radicals is ach ieved by natural antioxidant molecules but also by antioxidant enzymes . In this paper, we review some of the data comparing the efficiency o f three different antioxidant enzymes: Cu/Zn-superoxide dismutase (Cu/ Zn-SOD), catalase, and selenium-glutathione peroxidase. We perform our comparison on one experimental model (human fibroblasts) where the ac tivities of these three antioxidant enzymes have been modulated inside the cells, and the repercussion of these changes was investigated in different conditions. We also focus our attention on the protecting ro le of selenium-glutathione peroxidase, because this enzyme is very rar ely studied due to the difficulties linked to its biochemical properti es. These studies evidenced that all three antioxidant enzymes give pr otection for the cells. They show a high efficiency for selenium-gluta thione peroxidase and emphasize the fact that each enzyme has a specif ic as well as an irreplaceable function. They are all necessary for th e survival of the cell even in normal conditions. In addition, these t hree enzymes act in a cooperative or synergistic way to ensure a globa l cell protection. However, optimal protection is achieved only when a n appropriate balance between the activities of these enzymes is maint ained. Interpretation of the deleterious effects of free radicals has to be analyzed not only as a function of the amount of free radicals p roduced but also relative to the efficiency and to the activities of t hese enzymatic and chemical antioxidant systems. The threshold of prot ection can indeed vary dramatically as a function of the level of acti vity of these enzymes.