Substances that suppress antioxidant enzyme (SOD, CAT,etc) activity induce oxidative stress. Under what conditions do substances that increase the activities of these enzyme induce stress? A situation where a substance X may increase SOD and CAT activities and yet deplete GSH and increase TBARS concentrations.
Cu,ZnSOD catalyses autoxidation of thiols (JBC 2002,277,1906–1911). This feature of the enzyme could be the reason why significant up regulation of CuZnSOD could be detrimental (Cu,Zn-Superoxide Dismutase Gene Dosage and Cell Resistance to Oxidative Stress: A Review. Bioscience Reports 1997; 17(1):85-89.)
After a stimuli from a substance, the cell responds by increasing the activity of antioxidant enzymes. The latter is the first step of response. If the effect of the substance is strong, (high concentration, long time of exposure) the antioxidant response is defeated by the oxidants, that leads to stress. condition.
A disturbance in prooxidant/antioxidant systems results oxidative stress which may directly induce or repress the protein that participate in these systems and deplete cellular stores of antioxidant materials such as glutathion, vitamin E and other antioxidant molecules.
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