CAT and major depressive disorder: Researchers had shown that oxidative stress plays an important role in depression.[74] Major antioxidative defenses include both enzymatic and nonenzymatic antioxidants.[74] The enzymatic antioxidants levels, such as catalase, superoxide dismutase, and glutathione peroxidase, were modified in depressive patients.[75] The levels of nonenzymatic antioxidants were also altered in depressive patients.