Enzyme that protects the brain from free radical injury is -

Ans. is 'b' i.e., Superoxide dismutase Antioxidant mechanisms Cells have multiple mechanisms to remove free radicals and there by minimize injury. There are several nonenzymatic and enzymatic systems that contribute to inactivation of free radical reactions. A. Non-enzymatic system o Antioxidants (Vit 'E', Vit A, Vit C, glutathione and Cysteine) block the initiation of free radical formation and inactivate free radicals. o Tissue proteins (transferrin, ferritin, lactoferrin, and ceruloplasmin). As already explained, iron and copper can catalyze the formation of free radicals, these transpo and storage proteins decrease the reactive free iron and copper, thereby minimizing the free radical formation. B. Enzymatic system o A series of enzymes acts as free radical-scavenging systems and breakdown hydrogen peroxide and superoxide anion. 1. Catalase o Present in peroxisomes and decomposes H202 2 H202__________ 02 + 2 H20 2. Superoxide desmutase (SOD) o Manganese - superoxide dismutase is present in mitochondria, while copper-zinc-superoxide dismutase is found in the cytosol. o It conves superoxide to H202 2 02- + 2 H SOD 2 H202+ 02 3. Glutathione peroxidase o Present in mitochondria & cytosol. o It catalyzes free radical breakdown. H202+2 G S H __ GSSG+2H20 20H+ 2 G SH _ > GSSG+2H20 o Intracellular ratio of oxidized glutathione (G S S G) to reduced glutathione (G S M) is a reflection of the oxidative state of the cell.