Practice question

Superoxide radical generated when flavoenzymes and respiratory chain components univalently reduce oxygen, highly toxic inactivating dehydratases bearing exposed iron sulfur clusters like aconitase and fumarase releasing free iron that fuels Fenton chemistry producing hydroxyl radical. Superoxide dismutase constitutes primary defense dismutating two superoxides into dioxygen and hydrogen peroxide reaction two O2 superoxide plus two protons to O2 plus H2O2. Enzymes classified by metal cofactor manganese SodA inducible by SoxRS, iron SodB constitutive, copper zinc SodC periplasmic exported via Sec pathway. Periplasmic SodC crucial for pathogenic survival inside macrophages generating oxidative burst. Product H2O2 subsequently detoxified by catalase KatG KatE and alkyl hydroperoxide reductase AhpCF. Without SOD cells show auxotrophy for branched chain amino acids, elevated mutation frequency, and sensitivity to redox cycling agents paraquat. Therefore enzyme role is conversion of superoxide into oxygen and peroxide, not DNA repair nor ATP enhancement, intermediate step in reactive oxygen species detoxification cascade protecting metalloproteins and genome integrity during aerobic growth.