Practice question

Hydrogen peroxide at even low micromolar concentrations of 1 to 2 micromolar causes inactivation of mononuclear iron enzymes and iron-sulfur dehydratases such as fumarase via Fenton chemistry generating highly reactive hydroxyl radicals that oxidize DNA generating 8-oxoguanine and protein carbonyls leading to mutagenesis. Bacteria deploy specialized scavenging enzymes for peroxide detoxification. Catalases are predominantly heme-containing tetrameric enzymes containing protoheme IX or heme b in each active site that dismutate two molecules of H2O2 into water and molecular oxygen with extremely high turnover numbers approaching diffusion-limited rates around 10^6 to 10^7 per second and Michaelis constants in millimolar range. Monofunctional catalases KatG possessing catalase-peroxidase bifunctionality and KatE plus manganese catalases are induced by OxyR, PerR and during stationary phase under general stress sigma factor RpoS. Catalase activity is readily assayed macroscopically by vigorous bubble formation when colony is exposed to 3 percent peroxide solution. DNA helicase unwinds DNA duplex for replication, RNA polymerase alpha-beta complex transcribes genes to mRNA, duplication in provided options likely reflects typographic error, but catalytic degradation of peroxide remains exclusive biochemical function of catalase, often operating redundantly with alkyl hydroperoxide reductase AhpCF and glutathione peroxidases in multilayer antioxidant defense protecting genome integrity.