Which enzyme is crucial for breaking down hydrogen peroxide in aerobic bacteria?
Aerobic respiration inevitably leaks electrons to dioxygen generating superoxide and hydrogen peroxide. H2O2 is particularly hazardous because ferrous iron drives Fenton reaction producing hydroxyl radical that nicks DNA phosphodiester backbone, carbonylates proteins, and peroxidizes lipids. Aerobes counter with catalase, extraordinarily efficient heme tetramer with kcat approaching ten million per second, diffusion limited perfect enzyme. Active site ferriprotoporphyrin IX cycles between ferric resting state and Compound I oxoferryl radical after binding first H2O2, then reduced by second H2O2 releasing water and dioxygen net reaction 2 H2O2 to 2 H2O plus O2 without external reductant. Escherichia coli encodes KatG bifunctional hydroperoxidase I during logarithmic growth and KatE HPII induced by RpoS sigma in stationary phase. Staphylococcus aureus catalase positivity yields vigorous bubbling, diagnostic distinction from Streptococcus. Deletion mutants exhibit hypersensitivity to H2O2, defective colonization, and increased mutation rates, underscoring central role in oxidative stress defense and survival in oxic niches and host tissues.
Ref: Madigan et al., Brock Biology of Microorganisms, 16th ed., Chapter 6: Oxidative stress - Catalase mechanism.