Skip to content
Login Register

#bacterial enzyme

3 public questions tagged with this topic.

Microbial Physiology

Which bacterial enzyme neutralizes hydrogen peroxide?

Reactive oxygen species detoxification crucial for aerobic life. Hydrogen peroxide generated by flavoprotein oxidases and superoxide dismutase dismutation attacks iron sulfur clusters and via Fenton produces hydroxyl radical damaging DNA. Catalase provides efficient removal without reducing equivalents, dismutating two H2O2 to two water and one O2 through heme mediated cycle. Enzyme architecture tetrameric each subunit 60 kDa heme b, NADPH bound protecting against inactivation. Reaction proceeds two steps: oxidation of ferric heme to Compound I oxyferryl porphyrin cation radical by first H2O2, reduction back by second H2O2. High kcat near diffusion limit ensures low steady H2O2 nanomolar. Bacterial catalases KatG also possesses peroxidase activity active against organic hydroperoxides. Peroxidase distinct uses reductant NADH, AhpC uses thioredoxin. Superoxide dismutase produces H2O2 upstream. DNA gyrase unrelated. Catalase presence assay adding H2O2 to colonies releasing O2 bubbles differentiates catalase positive staphylococci and bacillus from catalase negative streptococci lactobacilli important for clinical diagnostics and understanding oxidative stress resistance in host tissues.

Ref: Madigan et al., Brock Biology of Microorganisms, Chapter 6: Catalase neutralizes H2O2.

View Details
Microbial Physiology

Which enzyme neutralizes hydrogen peroxide (H₂O₂) in bacterial cells?

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.

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 12: Catalase and Hydrogen Peroxide Detoxification.

View Details
Microbial Physiology

Which bacterial enzyme is involved in hydrolyzing organic phosphate esters during phosphate starvation?

Phosphate is often limiting nutrient in natural environments such as soils, freshwater lakes and host tissues, triggering broad starvation response orchestrated by Pho regulon controlled by two-component sensor kinase response regulator PhoR-PhoB. Under phosphate starvation where intracellular orthophosphate falls below micromolar threshold, bacteria induce high-affinity scavenging enzymes to liberate inorganic phosphate from organic sources. Alkaline phosphatase encoded by phoA in Escherichia coli is a periplasmic nonspecific phosphomonoesterase that hydrolyzes phosphoester bonds in diverse substrates including nucleotides like AMP, sugar phosphates, phospholipids and other organic phosphate compounds, releasing inorganic phosphate Pi for import via Pst high-affinity ABC transporter and low-affinity Pit system. The enzyme is a homodimer requiring two Zn2+ ions and one Mg2+ for catalysis, exhibiting high activity at alkaline pH 8 to 9 and serving as classic reporter of phosphate limitation. Its expression is tightly repressed when phosphate is abundant via PhoR-mediated phosphorylation state of PhoB. Superoxide dismutase detoxifies superoxide radical, DNA gyrase introduces negative supercoils into DNA, peptidyl transferase catalyzes peptide bond formation during translation, none participate in phosphate liberation, making alkaline phosphatase the definitive phosphate-starvation scavenger enzyme crucial for nutrient recycling and survival.

Ref: Madigan et al., Brock Biology of Microorganisms, 16th ed., Chapter 7: Pho Regulon and Alkaline Phosphatase Function.

View Details