katG encodes the bifunctional catalase-peroxidase (EC 1.11.1.21) of Pseudomonas putida KT2440, a soluble heme b-dependent hydroperoxidase. At a single heme active site it catalyzes two coupled reactions that detoxify hydrogen peroxide: a catalatic reaction dismutating H2O2 to water and oxygen (2 H2O2 -> O2 + 2 H2O), and a broad-spectrum peroxidatic reaction that reduces H2O2 to water using diverse organic electron donors (H2O2 + AH2 -> A + 2 H2O). The enzyme assembles as a homodimer or homotetramer and carries a covalent Trp-Tyr-Met crosslink that is required for the catalase but not the peroxidase activity. As a major H2O2-scavenging enzyme, KatG is a central component of the bacterial defense against oxidative stress.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004096 catalase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Catalase activity is one of the two core molecular functions of this bifunctional enzyme. UniProt records the catalatic reaction (2 H2O2 = O2 + 2 H2O) under EC 1.11.1.21 and the FUNCTION line explicitly describes catalase activity. Reason: The catalatic dismutation of hydrogen peroxide is a defining, well-supported core activity for a catalase-peroxidase and matches the UniProt catalytic-activity reaction and EC assignment. Supporting Evidence: file:PSEPK/katG/katG-uniprot.txt Reaction=2 H2O2 = O2 + 2 H2O file:PSEPK/katG/katG-uniprot.txt Bifunctional enzyme with both catalase and broad-spectrum file:PSEPK/katG/katG-uniprot.txt PTHR30555; HYDROPEROXIDASE I, BIFUNCTIONAL CATALASE-PEROXIDASE |
| GO:0004601 peroxidase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Peroxidase activity is the second core molecular function of this bifunctional enzyme. UniProt records the peroxidatic reaction (H2O2 + AH2 = A + 2 H2O) and describes broad-spectrum peroxidase activity. Reason: The broad-spectrum peroxidatic reduction of H2O2 using organic electron donors is a defining core activity of catalase-peroxidases and is directly supported by the UniProt catalytic-activity reaction. Supporting Evidence: file:PSEPK/katG/katG-uniprot.txt Reaction=H2O2 + AH2 = A + 2 H2O file:PSEPK/katG/katG-uniprot.txt Bifunctional enzyme with both catalase and broad-spectrum |
| GO:0005829 cytosol | IEA GO_REF:0000118 | KEEP AS NON CORE | Summary: Cytosolic localization is a reasonable TreeGrafter prediction for a soluble bacterial catalase-peroxidase, but it is an IEA inference with no KT2440-specific localization evidence and is peripheral to the gene's core function. Reason: Catalase-peroxidases are typically soluble cytoplasmic enzymes, so the prediction is biologically plausible, but the annotation is electronic only and the cellular location is not the core defining feature of the gene. Supporting Evidence: file:PSEPK/katG/katG-uniprot.txt Homodimer or homotetramer. |
| GO:0006979 response to oxidative stress | IEA GO_REF:0000002 | ACCEPT | Summary: Response to oxidative stress is a core biological process for KatG: by scavenging hydrogen peroxide it directly protects the cell against oxidative damage. Reason: H2O2 decomposition by catalase-peroxidase is a principal mechanism of defense against oxidative stress, consistent with the bifunctional H2O2-detoxifying activity recorded in UniProt. Supporting Evidence: file:PSEPK/katG/katG-uniprot.txt Bifunctional enzyme with both catalase and broad-spectrum file:PSEPK/katG/katG-notes.md central component of the cellular defense against oxidative/H2O2 stress. |
| GO:0020037 heme binding | IEA GO_REF:0000120 | MARK AS OVER ANNOTATED | Summary: Heme b binding is mechanistically essential for this enzyme (UniProt records heme b as cofactor and an axial heme-iron binding residue), but as a cofactor-binding term it is broad relative to the specific catalase and peroxidase activity terms already present. Reason: The annotation is correct and the heme is required for catalysis, but with the specific catalase and peroxidase molecular-function terms present, the generic heme-binding term adds little to the functional description and represents the cofactor-binding aspect rather than the core activity. Supporting Evidence: file:PSEPK/katG/katG-uniprot.txt Name=heme b; Xref=ChEBI:CHEBI:60344 file:PSEPK/katG/katG-uniprot.txt Binds 1 heme b (iron(II)-protoporphyrin IX) group per dimer. |
| GO:0042744 hydrogen peroxide catabolic process | IEA GO_REF:0000118 | ACCEPT | Summary: Hydrogen peroxide catabolic process is the core biological process directly effected by both the catalase and peroxidase activities of KatG, which consume H2O2. Reason: Both UniProt catalytic-activity reactions consume hydrogen peroxide, making H2O2 catabolism the most direct process-level description of this enzyme's role. Supporting Evidence: file:PSEPK/katG/katG-uniprot.txt Reaction=2 H2O2 = O2 + 2 H2O file:PSEPK/katG/katG-uniprot.txt Reaction=H2O2 + AH2 = A + 2 H2O |
| GO:0070301 cellular response to hydrogen peroxide | IEA GO_REF:0000118 | KEEP AS NON CORE | Summary: Cellular response to hydrogen peroxide is consistent with KatG's role in decomposing H2O2 as part of the cell's defensive reaction to peroxide exposure; it is a valid but somewhat more peripheral process term than the direct H2O2 catabolic process. Reason: The annotation is biologically reasonable for an H2O2-scavenging enzyme, but the direct H2O2 catabolic process term more precisely captures the enzyme's core contribution; this response term is retained as non-core. Supporting Evidence: file:PSEPK/katG/katG-uniprot.txt Bifunctional enzyme with both catalase and broad-spectrum |
| GO:0098869 cellular oxidant detoxification | IEA GO_REF:0000120 | KEEP AS NON CORE | Summary: Cellular oxidant detoxification is correctly inferred from the catalase and peroxidase activities (the GOA entry derives it from GO:0004096 and GO:0004601), capturing the protective antioxidant role of KatG. Reason: The term accurately describes the detoxification outcome of H2O2 decomposition but is more general than the specific hydrogen peroxide catabolic process term; it is retained as a valid non-core process annotation. Supporting Evidence: file:PSEPK/katG/katG-uniprot.txt Bifunctional enzyme with both catalase and broad-spectrum file:PSEPK/katG/katG-notes.md central component of the cellular defense against oxidative/H2O2 stress. |
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Download this section (compressed HTML)Q: Is katG expression in Pseudomonas putida KT2440 induced by hydrogen peroxide or governed by an OxyR-type regulator, and how does it partition with other catalases in H2O2 defense?
Suggested experts: Bacterial oxidative-stress regulation specialists, Pseudomonas physiologists
Q: What is the relative in vivo contribution of the catalatic versus peroxidatic activity of KatG to H2O2 detoxification under different growth and stress conditions?
Suggested experts: Enzyme mechanism researchers, Redox biochemists
Experiment: Delete katG (PP_3668) in KT2440, optionally in combination with other catalase genes, and measure H2O2 sensitivity, residual catalase/peroxidase activity, and survival under oxidative stress.
Type: Gene knockout and phenotyping
Experiment: Purify recombinant KatG and confirm heme b incorporation, catalase and peroxidase activities, and the dependence of catalatic (but not peroxidatic) activity on the Trp-Tyr-Met crosslink via site-directed mutagenesis.
Type: Enzyme assay and cofactor analysis
Experiment: Fractionate KT2440 to verify the predicted cytosolic localization of KatG and rule out periplasmic or membrane association.
Type: Subcellular fractionation
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