NaMPO1_candidate_AMO_3 is the best current NICAT mapping for the classical MPO1 step that oxidizes N-methylputrescine toward the N-methyl-Delta1-pyrrolinium branch intermediate. UniProt already assigns the exact N-methylputrescine oxidase reaction and nicotine-pathway placement to this peroxisomal copper amine oxidase, making it a strong upstream pathway anchor rather than a loose family candidate.
Definition: Catalysis of the oxidation of N-methylputrescine to 4-methylaminobutanal, hydrogen peroxide, and ammonium during nicotine biosynthesis.
Justification: The available GO terms capture only broader primary amine or diamine oxidase chemistry, whereas the nicotine pathway uses a specific N-methylputrescine oxidase step.
Parent term: primary methylamine oxidase activity
Supporting Evidence:
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005507 copper ion binding | IEA GO_REF:0000120 | ACCEPT | Summary: Copper binding is an appropriate cofactor annotation for this amine oxidase. Reason: Copper is explicitly curated as a cofactor for this topaquinone-dependent oxidase family. |
| GO:0005777 peroxisome | IEA GO_REF:0000120 | KEEP AS NON CORE | Summary: Peroxisomal localization is plausible and worth retaining as non-core context. Reason: UniProt places this candidate in the peroxisome, but the main review conclusion is the catalytic pathway role. Supporting Evidence: file:NICAT/NaMPO1_candidate_AMO_3/NaMPO1_candidate_AMO_3-uniprot.txt CC -!- SUBCELLULAR LOCATION: Peroxisome |
| GO:0008131 primary methylamine oxidase activity | IEA GO_REF:0000120 | ACCEPT | Summary: This is the best current GO molecular-function term for MPO1 chemistry. Reason: UniProt assigns the exact oxidation of N-methylputrescine to this copper amine oxidase. Supporting Evidence: file:NICAT/NaMPO1_candidate_AMO_3/NaMPO1_candidate_AMO_3-notes.md UniProt curates A0A314KPU1 as AMO_3, assigns the exact oxidation of N-methylputrescine to 4-methylaminobutanal, places the protein in nicotine biosynthesis, and localizes it to the peroxisome. |
| GO:0009308 amine metabolic process | IEA GO_REF:0000120 | MARK AS OVER ANNOTATED | Summary: This process annotation is true but too broad to be the main curation outcome. Reason: The informative biology here is the specific MPO1 step in nicotine biosynthesis rather than generic amine metabolism. |
| GO:0048038 quinone binding | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: Quinone binding is an appropriate cofactor-level annotation for this enzyme family. Reason: Topaquinone chemistry is relevant to catalytic mechanism, but it is a secondary conclusion relative to the pathway reaction itself. |
| GO:0052597 diamine oxidase activity | IEA GO_REF:0000117 | MODIFY | Summary: This broader amine-oxidase term should be collapsed to the more specific primary methylamine oxidase annotation. Reason: GO:0008131 more closely matches the curated MPO1 reaction and avoids keeping two near-duplicate family-level activity labels. Proposed replacements: primary methylamine oxidase activity |
| GO:0042179 nicotine biosynthetic process | TAS file:NICAT/NaMPO1_candidate_AMO_3/NaMPO1_candidate_AMO_3-notes.md | NEW | Summary: MPO1 belongs in the core nicotine biosynthetic process. Reason: MPO is part of the minimal upstream module that generates the N-methylpyrrolinium branch intermediate feeding the completed pathway. Supporting Evidence: file:NICAT/NaMPO1_candidate_AMO_3/NaMPO1_candidate_AMO_3-notes.md The glucosylation preprint keeps MPO in the minimal upstream nicotine module by using ODC, PMT, and MPO to generate N-methylpyrrolinium, and it places MPO1 among the genes most correlated with A622. |
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Download this section (compressed HTML)Q: Does A0A314KPU1 account for most MPO flux in Nicotiana attenuata roots, or are additional amine oxidase paralogs partially redundant?
Q: Is the attenuata MPO1 candidate substrate-selective for N-methylputrescine relative to broader diamine substrates in vivo?
Experiment: Compare A0A314KPU1 with related amine oxidase paralogs in recombinant assays using N-methylputrescine and alternative diamines.
Hypothesis: A0A314KPU1 is the principal N-methylputrescine oxidase in the nicotine pathway.
Type: biochemical substrate-specificity assay
Experiment: Knock out the primary MPO1 candidate in roots and measure N-methylputrescine, 4-methylaminobutanal-derived intermediates, and nicotine accumulation.
Hypothesis: Loss of the AMO_3 candidate will reduce upstream pyrrolinium-branch flux into nicotine.
Type: genetic perturbation plus metabolite profiling
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