nrfA encodes cytochrome c nitrite reductase, an ammonia-forming periplasmic multiheme enzyme of anaerobic respiratory nitrite reduction in Desulfotalea psychrophila. The protein reduces nitrite to ammonium using cytochrome c as electron donor; direct DP0344 biochemical and operon evidence remains sparse.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005509 calcium ion binding | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: KEEP_AS_NON_CORE. Calcium may be a family-level cofactor feature, but the core function is heme-dependent nitrite reduction. Reason: InterPro detects cytochrome c-552/nitrite reductase family features, and NrfA enzymes are multiheme cytochromes. Calcium binding may be associated with the fold, but the direct functional annotation should center on heme binding and ammonia-forming nitrite reductase activity. Supporting Evidence: file:DESPS/nrfA/nrfA-uniprot.txt Belongs to the cytochrome c-552 family. |
| GO:0019645 anaerobic electron transport chain | IEA GO_REF:0000118 | ACCEPT | Summary: ACCEPT. NrfA participates in anaerobic respiratory nitrite reduction. Reason: The reviewed UniProt record identifies NrfA as an ammonia-forming cytochrome c nitrite reductase, a periplasmic respiratory enzyme that consumes reduced cytochrome c during anaerobic nitrite reduction. Falcon supports the conserved NrfA reaction but did not recover DESPS-specific electron-partner experiments. Supporting Evidence: file:DESPS/nrfA/nrfA-uniprot.txt Catalyzes the reduction of nitrite to ammonia, consuming six electrons in the process. file:DESPS/nrfA/nrfA-deep-research-falcon.md NrfA-family enzymes catalyze nitrite-to-ammonium reduction as periplasmic respiratory multiheme c-type cytochromes, but the report did not recover DP0344-specific partner or operon experiments. |
| GO:0020037 heme binding | IEA GO_REF:0000120 | ACCEPT | Summary: ACCEPT. NrfA is a multiheme cytochrome c nitrite reductase. Reason: Heme binding is integral to NrfA function because the protein is a multiheme cytochrome c nitrite reductase. The UniProt family assignment and InterPro cytochrome c-552 signatures support this annotation. Supporting Evidence: file:DESPS/nrfA/nrfA-uniprot.txt RecName: Full=Cytochrome c-552; AltName: Full=Ammonia-forming cytochrome c nitrite reductase; EC=1.7.2.2. |
| GO:0030288 outer membrane-bounded periplasmic space | IEA GO_REF:0000118 | ACCEPT | Summary: ACCEPT. The enzyme is periplasmic in Gram-negative bacteria. Reason: NrfA is annotated as a precursor and belongs to the periplasmic cytochrome c nitrite reductase family. The TreeGrafter localization is consistent with the biology of Gram-negative respiratory nitrite reductases. The available support is family-level rather than a DESPS-specific fractionation or localization experiment. Supporting Evidence: file:DESPS/nrfA/nrfA-uniprot.txt Flags: Precursor. file:DESPS/nrfA/nrfA-deep-research-falcon.md The Falcon report describes NrfA as typically soluble periplasmic, but no direct Q6ARF1/DP0344 localization experiment was recovered. |
| GO:0042279 nitrite reductase (cytochrome, ammonia-forming) activity | IEA GO_REF:0000120 | ACCEPT | Summary: ACCEPT. This is the specific molecular function of NrfA. Reason: This is the precise EC-supported activity for NrfA. The reviewed UniProt record gives EC 1.7.2.2 and the ammonia-forming nitrite reductase name, and the HAMAP/InterPro assignments provide node-specific support for the catalytic NrfA call rather than relying on a broad c552 family display label. Falcon did not recover a Q6ARF1 purification or kinetic paper, so the strength is conserved-family/EC evidence. Supporting Evidence: file:DESPS/nrfA/nrfA-uniprot.txt RecName: Full=Cytochrome c-552; AltName: Full=Ammonia-forming cytochrome c nitrite reductase; EC=1.7.2.2. file:DESPS/nrfA/nrfA-uniprot.txt HAMAP; MF_01182; Cytochrom_C552; 1. file:DESPS/nrfA/nrfA-uniprot.txt InterPro; IPR017570; Cyt_c_NO2Rdtase_formate-dep. file:DESPS/nrfA/nrfA-deep-research-falcon.md Recent NrfA synthesis supports the six-electron, eight-proton reduction of nitrite to ammonium by periplasmic multiheme c-type cytochromes; no DP0344-specific enzymology was recovered. |
| GO:0042597 periplasmic space | IEA GO_REF:0000120 | ACCEPT | Summary: ACCEPT. Periplasmic localization is consistent with NrfA function. Reason: This duplicates the more specific outer membrane-bounded periplasmic space annotation but is still biologically consistent with exported NrfA respiratory nitrite reductases. Supporting Evidence: file:DESPS/nrfA/nrfA-uniprot.txt RecName: Full=Cytochrome c-552; AltName: Full=Ammonia-forming cytochrome c nitrite reductase; EC=1.7.2.2. |
| GO:0042128 nitrate assimilation | IEA GO_REF:0000041 | REMOVE | Summary: REMOVE. The UniPathway mapping is not supported for this gene. nrfA is an ammonia-forming cytochrome c nitrite reductase used in anaerobic respiratory nitrite reduction; that is not the same as nitrate assimilation. Reason: Nitrate assimilation is the wrong biological-process endpoint for NrfA. NrfA reduces nitrite to ammonium in anaerobic respiration, whereas nitrate assimilation describes incorporation of nitrate-derived nitrogen into biomass. The correct MF is already present as GO:0042279, and Falcon reinforces the DNRA/respiratory interpretation rather than assimilation. Supporting Evidence: file:DESPS/nrfA/nrfA-uniprot.txt Catalyzes the reduction of nitrite to ammonia, consuming six electrons in the process. file:interpro/panther/PTHR30633/PTHR30633-deep-research-falcon.md Family research warns against treating broad c552 family labels as the propagation unit; catalytic or pathway claims need the relevant phylogenetic node or independent EC/HAMAP/InterPro support. file:DESPS/nrfA/nrfA-deep-research-falcon.md The report frames NrfA as the nitrite-to-ammonium step of DNRA/anaerobic respiration, not nitrate assimilation. |
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