uox encodes uricase (urate oxidase, EC 1.7.3.3), a cofactorless T-fold enzyme that catalyses the first and committed step of oxidative uricolysis, converting urate to 5-hydroxyisourate with consumption of O2 and release of H2O2. It assembles as a homotetramer (a dimer of dimers) with active sites at subunit interfaces, has a KM near 11 uM for urate and is competitively inhibited by xanthine. A C-terminal ARM tripeptide targets it to the peroxisome, where it acts with Urah (5-hydroxyisourate hydrolase) and Urad (OHCU decarboxylase) to produce (S)-allantoin, the soluble nitrogenous end product excreted by fish. The gene is expressed largely in liver; zebrafish lacking it are viable but accumulate urate, unlike hominoids, in which the orthologous gene was pseudogenised.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0019628 urate catabolic process | IBA GO_REF:0000033 | ACCEPT | Summary: Urate catabolic process: Uox catalyses step 1 of 3 of the (S)-allantoin-from-urate pathway, and zebrafish uox null larvae accumulate urate. Reason: The gene product performs a step of the pathway itself, so this is participation in the strict sense, and it is the most specific process term the reaction supports. Loss of uox raises larval urate, confirming flux through this enzyme in vivo (PMID:36553446). Supporting Evidence: file:DANRE/uox/uox-uniprot.txt urate degradation; (S)-allantoin from PMID:36553446 We show that uox KO (uox−/−) larvae have significantly reduced expression of uox in the liver and elevated urate levels at early larval stages. PMID:27922051 Urate oxidase (Uox) catalyses the first reaction of oxidative uricolysis, a |
| GO:0006145 purine nucleobase catabolic process | IBA GO_REF:0000033 | MODIFY | Summary: Purine nucleobase catabolic process: correct in kind (urate derives from purine nucleobase breakdown) but broader than the step Uox performs. Reason: Uox acts on urate, not on a purine nucleobase: its reaction is urate + O2 + H2O = 5-hydroxyisourate + H2O2, the first of three steps converting urate to (S)-allantoin. GO:0019628 states exactly that and is already annotated to this gene, so the IBA is better placed there. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: GRANULARITY MISMATCH Sources checked: PANTHER:PTN000044668 SUPPORTS TRANSFER The uricase family node is correctly inherited by zebrafish uox; only the term chosen at that node is broader than the reaction, since the family's shared step is urate oxidation specifically. UniProtKB:P33282 SUPPORTS TRANSFER Bacillus uricase donor with the same cofactorless T-fold chemistry; it too acts on urate rather than on a purine nucleobase, so the narrower urate catabolic process fits both donor and target. Proposed replacements: urate catabolic process Supporting Evidence: file:DANRE/uox/uox-uniprot.txt Reaction=urate + O2 + H2O = 5-hydroxyisourate + H2O2; file:DANRE/uox/uox-uniprot.txt urate degradation; (S)-allantoin from PMID:27922051 Urate oxidase (Uox) catalyses the first reaction of oxidative uricolysis, a file:DANRE/uox/uox-deep-research-falcon.md catalyzes the **first (rate-limiting) step** of oxidative uricolysis/purine cata |
| GO:0005777 peroxisome | IBA GO_REF:0000033 | ACCEPT | Summary: Peroxisome: zebrafish Uox carries a C-terminal ARM tripeptide matching the PTS1 import signal, and animal uricolysis is peroxisomal, performed by Uox with Urah and Urad. Reason: The targeting signal is present in this very sequence and was noted when the zebrafish enzyme was characterised (PMID:27922051); UniProt independently assigns the peroxisome. All three routes (IBA, IEA, ISS) make the same claim and are graded identically. Supporting Evidence: file:DANRE/uox/uox-uniprot.txt SUBCELLULAR LOCATION: Peroxisome {ECO:0000250|UniProtKB:P09118, PMID:27922051 encodes a protein of 298 aa with a C-terminal tripetide (ARM) corresponding to the type 1 peroxisome-targeting signal PMID:27922051 In animals, uricolysis occurs in peroxisomes by the consecutive action of Uox, HIU hydrolase (Urah), and 2-oxo-4-hydroxy-4-carboxy-5-ureidoimidazoline (OHCU) decarboxylase (Urad). |
| GO:0004846 urate oxidase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Urate oxidase activity assigned automatically from the uricase family signature; the same activity is demonstrated experimentally for this protein. Reason: The automatic assignment agrees with direct measurement on purified zebrafish Uox (PMID:27922051) and with UniProt's EC 1.7.3.3 assignment, so it is correct and at the right level of specificity. Supporting Evidence: file:DANRE/uox/uox-uniprot.txt Catalyzes the oxidation of uric acid to 5-hydroxyisourate, file:DANRE/uox/uox-uniprot.txt Reaction=urate + O2 + H2O = 5-hydroxyisourate + H2O2; PMID:27922051 kinetic assay based on the enzymatic suppression of the spectrophotometric interference of the Uox reaction product |
| GO:0005777 peroxisome | IEA GO_REF:0000044 | ACCEPT | Summary: Peroxisome: zebrafish Uox carries a C-terminal ARM tripeptide matching the PTS1 import signal, and animal uricolysis is peroxisomal, performed by Uox with Urah and Urad. Reason: The targeting signal is present in this very sequence and was noted when the zebrafish enzyme was characterised (PMID:27922051); UniProt independently assigns the peroxisome. All three routes (IBA, IEA, ISS) make the same claim and are graded identically. Supporting Evidence: file:DANRE/uox/uox-uniprot.txt SUBCELLULAR LOCATION: Peroxisome {ECO:0000250|UniProtKB:P09118, PMID:27922051 encodes a protein of 298 aa with a C-terminal tripetide (ARM) corresponding to the type 1 peroxisome-targeting signal PMID:27922051 In animals, uricolysis occurs in peroxisomes by the consecutive action of Uox, HIU hydrolase (Urah), and 2-oxo-4-hydroxy-4-carboxy-5-ureidoimidazoline (OHCU) decarboxylase (Urad). |
| GO:0005777 peroxisome | ISS GO_REF:0000024 | ACCEPT | Summary: Peroxisome: zebrafish Uox carries a C-terminal ARM tripeptide matching the PTS1 import signal, and animal uricolysis is peroxisomal, performed by Uox with Urah and Urad. Reason: The targeting signal is present in this very sequence and was noted when the zebrafish enzyme was characterised (PMID:27922051); UniProt independently assigns the peroxisome. All three routes (IBA, IEA, ISS) make the same claim and are graded identically. Supporting Evidence: file:DANRE/uox/uox-uniprot.txt SUBCELLULAR LOCATION: Peroxisome {ECO:0000250|UniProtKB:P09118, PMID:27922051 encodes a protein of 298 aa with a C-terminal tripetide (ARM) corresponding to the type 1 peroxisome-targeting signal PMID:27922051 In animals, uricolysis occurs in peroxisomes by the consecutive action of Uox, HIU hydrolase (Urah), and 2-oxo-4-hydroxy-4-carboxy-5-ureidoimidazoline (OHCU) decarboxylase (Urad). |
| GO:0046415 urate metabolic process | IMP PMID:36553446 Uricase-Deficient Larval Zebrafish with Elevated Urate Level... | MODIFY | Summary: Urate metabolic process (IMP from the uox CRISPR null): mutant larvae have reduced hepatic uox expression and elevated urate, i.e. loss of urate breakdown. Reason: The phenotype is one-directional - urate accumulates when the enzyme is missing - so the gene acts in the catabolic branch specifically, not in urate metabolism generally. The catabolic child is supported by the same experiment plus the enzyme's measured reaction, and avoids implying a role in urate synthesis. Proposed replacements: urate catabolic process Supporting Evidence: PMID:36553446 We show that uox KO (uox−/−) larvae have significantly reduced expression of uox in the liver and elevated urate levels at early larval stages. PMID:36553446 Here we describe a zebrafish uox null mutant that possesses elevated urate levels at larval stages. file:DANRE/uox/uox-uniprot.txt urate degradation; (S)-allantoin from |
| GO:0004846 urate oxidase activity | IDA PMID:28508122 A Trivalent Enzymatic System for Uricolytic Therapy of HPRT ... | ACCEPT | Summary: Urate oxidase activity of recombinant zebrafish Uox (DrUox), produced and assayed as part of a three-enzyme uricolytic system for enzyme therapy. Reason: The zebrafish protein itself was expressed, purified and its activity measured (and followed through PEGylation), so the molecular function is directly established for this gene product rather than inferred. Supporting Evidence: PMID:28508122 We produced in recombinant form three zebrafish enzymes required in the uricolytic pathway. file:DANRE/uox/uox-uniprot.txt Catalyzes the oxidation of uric acid to 5-hydroxyisourate, file:DANRE/uox/uox-uniprot.txt Reaction=urate + O2 + H2O = 5-hydroxyisourate + H2O2; |
| GO:0004846 urate oxidase activity | IMP PMID:27922051 Catalysis and Structure of Zebrafish Urate Oxidase Provide I... | ACCEPT | Summary: Urate oxidase activity of zebrafish Uox measured kinetically on the purified enzyme (KM = 11 uM for urate, competitive inhibition by xanthine), together with the crystal structure and the effect of the hominoid F216S substitution. Reason: This is the primary biochemical characterisation of the zebrafish enzyme and the source UniProt cites for EC 1.7.3.3 and the kinetic parameters, so the activity is established directly for this gene product. Supporting Evidence: PMID:27922051 kinetic assay based on the enzymatic suppression of the spectrophotometric interference of the Uox reaction product file:DANRE/uox/uox-uniprot.txt KM=11 uM for urate {ECO:0000269|PubMed:27922051}; file:DANRE/uox/uox-uniprot.txt ACTIVITY REGULATION: Competitively inhibited by xanthine. file:DANRE/uox/uox-uniprot.txt Reaction=urate + O2 + H2O = 5-hydroxyisourate + H2O2; |
| GO:0051289 protein homotetramerization | IPI PMID:27922051 Catalysis and Structure of Zebrafish Urate Oxidase Provide I... | KEEP AS NON CORE | Summary: Protein homotetramerization: purified zebrafish Uox is predominantly tetrameric, the T-fold dimer-of-dimers assembly typical of cofactorless uricases, with the active sites at subunit interfaces. Reason: The oligomeric state is experimentally established for this protein (analytical data in PMID:27922051, recorded by UniProt) and is required for a functional active site, but it describes assembly rather than the catalytic work of the gene product, so it is retained as non-core alongside urate oxidase activity. Supporting Evidence: file:DANRE/uox/uox-uniprot.txt SUBUNIT: Homotetramer; dimer of dimers. {ECO:0000269|PubMed:27922051}. PMID:27922051 with a large prevalence of the tetrameric assembly for both proteins |
| GO:0004846 urate oxidase activity | IDA PMID:26349049 The identification of an integral membrane, cytochrome c ura... | ACCEPT | Summary: Urate oxidase activity assayed in vivo in a heterologous host: expression of the soluble zebrafish Uox restored urate degradation in an Agrobacterium fabrum mutant lacking its own urate oxidase, with the H2O2 by-product evidenced by a four-fold catalase increase. Reason: This is a direct functional demonstration of the zebrafish enzyme's catalytic activity, and the catalase response matches the peroxide-generating reaction urate + O2 + H2O = 5-hydroxyisourate + H2O2 that defines GO:0004846. Supporting Evidence: PMID:26349049 the phenotype was fully restored by complementation with a cytosolic Uox from zebrafish. PMID:26349049 Consistent with H2O2 production by zfUox, urate oxidation in the complemented strain caused a four-fold increase of catalase. file:DANRE/uox/uox-uniprot.txt Reaction=urate + O2 + H2O = 5-hydroxyisourate + H2O2; |
| GO:0004846 urate oxidase activity | IDA PMID:27922051 Catalysis and Structure of Zebrafish Urate Oxidase Provide I... | ACCEPT | Summary: Urate oxidase activity of zebrafish Uox measured kinetically on the purified enzyme (KM = 11 uM for urate, competitive inhibition by xanthine), together with the crystal structure and the effect of the hominoid F216S substitution. Reason: This is the primary biochemical characterisation of the zebrafish enzyme and the source UniProt cites for EC 1.7.3.3 and the kinetic parameters, so the activity is established directly for this gene product. Supporting Evidence: PMID:27922051 kinetic assay based on the enzymatic suppression of the spectrophotometric interference of the Uox reaction product file:DANRE/uox/uox-uniprot.txt KM=11 uM for urate {ECO:0000269|PubMed:27922051}; file:DANRE/uox/uox-uniprot.txt ACTIVITY REGULATION: Competitively inhibited by xanthine. file:DANRE/uox/uox-uniprot.txt Reaction=urate + O2 + H2O = 5-hydroxyisourate + H2O2; |
| GO:0019628 urate catabolic process | IDA PMID:27922051 Catalysis and Structure of Zebrafish Urate Oxidase Provide I... | ACCEPT | Summary: Urate catabolic process: Uox catalyses step 1 of 3 of the (S)-allantoin-from-urate pathway, and zebrafish uox null larvae accumulate urate. Reason: The gene product performs a step of the pathway itself, so this is participation in the strict sense, and it is the most specific process term the reaction supports. Loss of uox raises larval urate, confirming flux through this enzyme in vivo (PMID:36553446). The IDA rests on the assayed zebrafish enzyme (PMID:27922051). Supporting Evidence: file:DANRE/uox/uox-uniprot.txt urate degradation; (S)-allantoin from PMID:36553446 We show that uox KO (uox−/−) larvae have significantly reduced expression of uox in the liver and elevated urate levels at early larval stages. PMID:27922051 Urate oxidase (Uox) catalyses the first reaction of oxidative uricolysis, a |
| GO:0004846 urate oxidase activity | IBA GO_REF:0000033 | ACCEPT | Summary: Urate oxidase activity inherited from the cofactorless uricase (T-fold) family node; zebrafish Uox is a canonical member with demonstrated activity. Reason: The PAINT node covers the classical Uox family, whose eukaryotic members share the cofactorless T-fold catalysing urate oxidation, and the target is inside that clade with its own experimental evidence (PMID:27922051, PMID:26349049) - the target appearing among the descendant evidences is expected, not circular. Supporting Evidence: PMID:27922051 Urate oxidase (Uox) catalyses the first reaction of oxidative uricolysis, a PMID:26349049 the phenotype was fully restored by complementation with a cytosolic Uox from zebrafish. file:DANRE/uox/uox-uniprot.txt Reaction=urate + O2 + H2O = 5-hydroxyisourate + H2O2; |
| GO:0019628 urate catabolic process | IEA GO_REF:0000120 | ACCEPT | Summary: Urate catabolic process: Uox catalyses step 1 of 3 of the (S)-allantoin-from-urate pathway, and zebrafish uox null larvae accumulate urate. Reason: The gene product performs a step of the pathway itself, so this is participation in the strict sense, and it is the most specific process term the reaction supports. Loss of uox raises larval urate, confirming flux through this enzyme in vivo (PMID:36553446). The automatic assignment (UniPathway/combined IEA) matches the experimental rows and is graded identically. Supporting Evidence: file:DANRE/uox/uox-uniprot.txt urate degradation; (S)-allantoin from PMID:36553446 We show that uox KO (uox−/−) larvae have significantly reduced expression of uox in the liver and elevated urate levels at early larval stages. PMID:27922051 Urate oxidase (Uox) catalyses the first reaction of oxidative uricolysis, a |
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Download this section (compressed HTML)Q: Is zebrafish Uox imported into peroxisomes in vivo via its ARM/PTS1 tripeptide, and does mislocalisation alter urate handling?
Q: Does the H2O2 generated by Uox contribute measurably to peroxisomal oxidative load in zebrafish liver, given catalase co-localisation?
Experiment: Image tagged Uox against a peroxisomal marker in zebrafish liver, with and without the C-terminal ARM tripeptide.
Hypothesis: The ARM tripeptide is necessary and sufficient for peroxisomal import of zebrafish Uox.
Experiment: Measure allantoin and urate in uox-/- versus wild-type larvae and after re-expression of wild-type or F216S Uox.
Hypothesis: Urate accumulation in uox nulls reflects loss of the first uricolytic step and is rescued by catalytically competent Uox.
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