Gulo encodes mouse L-gulonolactone oxidase, an FAD-dependent oxygen-dependent oxidoreductase that catalyzes the terminal step of L-ascorbate biosynthesis by oxidizing L-gulono-1,4-lactone with molecular oxygen to produce L-ascorbate and hydrogen peroxide. The protein is highly expressed in liver and is associated with the microsomal/endoplasmic reticulum membrane.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0016491 oxidoreductase activity | IBA GO_REF:0000033 | MODIFY | Summary: Gulo has oxidoreductase activity, but this term is too general for the established enzyme. Reason: Phylogenetic and experimental evidence supports the specific L-gulonolactone oxidase activity rather than the broad oxidoreductase parent term. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: GRANULARITY MISMATCH Sources checked: PANTHER:PTN000356408 SUPPORTS TRANSFER The node places Gulo in the FAD-dependent aldonolactone oxidoreductase group, which is correct; "oxidoreductase activity" is simply the root-level parent of the specific activity rather than a mis-transfer. MGI:MGI:1353434 · mouse Gulo (the review target itself) SUPPORTS TRANSFER The target's own MGI record is one of the IBD seeds - not the only one: this row's WITH/FROM also carries CGD:CAL0000174500, RGD:620701, SGD:S000004551, TAIR:locus:2097865, UniProtKB:P9WIT3 and UniProtKB:Q57ZU1. The span reaches fungi and plants from the CGD/SGD/TAIR prefixes alone, and bacteria from P9WIT3, which interpro/panther/PTHR43762/PTHR43762-entries.csv resolves as Mycobacterium tuberculosis L-gulono-1,4-lactone dehydrogenase (gene Rv1771) - a checkable identification rather than an assumed one. That span is consistent with a root-level oxidoreductase term being inherited very deep. The remaining five are cited by identifier only: they do not resolve against the local caches and no claim is made here about which proteins they are. The target's own presence still matters, because mouse Gulo is a functional L-gulonolactone oxidase, unlike the primate pseudogene, so the specific activity term is warranted for this species. Proposed replacements: L-gulonolactone oxidase activity Supporting Evidence: UniProtKB:P58710 Oxidizes L-gulono-1,4-lactone to hydrogen peroxide and L- xylo-hexulonolactone which spontaneously isomerizes to L-ascorbate. file:mouse/Gulo/Gulo-deep-research-falcon.md Enzyme: L‑gulonolactone oxidase (EC 1.1.3.8), terminal ascorbate biosynthesis step: L‑gulono‑1,4‑lactone + O2 → L‑ascorbate + H2O2; FAD‑dependent AlOR enzyme with N‑terminal FAD‑binding region and C‑terminal HWXK motif; integral ER/microsomal membrane protein with luminally oriented active site; predominant tissue locus in mammalian liver |
| GO:0003885 D-arabinono-1,4-lactone oxidase activity | IEA GO_REF:0000002 | MODIFY | Summary: The InterPro-mapped activity has the wrong physiological substrate for mouse Gulo. Reason: Mouse Gulo is experimentally supported as L-gulono-1,4-lactone oxidase in vitamin C biosynthesis; D-arabinono-1,4-lactone oxidase activity is not the appropriate specific activity for this mammalian enzyme. Proposed replacements: L-gulonolactone oxidase activity Supporting Evidence: PMID:14962674 expressed a functional enzyme as measured by the conversion of l-gulono-gamma-lactone to ascorbic acid in cell-free extracts UniProtKB:P58710 Reaction=L-gulono-1,4-lactone + O2 = L-ascorbate + H2O2 + H(+) |
| GO:0005789 endoplasmic reticulum membrane | IEA GO_REF:0000044 | ACCEPT | Summary: Gulo is an ER/microsomal single-pass membrane protein. Reason: UniProt records Gulo as a microsomal and ER membrane protein, and mouse liver microsomal assays place the ascorbate-producing activity in the microsomal fraction. Supporting Evidence: UniProtKB:P58710 Microsome membrane {ECO:0000250}; Single-pass membrane protein {ECO:0000250}. Endoplasmic reticulum membrane {ECO:0000250}; Single-pass membrane protein {ECO:0000250}. PMID:10606751 microsomal ascorbate production from p-nitrophenyl glucuronide, D-glucuronic acid or gulonolactone in the liver |
| GO:0016020 membrane | IEA GO_REF:0000002 | MODIFY | Summary: Membrane association is correct but should be represented more specifically as ER membrane. Reason: The generic membrane term is a true but low-information ancestor of the supported ER/microsomal membrane localization. Proposed replacements: endoplasmic reticulum membrane Supporting Evidence: UniProtKB:P58710 Endoplasmic reticulum membrane {ECO:0000250}; Single-pass membrane protein {ECO:0000250}. |
| GO:0016491 oxidoreductase activity | IEA GO_REF:0000120 | MODIFY | Summary: General oxidoreductase activity is too broad for Gulo. Reason: Automated annotation should use the specific, experimentally supported L-gulonolactone oxidase activity where possible. Proposed replacements: L-gulonolactone oxidase activity Supporting Evidence: PMID:14962674 expressed a functional enzyme as measured by the conversion of l-gulono-gamma-lactone to ascorbic acid in cell-free extracts |
| GO:0016899 oxidoreductase activity, acting on the CH-OH group of donors, oxygen as acceptor | IEA GO_REF:0000002 | MODIFY | Summary: This oxidoreductase superclass term is broader than Gulo's known specific activity. Reason: Gulo is the FAD-dependent L-gulono-1,4-lactone oxidase in the terminal step of ascorbate biosynthesis, so the specific catalytic term is preferred over this parent term. Proposed replacements: L-gulonolactone oxidase activity Supporting Evidence: UniProtKB:P58710 Reaction=L-gulono-1,4-lactone + O2 = L-ascorbate + H2O2 + H(+) |
| GO:0019853 L-ascorbic acid biosynthetic process | IEA GO_REF:0000043 | ACCEPT | Summary: Gulo functions in L-ascorbic acid biosynthesis. Reason: Gulo catalyzes the terminal reaction of the L-ascorbate biosynthetic pathway, and loss of Gulo makes mice vitamin C dependent. Supporting Evidence: UniProtKB:P58710 L-ascorbate biosynthesis via UDP-alpha-D-glucuronate pathway; L-ascorbate from UDP-alpha-D-glucuronate: step 4/4. PMID:10639167 By inactivating the gene for L-gulono-gamma-lactone oxidase, a key enzyme in ascorbic acid synthesis, we have generated mice that, like humans, depend on dietary vitamin C. |
| GO:0050105 L-gulonolactone oxidase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Gulo catalyzes L-gulono-1,4-lactone oxidation. Reason: The automated term exactly matches the experimentally supported enzymatic activity and UniProt/Rhea catalytic reaction for mouse Gulo. Supporting Evidence: UniProtKB:P58710 Reaction=L-gulono-1,4-lactone + O2 = L-ascorbate + H2O2 + H(+) |
| GO:0050660 flavin adenine dinucleotide binding | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: FAD binding is supported but is a cofactor property rather than the core activity. Reason: Gulo is an FAD-containing flavoprotein, but the core molecular function is L-gulonolactone oxidase activity. Supporting Evidence: PMID:14962674 overexpressed an FAD-containing protein UniProtKB:P58710 Name=FAD; Xref=ChEBI:CHEBI:57692 |
| GO:0071949 FAD binding | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: FAD binding is supported but secondary to the catalytic activity. Reason: The InterPro FAD-binding annotation is consistent with the FAD-dependent enzyme family and experimental expression of an FAD-containing protein, but cofactor binding is not the core function to emphasize. Supporting Evidence: file:mouse/Gulo/Gulo-deep-research-falcon.md FAD‑dependent AlOR enzyme with N‑terminal FAD‑binding region and C‑terminal HWXK motif |
| GO:0050105 L-gulonolactone oxidase activity | ISO GO_REF:0000096 | ACCEPT | Summary: Orthology transfer supports Gulo's specific L-gulonolactone oxidase activity. Reason: The transferred activity agrees with direct mouse Gulo evidence and the conserved function of Gulo orthologs. Supporting Evidence: PMID:14962674 expressed a functional enzyme as measured by the conversion of l-gulono-gamma-lactone to ascorbic acid in cell-free extracts |
| GO:0050105 L-gulonolactone oxidase activity | IDA PMID:10606751 Different induction of gulonolactone oxidase in aromatic hyd... | ACCEPT | Summary: Mouse liver microsomes show Gulo-associated ascorbate-producing activity from gulonolactone. Reason: The study measured Gulo mRNA and microsomal ascorbate production from gulonolactone in mouse liver, consistent with L-gulonolactone oxidase activity. Supporting Evidence: PMID:10606751 The mRNA level of gulonolactone oxidase and the microsomal ascorbate production from p-nitrophenyl glucuronide, D-glucuronic acid or gulonolactone in the liver of Ah-responsive and Ah-unresponsive mice were compared. |
| GO:0050105 L-gulonolactone oxidase activity | IMP PMID:10606751 Different induction of gulonolactone oxidase in aromatic hyd... | ACCEPT | Summary: Genetic/regulatory differences in Gulo expression track with microsomal ascorbate production. Reason: AhR-responsive mice had higher Gulo mRNA and higher microsomal ascorbate production from gulonolactone, supporting Gulo's role in the activity. Supporting Evidence: PMID:10606751 In Ah-responsive mice, these parameters were higher originally, and they further increased upon in vivo addition of 3-methylcholanthrene, while in Ah-unresponsive mice the treatment was not effective. |
| GO:0050105 L-gulonolactone oxidase activity | IMP PMID:20410296 Ascorbate synthesis pathway: dual role of ascorbate in bone ... | UNDECIDED | Summary: The term is correct for Gulo, but this reference is indirect for Gulo activity. Reason: PMID:20410296 mainly addresses upstream Akr1a4/Akr1b3 enzymes in the ascorbate biosynthesis pathway, not direct Gulo L-gulonolactone oxidase activity. Other GO:0050105 annotations with direct Gulo evidence remain accepted, but this specific row should not be accepted from this PMID. Supporting Evidence: PMID:20410296 Using mouse gene knock-out models, we identify aldehyde reductase (EC 1.1.1.2, Akr1a4 (GR)) and aldose reductase (EC 1.1.1.21, Akr1b3 (AR)) as the enzymes responsible for conversion of D-glucuronate to L-gulonate, a key step in the ascorbate (ASC) synthesis pathway in mice. |
| GO:0019853 L-ascorbic acid biosynthetic process | IDA PMID:14962674 Functional rescue of vitamin C synthesis deficiency in human... | ACCEPT | Summary: Heterologous expression of murine Gulo restores the terminal enzymatic step of vitamin C synthesis. Reason: Murine Gulo expression produced a functional enzyme that converted L-gulono-gamma-lactone to ascorbic acid, directly supporting its pathway role. Supporting Evidence: PMID:14962674 expressed a functional enzyme as measured by the conversion of l-gulono-gamma-lactone to ascorbic acid in cell-free extracts |
| GO:0050105 L-gulonolactone oxidase activity | IDA PMID:14962674 Functional rescue of vitamin C synthesis deficiency in human... | ACCEPT | Summary: Murine Gulo directly catalyzes conversion of L-gulono-gamma-lactone to ascorbic acid. Reason: Cell-free extracts expressing murine Gulo converted L-gulono-gamma-lactone to ascorbic acid. Supporting Evidence: PMID:14962674 expressed a functional enzyme as measured by the conversion of l-gulono-gamma-lactone to ascorbic acid in cell-free extracts |
| GO:0050660 flavin adenine dinucleotide binding | IDA PMID:14962674 Functional rescue of vitamin C synthesis deficiency in human... | KEEP AS NON CORE | Summary: Recombinant murine Gulo is FAD-containing. Reason: Experimental expression supports FAD binding, but this cofactor-binding property is secondary to the enzyme's core L-gulonolactone oxidase activity. Supporting Evidence: PMID:14962674 overexpressed an FAD-containing protein |
| GO:0019853 L-ascorbic acid biosynthetic process | IMP PMID:10639167 Aortic wall damage in mice unable to synthesize ascorbic aci... | ACCEPT | Summary: Gulo is required for endogenous ascorbic acid synthesis in mice. Reason: Inactivation of Gulo makes mice dependent on dietary vitamin C, showing that Gulo acts in L-ascorbate biosynthesis in vivo. Supporting Evidence: PMID:10639167 By inactivating the gene for L-gulono-gamma-lactone oxidase, a key enzyme in ascorbic acid synthesis, we have generated mice that, like humans, depend on dietary vitamin C. |
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Download this section (compressed HTML)Q: For mouse Gulo, is the catalytic site experimentally confirmed to face the ER lumen, or is that orientation inferred from mammalian GULO topology and microsomal studies?
Suggested experts: Ha MN, Bánhegyi G
Q: Does mouse Gulo have measurable physiological activity toward alternative aldonolactone substrates, or is L-gulono-1,4-lactone the only relevant in vivo substrate?
Suggested experts: Schellhorn HE
Experiment: Express epitope-tagged mouse Gulo in hepatocyte-derived cells and combine selective membrane permeabilization, protease protection, and ER-lumenal marker colocalization with an L-gulono-1,4-lactone activity assay.
Hypothesis: Mouse Gulo's active site is oriented toward the ER lumen while the protein is anchored in the ER/microsomal membrane.
Type: subcellular topology and enzyme activity assay
Experiment: Purify recombinant mouse Gulo or enrich microsomal Gulo and compare kinetic parameters for L-gulono-1,4-lactone versus D-arabinono-1,4-lactone and related aldonolactones under matched assay conditions.
Hypothesis: L-gulono-1,4-lactone is the physiologically preferred substrate for mouse Gulo.
Type: comparative enzyme kinetics
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