Gsta1 encodes rat glutathione S-transferase alpha-1 (GST A1-1, also called GST Ya-1 or ligandin), a cytosolic alpha-class glutathione transferase (EC 2.5.1.18) that works as a homodimer or as a heterodimer with GSTA2. Its principal activity is phase II detoxification, in which it catalyses nucleophilic attack by the sulfur of reduced glutathione on the electrophilic centres of a wide range of exogenous and endogenous compounds, producing more soluble S-substituted glutathione conjugates that are exported and processed through the mercapturic acid pathway. The same active site supports several secondary, glutathione-dependent activities of the alpha class, including conjugation of the cyclopentenone prostaglandins A2 and J2, isomerisation of D5-androstene-3,17-dione to D4-androstene-3,17-dione, and glutathione peroxidase activity toward fatty acid hydroperoxides such as 13-HPODE, linking the enzyme to prostaglandin turnover, steroid metabolism, and oxidised-lipid clearance. Independently of catalysis, the Ya homodimer is the classical hepatic ligandin, binding organic anions, bilirubin, steroid hormones, carcinogens, and azo dyes, and it sequesters the dinitrosyl-diglutathionyl-iron complex. Gsta1 is most abundant in liver cytosol and is induced with the wider Nrf2/antioxidant-response-element electrophile defence programme.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005829 cytosol | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: cytosol is retained as useful context for Gsta1, but it is not the defining core function (IBA, GO_REF:0000033). Reason: cytosol records where Gsta1 has been observed, but localization does not define the gene product's primary activity. Supporting Evidence: UniProtKB:P00502 SUBCELLULAR LOCATION: Cytoplasm. |
| GO:0004364 glutathione transferase activity | IBA GO_REF:0000033 | ACCEPT | Summary: Gsta1's glutathione conjugation of electrophilic endogenous and xenobiotic substrates supports retaining glutathione transferase activity as a direct annotation (IBA, GO_REF:0000033). Reason: glutathione transferase activity is a specific catalytic activity matching Gsta1's documented role in glutathione conjugation of electrophilic endogenous and xenobiotic substrates. Supporting Evidence: UniProtKB:P00502 Reaction=RX + glutathione = an S-substituted glutathione + a halide anion + H(+) file:rat/Gsta1/Gsta1-deep-research-falcon.md **Glutathione S-transferases (GSTs)** are enzymes best known for catalyzing **phase II detoxification** reactions by promoting the **conjugation of reduced glutathione (GSH)** to a wide range of **electrophilic** endogenous and exogenous compounds, thereby increasing their solubility and facilitating elimination. |
| GO:0006749 glutathione metabolic process | IBA GO_REF:0000033 | ACCEPT | Summary: Gsta1's glutathione conjugation of electrophilic endogenous and xenobiotic substrates supports retaining glutathione metabolic process as a direct annotation (IBA, GO_REF:0000033). Reason: glutathione metabolic process is a direct metabolic process expected from Gsta1's documented role in glutathione conjugation of electrophilic endogenous and xenobiotic substrates. Supporting Evidence: UniProtKB:P00502 Reaction=RX + glutathione = an S-substituted glutathione + a halide anion + H(+) |
| GO:0006805 xenobiotic metabolic process | IBA GO_REF:0000033 | ACCEPT | Summary: Gsta1's glutathione conjugation of electrophilic endogenous and xenobiotic substrates supports retaining xenobiotic metabolic process as a direct annotation (IBA, GO_REF:0000033). Reason: xenobiotic metabolic process is a direct metabolic process expected from Gsta1's documented role in glutathione conjugation of electrophilic endogenous and xenobiotic substrates. Supporting Evidence: UniProtKB:P00502 FUNCTION: Glutathione S-transferase that catalyzes the nucleophilic attack of the sulfur atom of glutathione on the electrophilic groups of a wide range of exogenous and endogenous compounds (Probable). file:rat/Gsta1/Gsta1-deep-research-falcon.md **Glutathione S-transferases (GSTs)** are enzymes best known for catalyzing **phase II detoxification** reactions by promoting the **conjugation of reduced glutathione (GSH)** to a wide range of **electrophilic** endogenous and exogenous compounds, thereby increasing their solubility and facilitating elimination. |
| GO:0004364 glutathione transferase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Gsta1's glutathione conjugation of electrophilic endogenous and xenobiotic substrates supports retaining glutathione transferase activity as a direct annotation (IEA, GO_REF:0000120). Reason: glutathione transferase activity is a specific catalytic activity matching Gsta1's documented role in glutathione conjugation of electrophilic endogenous and xenobiotic substrates. Supporting Evidence: UniProtKB:P00502 Reaction=RX + glutathione = an S-substituted glutathione + a halide anion + H(+) |
| GO:0004769 steroid Delta-isomerase activity | IEA GO_REF:0000116 | KEEP AS NON CORE | Summary: steroid Delta-isomerase activity is retained as useful context for Gsta1, but it is not the defining core function (IEA, GO_REF:0000116). Reason: steroid Delta-isomerase activity is biologically compatible with Gsta1, but it is contextual or broader than the direct role in glutathione conjugation of electrophilic endogenous and xenobiotic substrates. Supporting Evidence: UniProtKB:P00502 Reaction=androst-5-ene-3,17-dione = androst-4-ene-3,17-dione file:rat/Gsta1/Gsta1-deep-research-falcon.md - **Isomerase** and other activities reported across GSTs (class-level statement) (stoian2025modulationofglutathionestransferase pages 1-2) |
| GO:0005737 cytoplasm | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: cytoplasm is retained as useful context for Gsta1, but it is not the defining core function (IEA, GO_REF:0000044). Reason: cytoplasm records where Gsta1 has been observed, but localization does not define the gene product's primary activity. Supporting Evidence: UniProtKB:P00502 SUBCELLULAR LOCATION: Cytoplasm. |
| GO:0047066 phospholipid-hydroperoxide glutathione peroxidase activity | IEA GO_REF:0000116 | KEEP AS NON CORE | Summary: phospholipid-hydroperoxide glutathione peroxidase activity is retained as useful context for Gsta1, but it is not the defining core function (IEA, GO_REF:0000116). Reason: The phospholipid-hydroperoxide specificity is adjudicated here. The rat UniProt basis is the free-fatty-acid hydroperoxide reaction (13-HPODE, RHEA:48888), but the phospholipid-hydroperoxide half of this term is directly supported by the human alpha-class ortholog hGSTA1-1, whose recombinant enzyme reduces phosphatidylcholine and phosphatidylethanolamine hydroperoxides with high catalytic efficiency (PMID:10395737), matching the treatment of the Gsta2 GO:0047066 rows. The term is therefore retained as a genuine but secondary alpha-class peroxidase activity, not the defining glutathione-conjugation function. Supporting Evidence: PMID:10395737 Both isozymes had remarkably high peroxidase activity toward fatty acid hydroperoxides, phospholipid hydroperoxides, and cumene hydroperoxide. PMID:10395737 catalytic efficiency (kcat/Km) of hGSTA1-1 for phosphatidylcholine (PC) hydroperoxide and phosphatidylethanolamine (PE) hydroperoxide was found to be 181.3 and 199.6 s-1 mM-1 UniProtKB:P00502 Through its glutathione-dependent peroxidase activity toward the fatty acid hydroperoxide (13S)-hydroperoxy-(9Z,11E)-octadecadienoate/13-HPODE it is also involved in the metabolism of oxidized linoleic acid (By similarity). file:rat/Gsta1/Gsta1-deep-research-falcon.md In mammalian systems, **A-class (alpha) GSTs** are noted for (i) high activity in detoxification pathways and (ii) **selenium-independent glutathione peroxidase (GPx)-like activity**, including reduction of lipid and sterol hydroperoxides in membranes. Anionic A-class enzymes are described as efficient catalysts for conjugation of lipid-derived electrophiles such as **4-hydroxynonenal (4-HNE)**. |
| GO:0098869 cellular oxidant detoxification | IEA GO_REF:0000108 | KEEP AS NON CORE | Summary: cellular oxidant detoxification is retained as useful context for Gsta1, but it is not the defining core function (IEA, GO_REF:0000108). Reason: cellular oxidant detoxification is biologically compatible with Gsta1, but it is contextual or broader than the direct role in glutathione conjugation of electrophilic endogenous and xenobiotic substrates. Supporting Evidence: UniProtKB:P00502 Through its glutathione-dependent peroxidase activity toward the fatty acid hydroperoxide (13S)-hydroperoxy-(9Z,11E)-octadecadienoate/13-HPODE it is also involved in the metabolism of oxidized linoleic acid (By similarity). file:rat/Gsta1/Gsta1-deep-research-falcon.md In mammalian systems, **A-class (alpha) GSTs** are noted for (i) high activity in detoxification pathways and (ii) **selenium-independent glutathione peroxidase (GPx)-like activity**, including reduction of lipid and sterol hydroperoxides in membranes. Anionic A-class enzymes are described as efficient catalysts for conjugation of lipid-derived electrophiles such as **4-hydroxynonenal (4-HNE)**. |
| GO:0005829 cytosol | ISO GO_REF:0000121 | KEEP AS NON CORE | Summary: cytosol is retained as useful context for Gsta1, but it is not the defining core function (ISO, GO_REF:0000121; donor mouse Gsta2, MGI:MGI:95863). Reason: cytosol records where Gsta1 has been observed, but localization does not define the gene product's primary activity. The donor is mouse Gsta2 (MGI:MGI:95863); although rodent alpha-class symbol matching is not a safe orthology call, the cytosolic location is independently established for rat GSTA1 by direct assay (IDA, PMID:17112229) and by the UniProt subcellular location, so the transfer is not load-bearing. Supporting Evidence: UniProtKB:P00502 SUBCELLULAR LOCATION: Cytoplasm. |
| GO:0004364 glutathione transferase activity | EXP PMID:11119643 Localization of the C-terminus of rat glutathione S-transfer... | ACCEPT | Summary: Gsta1's glutathione conjugation of electrophilic endogenous and xenobiotic substrates supports retaining glutathione transferase activity as a direct annotation (EXP, PMID:11119643). Reason: glutathione transferase activity is a specific catalytic activity matching Gsta1's documented role in glutathione conjugation of electrophilic endogenous and xenobiotic substrates. Supporting Evidence: PMID:11119643 Localization of the C-terminus of rat glutathione S-transferase A1-1 UniProtKB:P00502 Reaction=RX + glutathione = an S-substituted glutathione + a halide |
| GO:0005739 mitochondrion | ISO GO_REF:0000121 | MARK AS OVER ANNOTATED | Summary: mitochondrion is treated as over-annotation because it is a symbol-matched ISO transfer from mouse and is not supported by any rat observation (ISO, GO_REF:0000121). Reason: mitochondrion was not observed for rat Gsta1; it enters solely by ISO transfer from mouse MGI:MGI:95863, and UniProt records only Cytoplasm as the subcellular location for P00502. Propagation Review Root cause: PROPAGATION BAD Failure modes: COMPARTMENT OR COMPLEX MISMATCH WRONG ORTHOLOG OR PARALOG Sources checked: MGI:MGI:95863 · mouse Gsta2 SUPPORTS SOURCE BUT NOT TARGET Rodent alpha-class GST symbols are not 1:1 orthologous between mouse and rat, so symbol-matched transfer from mouse Gsta2 to rat Gsta1 (P00502) is unsafe, and a compartment call is the kind of claim least likely to survive that step. The rat record carries only Cytoplasm as its subcellular location, and no rat experiment places GSTA1 in mitochondria. Note that this same donor is trusted elsewhere in this file for GO:0004364 and GO:0005829: those two are independently confirmed for rat by direct assay (IDA, PMID:15152091 and PMID:17112229 respectively), so the transfer is not load-bearing there. For mitochondrion there is no such independent rat evidence, and the donor is the sole support. Supporting Evidence: UniProtKB:P00502 SUBCELLULAR LOCATION: Cytoplasm. |
| GO:0004364 glutathione transferase activity | ISO GO_REF:0000121 | ACCEPT | Summary: Gsta1's glutathione conjugation of electrophilic endogenous and xenobiotic substrates supports retaining glutathione transferase activity as a direct annotation (ISO, GO_REF:0000121). Reason: glutathione transferase activity is a specific catalytic activity matching Gsta1's documented role in glutathione conjugation of electrophilic endogenous and xenobiotic substrates. Supporting Evidence: UniProtKB:P00502 Reaction=RX + glutathione = an S-substituted glutathione + a halide anion + H(+) |
| GO:0035731 dinitrosyl-iron complex binding | IPI PMID:17197701 Electrostatic association of glutathione transferase to the ... | KEEP AS NON CORE | Summary: dinitrosyl-iron complex binding is retained as useful context for Gsta1, but it is not the defining core function (IPI, PMID:17197701). Reason: dinitrosyl-iron complex binding records substrate, cofactor, or quaternary-structure context for Gsta1, but the curated core function is glutathione conjugation of electrophilic endogenous and xenobiotic substrates. Supporting Evidence: PMID:17197701 The discovery that the dinitrosyl-diglutathionyl-iron complex binds tightly to Alpha class GSTs in rat hepatocytes |
| GO:0004769 steroid Delta-isomerase activity | ISS GO_REF:0000024 | KEEP AS NON CORE | Summary: steroid Delta-isomerase activity is retained as useful context for Gsta1, but it is not the defining core function (ISS, GO_REF:0000024). Reason: steroid Delta-isomerase activity is biologically compatible with Gsta1, but it is contextual or broader than the direct role in glutathione conjugation of electrophilic endogenous and xenobiotic substrates. Supporting Evidence: UniProtKB:P00502 Reaction=androst-5-ene-3,17-dione = androst-4-ene-3,17-dione |
| GO:0006693 prostaglandin metabolic process | ISS GO_REF:0000024 | KEEP AS NON CORE | Summary: prostaglandin metabolic process is retained as useful context for Gsta1, but it is not the defining core function (ISS, GO_REF:0000024). Reason: prostaglandin metabolic process is biologically compatible with Gsta1, but it is contextual or broader than the direct role in glutathione conjugation of electrophilic endogenous and xenobiotic substrates. Supporting Evidence: UniProtKB:P00502 Involved in the formation of glutathione conjugates of both prostaglandin A2 (PGA2) and prostaglandin J2 (PGJ2). |
| GO:1901687 glutathione derivative biosynthetic process | ISS GO_REF:0000024 | ACCEPT | Summary: Gsta1's glutathione conjugation of electrophilic endogenous and xenobiotic substrates supports retaining glutathione derivative biosynthetic process as a direct annotation (ISS, GO_REF:0000024). Reason: glutathione derivative biosynthetic process is a direct metabolic process expected from Gsta1's documented role in glutathione conjugation of electrophilic endogenous and xenobiotic substrates. Supporting Evidence: UniProtKB:P00502 Involved in the formation of glutathione conjugates of both prostaglandin A2 (PGA2) and prostaglandin J2 (PGJ2). |
| GO:0009617 response to bacterium | ISO GO_REF:0000121 | MARK AS OVER ANNOTATED | Summary: response to bacterium is treated as over-annotation because it reflects context or consequence rather than Gsta1's direct role (ISO, GO_REF:0000121). Reason: response to bacterium reflects exposure, expression, phenotype, or downstream pathway context rather than the direct Gsta1 role in glutathione conjugation of electrophilic endogenous and xenobiotic substrates. Propagation Review Root cause: PROPAGATION BAD Failure modes: WRONG ORTHOLOG OR PARALOG CONTEXT OR TISSUE MISMATCH Sources checked: MGI:MGI:95863 · mouse Gsta2 SUPPORTS SOURCE BUT NOT TARGET Two problems compound here. Rodent alpha-class GST symbols are not 1:1 orthologous between mouse and rat, so a symbol-matched transfer from mouse Gsta2 to rat Gsta1 (P00502) already crosses paralogues. The donor evidence is also context-bound: it records a response measured under bacterial challenge in mouse, and neither that induction nor any role for rat Gsta1 in it has been shown in rat. |
| GO:0004364 glutathione transferase activity | IDA PMID:15152091 Heterodimers of wild-type and subunit interface mutant enzym... | ACCEPT | Summary: Gsta1's glutathione conjugation of electrophilic endogenous and xenobiotic substrates supports retaining glutathione transferase activity as a direct annotation (IDA, PMID:15152091). Reason: glutathione transferase activity is a specific catalytic activity matching Gsta1's documented role in glutathione conjugation of electrophilic endogenous and xenobiotic substrates. Supporting Evidence: PMID:15152091 Heterodimers of rat glutathione S-transferase A1-1 were formed using one wild-type subunit and one subunit with a mutation at the interface to evaluate whether the subunits are interactive or independent. PMID:15152091 The specific activities of the heterodimer were compared with those of the two homodimers to determine whether the less active, mutant subunit communicates with the other subunit. |
| GO:0004364 glutathione transferase activity | IDA PMID:17112229 Site-specific arylation of rat glutathione s-transferase A1 ... | ACCEPT | Summary: Gsta1's glutathione conjugation of electrophilic endogenous and xenobiotic substrates supports retaining glutathione transferase activity as a direct annotation (IDA, PMID:17112229). Reason: glutathione transferase activity is a specific catalytic activity matching Gsta1's documented role in glutathione conjugation of electrophilic endogenous and xenobiotic substrates. The PMID:17112229 quote establishes the rat alpha-class subunits being isolated from liver cytosol, not catalysis; the catalytic activity itself is independently documented by the UniProt CATALYTIC ACTIVITY record, and the IDA row is retained by deferral to the RGD curator (who read the full text). Supporting Evidence: UniProtKB:P00502 Reaction=RX + glutathione = an S-substituted glutathione + a halide anion + H(+) PMID:17112229 In this work glutathione S-transferase (GST), a well-known and abundant BB-target protein, was isolated from liver cytosol of rats treated with 14C-BB by use of a glutathione (GSH)-agarose affinity column and further resolved by reverse-phase high-performance liquid chromatography (HPLC) into subunits M1, M2, A1, A2 and A3. |
| GO:0005829 cytosol | IDA PMID:17112229 Site-specific arylation of rat glutathione s-transferase A1 ... | KEEP AS NON CORE | Summary: cytosol is retained as useful context for Gsta1, but it is not the defining core function (IDA, PMID:17112229). Reason: cytosol records where Gsta1 has been observed, but localization does not define the gene product's primary activity. Supporting Evidence: PMID:17112229 In this work glutathione S-transferase (GST), a well-known and abundant BB-target protein, was isolated from liver cytosol of rats treated with 14C-BB by use of a glutathione (GSH)-agarose affinity column and further resolved by reverse-phase high-performance liquid chromatography (HPLC) into subunits M1, M2, A1, A2 and A3. file:rat/Gsta1/Gsta1-deep-research-falcon.md The evidence base supports the view that GSTs are primarily **cytosolic enzymes**, consistent with cytosolic GST fold proteins and classic phase II metabolism. |
| GO:0042178 xenobiotic catabolic process | IDA PMID:17112229 Site-specific arylation of rat glutathione s-transferase A1 ... | ACCEPT | Summary: Gsta1's glutathione conjugation of electrophilic endogenous and xenobiotic substrates supports retaining xenobiotic catabolic process as a direct annotation (IDA, PMID:17112229). Reason: xenobiotic catabolic process is a direct metabolic process expected from Gsta1's documented role in glutathione conjugation of electrophilic endogenous and xenobiotic substrates. The PMID:17112229 quote establishes the rat alpha-class subunits being isolated as bromobenzene-target proteins from liver cytosol, not the conjugation chemistry itself; the catalytic/xenobiotic-conjugation function is independently documented by the UniProt FUNCTION record, and the IDA row is retained by deferral to the RGD curator (who read the full text). Supporting Evidence: UniProtKB:P00502 FUNCTION: Glutathione S-transferase that catalyzes the nucleophilic attack of the sulfur atom of glutathione on the electrophilic groups of a wide range of exogenous and endogenous compounds (Probable). PMID:17112229 In this work glutathione S-transferase (GST), a well-known and abundant BB-target protein, was isolated from liver cytosol of rats treated with 14C-BB by use of a glutathione (GSH)-agarose affinity column and further resolved by reverse-phase high-performance liquid chromatography (HPLC) into subunits M1, M2, A1, A2 and A3. |
| GO:0042803 protein homodimerization activity | IDA PMID:15152091 Heterodimers of wild-type and subunit interface mutant enzym... | KEEP AS NON CORE | Summary: protein homodimerization activity is retained as useful context for Gsta1, but it is not the defining core function (IDA, PMID:15152091). Reason: protein homodimerization activity records substrate, cofactor, or quaternary-structure context for Gsta1, but the curated core function is glutathione conjugation of electrophilic endogenous and xenobiotic substrates. Supporting Evidence: PMID:15152091 Heterodimers of rat glutathione S-transferase A1-1 were formed using one wild-type subunit and one subunit with a mutation at the interface to evaluate whether the subunits are interactive or independent. file:rat/Gsta1/Gsta1-deep-research-falcon.md Mammalian cytosolic GSTs are typically **homodimers** and have an N-terminal domain with a thioredoxin-like fold; they contain a **G-site** that binds GSH and a hydrophobic substrate-binding site. |
| GO:0043295 glutathione binding | IDA PMID:15152091 Heterodimers of wild-type and subunit interface mutant enzym... | KEEP AS NON CORE | Summary: glutathione binding is retained as useful context for Gsta1, but it is not the defining core function (IDA, PMID:15152091). Reason: glutathione binding records substrate, cofactor, or quaternary-structure context for Gsta1, but the curated core function is glutathione conjugation of electrophilic endogenous and xenobiotic substrates. Supporting Evidence: PMID:15152091 Heterodimers of rat glutathione S-transferase A1-1 were formed using one wild-type subunit and one subunit with a mutation at the interface to evaluate whether the subunits are interactive or independent. |
| GO:0043295 glutathione binding | IDA PMID:17112229 Site-specific arylation of rat glutathione s-transferase A1 ... | KEEP AS NON CORE | Summary: glutathione binding is retained as useful context for Gsta1, but it is not the defining core function (IDA, PMID:17112229). Reason: glutathione binding records substrate, cofactor, or quaternary-structure context for Gsta1, but the curated core function is glutathione conjugation of electrophilic endogenous and xenobiotic substrates. Supporting Evidence: PMID:17112229 In this work glutathione S-transferase (GST), a well-known and abundant BB-target protein, was isolated from liver cytosol of rats treated with 14C-BB by use of a glutathione (GSH)-agarose affinity column and further resolved by reverse-phase high-performance liquid chromatography (HPLC) into subunits M1, M2, A1, A2 and A3. |
| GO:0004364 glutathione transferase activity | IDA PMID:10751412 The catalytic Tyr-9 of glutathione S-transferase A1-1 contro... | ACCEPT | Summary: Gsta1's glutathione conjugation of electrophilic endogenous and xenobiotic substrates supports retaining glutathione transferase activity as a direct annotation (IDA, PMID:10751412). Reason: glutathione transferase activity is a specific catalytic activity matching Gsta1's documented role in glutathione conjugation of electrophilic endogenous and xenobiotic substrates. Supporting Evidence: PMID:10751412 The glutathione S-transferase enzymes (GSTs) have a tyrosine or serine residue at their active site that hydrogen bonds to and stabilizes the thiolate anion of glutathione, GS(-). |
| GO:0043295 glutathione binding | IDA PMID:10751412 The catalytic Tyr-9 of glutathione S-transferase A1-1 contro... | KEEP AS NON CORE | Summary: glutathione binding is retained as useful context for Gsta1, but it is not the defining core function (IDA, PMID:10751412). Reason: glutathione binding records substrate, cofactor, or quaternary-structure context for Gsta1, but the curated core function is glutathione conjugation of electrophilic endogenous and xenobiotic substrates. Supporting Evidence: PMID:10751412 The glutathione S-transferase enzymes (GSTs) have a tyrosine or serine residue at their active site that hydrogen bonds to and stabilizes the thiolate anion of glutathione, GS(-). PMID:10751412 Here, we demonstrate the effects of the Y9F substitution on binding affinity for glutathione conjugates and on rates of the order-disorder transition of the C terminus in rat GST A1-1. |
| GO:0030855 epithelial cell differentiation | ISO GO_REF:0000121 | MARK AS OVER ANNOTATED | Summary: epithelial cell differentiation is treated as over-annotation because it reflects context or consequence rather than Gsta1's direct role (ISO, GO_REF:0000121). Reason: epithelial cell differentiation reflects exposure, expression, phenotype, or downstream pathway context rather than the direct Gsta1 role in glutathione conjugation of electrophilic endogenous and xenobiotic substrates. Propagation Review Root cause: PROPAGATION BAD Failure modes: ROLE CONFLATION WRONG ORTHOLOG OR PARALOG Sources checked: UniProtKB:P09210 · human GSTA2 SUPPORTS SOURCE BUT NOT TARGET The donor is human GSTA2, not the GSTA1 counterpart of the target, so the transfer crosses alpha-class paralogues. More importantly the donor term captures differentiation-associated expression of an alpha-class GST in epithelium rather than a role for the enzyme in executing differentiation, so importing it recasts a detoxification enzyme as a differentiation effector. |
| GO:0035634 response to stilbenoid | ISO GO_REF:0000121 | MARK AS OVER ANNOTATED | Summary: response to stilbenoid is treated as over-annotation because it reflects context or consequence rather than Gsta1's direct role (ISO, GO_REF:0000121). Reason: response to stilbenoid reflects exposure, expression, phenotype, or downstream pathway context rather than the direct Gsta1 role in glutathione conjugation of electrophilic endogenous and xenobiotic substrates. Propagation Review Root cause: PROPAGATION BAD Failure modes: WRONG ORTHOLOG OR PARALOG SOURCE EVIDENCE WEAK Sources checked: MGI:MGI:95863 · mouse Gsta2 SUPPORTS SOURCE BUT NOT TARGET Transcriptional induction by a stilbenoid is legitimately what a "response to X" term denotes, so the donor annotation itself is not misconceived. The problem is the transfer: rodent alpha-class GST symbols are not 1:1 orthologous between mouse and rat, so the symbol-matched step from mouse Gsta2 to rat Gsta1 (P00502) crosses paralogues, and stilbenoid induction has not been demonstrated for rat Gsta1 itself. Alpha-class GSTs also differ markedly in inducer responsiveness, so induction of one family member is weak grounds for annotating another. |
| GO:0005829 cytosol | ISO GO_REF:0000121 | KEEP AS NON CORE | Summary: Cytosol transferred by orthology from human GSTA2 (UniProtKB:P09210); donor-split duplicate of the mouse-Gsta2-donor cytosol ISO row. Kept as non-core localization context, consistent with its sibling and with the rat IDA row. Reason: The donor is human GSTA2 (P09210), an alpha-class paralogue-level match rather than a clean one-to-one orthologue of rat Gsta1, but cytosolic location is shared by all alpha-class GSTs and is independently established for rat GSTA1, which was purified from rat liver cytosol (IDA, PMID:17112229) and is recorded by UniProt as cytoplasmic. The transfer is therefore correct in outcome; as a localization it does not define the core activity. Propagation Review Root cause: NO FAILURE NON CORE Sources checked: UniProtKB:P09210 · human GSTA2 SUPPORTS TRANSFER Human GSTA2 is cytosolic like every alpha-class GST; although the donor is not a strict one-to-one orthologue of rat Gsta1, the cytosolic location is confirmed for rat GSTA1 itself by direct assay, so the transferred claim holds for the target. Supporting Evidence: UniProtKB:P00502 SUBCELLULAR LOCATION: Cytoplasm. PMID:17112229 was isolated from liver cytosol of rats treated with 14C-BB |
| GO:0047066 phospholipid-hydroperoxide glutathione peroxidase activity | ISS GO_REF:0000024 | KEEP AS NON CORE | Summary: Phospholipid-hydroperoxide glutathione peroxidase activity transferred by sequence similarity from human GSTA1 (UniProtKB:P08263), matching the UniProt 13-HPODE peroxidase reaction curated for rat GSTA1 by similarity; kept as a genuine but secondary activity, consistent with the IEA row for the same term. Reason: The donor is human GSTA1 (P08263), whose selenium-independent glutathione peroxidase activity toward fatty-acid and phospholipid hydroperoxides is the basis of the UniProt rat reaction annotation. Alpha-class GSTs share this peroxidase activity, so the transfer is reasonable, but it has not been measured on purified rat GST A1-1 (see suggested_questions) and it is a side activity of the same glutathione-binding site rather than the defining conjugation function. The phospholipid-hydroperoxide half of the term (which the rat 13-HPODE reaction does not itself cover) is supported for the alpha class by the human ortholog hGSTA1-1, measured directly on PC- and PE-hydroperoxide (PMID:10395737). Propagation Review Root cause: NO FAILURE NON CORE Sources checked: UniProtKB:P08263 · human GSTA1 SUPPORTS TRANSFER Human GSTA1 has experimentally characterized glutathione peroxidase activity toward lipid hydroperoxides, a conserved alpha-class property of the shared active site; the transfer is plausible for rat GSTA1 though not yet measured on the rat enzyme. Supporting Evidence: PMID:10395737 catalytic efficiency (kcat/Km) of hGSTA1-1 for phosphatidylcholine (PC) hydroperoxide and phosphatidylethanolamine (PE) hydroperoxide was found to be 181.3 and 199.6 s-1 mM-1 UniProtKB:P00502 Through its glutathione-dependent peroxidase activity toward the fatty acid hydroperoxide (13S)-hydroperoxy-(9Z,11E)-octadecadienoate/13-HPODE it is also involved in the metabolism of oxidized linoleic acid (By similarity). file:rat/Gsta1/Gsta1-deep-research-falcon.md In mammalian systems, **A-class (alpha) GSTs** are noted for (i) high activity in detoxification pathways and (ii) **selenium-independent glutathione peroxidase (GPx)-like activity**, including reduction of lipid and sterol hydroperoxides in membranes. |
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Download this section (compressed HTML)Q: UniProt records prostaglandin A2/J2 conjugation, D5-androstene-3,17-dione isomerisation, and 13-HPODE peroxidase activity for rat GSTA1 largely by similarity to human GSTA1 (P08263). Which of these secondary activities have been measured directly on purified rat GST A1-1, and at what catalytic efficiency relative to the canonical CDNB-type conjugation?
Q: Rat Gsta1 (Ya-1) and Gsta2 (Ya-2) are near-identical Ya-type subunits that also form A1-2 heterodimers. Is there a substrate or hydroperoxide class handled specifically by the A1-1 homodimer, or is the pair functionally redundant in liver?
Q: Rodent alpha-class GST symbols are not 1:1 orthologous between rat and mouse, so mouse Gsta2 (MGI:MGI:95863) is not necessarily the counterpart of rat Gsta1. Which mouse gene is the true orthologue and should serve as the ISO donor, and should the current symbol-matched ISO transfers be retracted?
Q: How much of the hepatic ligandin (non-catalytic hydrophobic-ligand binding) capacity attributed to alpha-class GSTs is contributed by GSTA1 specifically, and is that binding physiologically important for bilirubin or steroid handling in vivo?
Experiment: Purify recombinant rat GST A1-1 and determine kcat/Km in parallel for CDNB conjugation, prostaglandin A2 and J2 conjugation, D5-androstene-3,17-dione isomerisation, and 13-HPODE reduction; then repeat with an active-site Tyr-to-Phe mutant to test whether all four activities depend on the same thiolate-stabilising residue.
Hypothesis: The steroid isomerase, prostaglandin-conjugating, and hydroperoxide-reducing activities currently annotated to rat GSTA1 by similarity are genuine but minor side activities of the same glutathione-binding site, not independent physiological functions.
Type: comparative enzyme kinetics with active-site mutagenesis
Experiment: Reconstitute rat A1-1, A2-2, and A1-2 dimers from recombinant subunits and profile each against a panel of electrophiles and lipid hydroperoxides, then compare the profiles against glutathione-conjugate output measured in liver cytosol from wild-type and Gsta1-knockdown rats.
Hypothesis: Rat GSTA1 and GSTA2 are not functionally redundant, and the A1-1 homodimer has a distinct electrophile and hydroperoxide preference from A2-2 and from the A1-2 heterodimer.
Type: reconstituted-dimer substrate profiling with in vivo cross-check
Experiment: Fractionate rat liver into cytosol, proteinase-K-shaved mitochondria, and nuclear envelope, and quantify GSTA1 by targeted proteomics using tryptic peptides that discriminate Ya-1 from Ya-2, so the compartment call is made on a paralog-resolved basis.
Hypothesis: Rat GSTA1 is confined to the cytosol and does not localise to the mitochondrial matrix, so the ISO-derived mitochondrion annotation reflects symbol-matched transfer rather than rat biology.
Type: subcellular fractionation with paralog-discriminating targeted proteomics
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