Branched-chain amino acid aminotransferase (BCAT, EC 2.6.1.42) of fission yeast, encoded by SPBC428.02c and homologous to mammalian ECA39/BCAT and S. cerevisiae BAT1/BAT2. It is a pyridoxal 5'-phosphate-dependent class-IV aminotransferase. It reversibly transfers the amino group of glutamate to 2-oxoisovalerate, (S)-3-methyl-2-oxopentanoate and 2-oxoisocaproate (4-methyl-2-oxopentanoate), forming valine, isoleucine and leucine; this is the last step of all three biosynthetic routes and the first step of their catabolism. It is the only BCAT of S. pombe and complements the branched-chain amino acid auxotrophy of an S. cerevisiae bat1 bat2 double mutant. It has an N-terminal mitochondrial transit peptide and is present in mitochondria, but a tagged version was also seen in the cytoplasm and nucleus. How one enzyme serves the mitochondrial Ile/Val trunk and the cytosolic end of the leucine branch is unresolved.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003824 catalytic activity | IEA GO_REF:0000002 | MODIFY | Summary: InterPro (aminotransferase class IV) mapping to root catalytic activity; true but uninformative. Reason: Replace with the specific BCAT activity, as for S. cerevisiae BAT1/BAT2. Proposed replacements: branched-chain-amino-acid:2-oxoglutarate transaminase activity Supporting Evidence: file:SCHPO/eca39/eca39-uniprot.txt Reaction=L-leucine + 2-oxoglutarate = 4-methyl-2-oxopentanoate + L- |
| GO:0004084 branched-chain-amino-acid:2-oxoglutarate transaminase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Combined IEA (ARBA, IPR005786/IPR033939, EC 2.6.1.42) for branched-chain-amino-acid:2-oxoglutarate transaminase activity; the parent of the three substrate-specific activities. Core MF. Supporting Evidence: file:SCHPO/eca39/eca39-uniprot.txt Reaction=L-leucine + 2-oxoglutarate = 4-methyl-2-oxopentanoate + L- PMID:35325114 BCAT catalyzes the transamination of the amino group of Glu to Leu, Ile, and Val stereoselectively, with cofactor pyridoxal 5′-phosphate (PLP) |
| GO:0005634 nucleus | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: UniProt subcellular-location mapping of the ORFeome YFP call (nucleus and cytoplasm). A soluble enzyme can equilibrate into the nucleus; no nuclear function is known. Reason: Not contradicted but without functional significance; non-core. Supporting Evidence: file:SCHPO/eca39/eca39-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion {ECO:0000305}. Nucleus file:SCHPO/eca39/eca39-uniprot.txt {ECO:0000269|PubMed:16823372}. Cytoplasm {ECO:0000269|PubMed:16823372}. |
| GO:0005737 cytoplasm | IEA GO_REF:0000120 | ACCEPT | Summary: ARBA/UniProt mapping to cytoplasm; supported by the ORFeome YFP signal and true under GO's definition of cytoplasm, which also covers the mitochondrial pool. Supporting Evidence: file:SCHPO/eca39/eca39-uniprot.txt {ECO:0000269|PubMed:16823372}. Cytoplasm {ECO:0000269|PubMed:16823372}. PMID:35325114 As in Anheuser-Busch baker's yeast, BCAT Eca39 has been confirmed to be present in various parts of S. pombe cells, including cytoplasm and mitochondria |
| GO:0005739 mitochondrion | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA (PTN000214536; donors include S. pombe eca39, S. cerevisiae BAT1, human BCAT2) for is_active_in mitochondrion. eca39 has an annotated N-terminal transit peptide (1-47) and is the sole BCAT completing the mitochondrial Ile/Val trunk. Supporting Evidence: PMID:35325114 As in Anheuser-Busch baker's yeast, BCAT Eca39 has been confirmed to be present in various parts of S. pombe cells, including cytoplasm and mitochondria file:SCHPO/eca39/eca39-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion {ECO:0000305}. Nucleus |
| GO:0005739 mitochondrion | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular-location mapping (Mitochondrion, curator inference from the transit peptide); consistent with the IBA. Supporting Evidence: file:SCHPO/eca39/eca39-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion {ECO:0000305}. Nucleus |
| GO:0005759 mitochondrial matrix | IGI PMID:9483807 Characterization of a branched-chain amino-acid aminotransfe... | ACCEPT | Summary: PomBase IGI for mitochondrial matrix from the complementation study (with BAT1). The abstract does not describe localisation, but the 2022 review cites Eden & Benvenisty for eca39 presence in mitochondria, and eca39 has a transit peptide. Defer to the curator. Supporting Evidence: PMID:35325114 As in Anheuser-Busch baker's yeast, BCAT Eca39 has been confirmed to be present in various parts of S. pombe cells, including cytoplasm and mitochondria file:SCHPO/eca39/eca39-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion {ECO:0000305}. Nucleus |
| GO:0005829 cytosol | IC GO_REF:0000111 | KEEP AS NON CORE | Summary: PomBase curator inference (from GO:0052654) that the leucine transamination occurs in the cytosol, where leu1 makes 2-oxoisocaproate; this is how the PomBase GO-CAM places the leucine-branch eca39 activity. The ORFeome YFP signal is cytoplasmic, but whether the single S. pombe BCAT is dual-targeted or 2-oxoisocaproate re-enters mitochondria has not been established. Reason: Plausible but unresolved compartment for the leucine step; kept, not core. Supporting Evidence: PMID:35325114 As in Anheuser-Busch baker's yeast, BCAT Eca39 has been confirmed to be present in various parts of S. pombe cells, including cytoplasm and mitochondria PMID:35325114 The intracellular localizations of the enzymes involved in BCAA biosynthesis suggest that in S. pombe Ile and Val biosynthesis is completed in the mitochondria, but Leu biosynthesis involves reactions in both the cytosol and the mitochondria file:SCHPO/eca39/eca39-uniprot.txt {ECO:0000269|PubMed:16823372}. Cytoplasm {ECO:0000269|PubMed:16823372}. |
| GO:0006550 L-isoleucine catabolic process | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: PAINT IBA (PTN000214535) for L-isoleucine catabolism, inherited from the bifunctional ancestral BCAT. As the only S. pombe BCAT, eca39 should catalyse the reversible first catabolic transamination too, but there is no S. pombe catabolic evidence. Reason: Plausible secondary role of a reversible enzyme; biosynthesis is the established role in S. pombe. Supporting Evidence: PMID:35325114 These reactions are reversible and not only act as the last steps in BCAA syntheses but also as the first steps in the BCAA catabolic pathways file:SCHPO/eca39/eca39-uniprot.txt FUNCTION: Catalyzes the first reaction in the catabolism of the |
| GO:0006574 L-valine catabolic process | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: PAINT IBA for L-valine catabolism from the same ancestral BCAT node; plausible for the single, reversible S. pombe BCAT but not studied. Reason: Secondary role; non-core. Supporting Evidence: PMID:35325114 These reactions are reversible and not only act as the last steps in BCAA syntheses but also as the first steps in the BCAA catabolic pathways |
| GO:0009081 branched-chain amino acid metabolic process | IEA GO_REF:0000002 | MODIFY | Summary: InterPro mapping to branched-chain amino acid metabolic process; correct but too general given the established biosynthetic role. Reason: Replace with branched-chain amino acid biosynthetic process (as for S. cerevisiae BAT1). Proposed replacements: branched-chain amino acid biosynthetic process Supporting Evidence: PMID:35325114 At this stage, Ile and Val are produced by BCAAs aminotransferase (BCAT), encoded by eca39+, from (S)-3-methyl-2-oxopentanoate and 3-methyl-2-oxobutanoate, respectively PMID:35325114 The final step in Leu biosynthesis, i.e. the transamination reaction, is catalyzed by BCAT Eca39, which is the same enzyme as in Ile and Val syntheses |
| GO:0009082 branched-chain amino acid biosynthetic process | IEA GO_REF:0000117 | ACCEPT | Summary: ARBA rule for branched-chain amino acid biosynthesis; correct, eca39 performs the final transamination for all three BCAAs. Supporting Evidence: PMID:35325114 At this stage, Ile and Val are produced by BCAAs aminotransferase (BCAT), encoded by eca39+, from (S)-3-methyl-2-oxopentanoate and 3-methyl-2-oxobutanoate, respectively PMID:35325114 The final step in Leu biosynthesis, i.e. the transamination reaction, is catalyzed by BCAT Eca39, which is the same enzyme as in Ile and Val syntheses |
| GO:0009098 L-leucine biosynthetic process | IGI PMID:9483807 Characterization of a branched-chain amino-acid aminotransfe... | ACCEPT | Summary: Complementation of the BCAA auxotrophy of the S. cerevisiae bat1 bat2 strain; eca39 performs the final transamination of leucine synthesis. Supporting Evidence: PMID:9483807 A genetic growth assay for BCAT activity was established using an S. cerevisiae strain disrupted in both BCAT isoenzymes. PMID:35325114 The final step in Leu biosynthesis, i.e. the transamination reaction, is catalyzed by BCAT Eca39, which is the same enzyme as in Ile and Val syntheses |
| GO:0009099 L-valine biosynthetic process | IGI PMID:9483807 Characterization of a branched-chain amino-acid aminotransfe... | ACCEPT | Summary: Complementation of bat1 bat2 BCAA auxotrophy; correct for valine synthesis. Supporting Evidence: PMID:9483807 A genetic growth assay for BCAT activity was established using an S. cerevisiae strain disrupted in both BCAT isoenzymes. PMID:35325114 At this stage, Ile and Val are produced by BCAAs aminotransferase (BCAT), encoded by eca39+, from (S)-3-methyl-2-oxopentanoate and 3-methyl-2-oxobutanoate, respectively |
| GO:0030170 pyridoxal phosphate binding | ISS GO_REF:0000024 | KEEP AS NON CORE | Summary: ISS from S. cerevisiae BAT1 for pyridoxal phosphate binding; class-IV aminotransferases use PLP as cofactor. Reason: Cofactor binding underlying catalysis; non-core. Supporting Evidence: file:SCHPO/eca39/eca39-uniprot.txt Name=pyridoxal 5'-phosphate; Xref=ChEBI:CHEBI:597326; PMID:35325114 BCAT catalyzes the transamination of the amino group of Glu to Leu, Ile, and Val stereoselectively, with cofactor pyridoxal 5′-phosphate (PLP) |
| GO:0052654 L-leucine:2-oxoglutarate transaminase activity | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA for L-leucine transaminase activity; donors include eca39 itself (IGI). Correct substrate-specific child of the BCAT activity. Supporting Evidence: file:SCHPO/eca39/eca39-uniprot.txt Reaction=L-leucine + 2-oxoglutarate = 4-methyl-2-oxopentanoate + L- PMID:9483807 Consequently, the activity of the S. pombe BCAT was demonstrated by genetic and biochemical means. |
| GO:0052654 L-leucine:2-oxoglutarate transaminase activity | IEA GO_REF:0000116 | ACCEPT | Summary: Rhea mapping (RHEA:18321, leucine transamination); UniProt records this reaction for eca39 with experimental evidence (PMID:9483807). Supporting Evidence: file:SCHPO/eca39/eca39-uniprot.txt Reaction=L-leucine + 2-oxoglutarate = 4-methyl-2-oxopentanoate + L- |
| GO:0052654 L-leucine:2-oxoglutarate transaminase activity | IGI PMID:9483807 Characterization of a branched-chain amino-acid aminotransfe... | ACCEPT | Summary: Eden & Benvenisty complemented an S. cerevisiae bat1 bat2 double disruptant (with BAT1, P38891) with eca39 and showed BCAT activity biochemically. Correct for leucine transamination. Supporting Evidence: PMID:9483807 A genetic growth assay for BCAT activity was established using an S. cerevisiae strain disrupted in both BCAT isoenzymes. PMID:9483807 Consequently, the activity of the S. pombe BCAT was demonstrated by genetic and biochemical means. |
| GO:0052655 L-valine:2-oxoglutarate transaminase activity | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA for L-valine transaminase activity; correct. Supporting Evidence: file:SCHPO/eca39/eca39-uniprot.txt Reaction=L-valine + 2-oxoglutarate = 3-methyl-2-oxobutanoate + L- PMID:9483807 Consequently, the activity of the S. pombe BCAT was demonstrated by genetic and biochemical means. |
| GO:0052655 L-valine:2-oxoglutarate transaminase activity | IEA GO_REF:0000116 | ACCEPT | Summary: Rhea mapping (RHEA:24813, valine transamination); correct. Supporting Evidence: file:SCHPO/eca39/eca39-uniprot.txt Reaction=L-valine + 2-oxoglutarate = 3-methyl-2-oxobutanoate + L- |
| GO:0052655 L-valine:2-oxoglutarate transaminase activity | IGI PMID:9483807 Characterization of a branched-chain amino-acid aminotransfe... | ACCEPT | Summary: Same complementation study; correct for valine transamination. Supporting Evidence: PMID:9483807 A genetic growth assay for BCAT activity was established using an S. cerevisiae strain disrupted in both BCAT isoenzymes. PMID:9483807 Consequently, the activity of the S. pombe BCAT was demonstrated by genetic and biochemical means. |
| GO:0052656 L-isoleucine:2-oxoglutarate transaminase activity | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA for L-isoleucine transaminase activity; correct. Supporting Evidence: file:SCHPO/eca39/eca39-uniprot.txt Reaction=L-isoleucine + 2-oxoglutarate = (S)-3-methyl-2-oxopentanoate + PMID:9483807 Consequently, the activity of the S. pombe BCAT was demonstrated by genetic and biochemical means. |
| GO:0052656 L-isoleucine:2-oxoglutarate transaminase activity | IEA GO_REF:0000116 | ACCEPT | Summary: Rhea mapping (RHEA:24801, isoleucine transamination); correct. Supporting Evidence: file:SCHPO/eca39/eca39-uniprot.txt Reaction=L-isoleucine + 2-oxoglutarate = (S)-3-methyl-2-oxopentanoate + |
| GO:0052656 L-isoleucine:2-oxoglutarate transaminase activity | IGI PMID:9483807 Characterization of a branched-chain amino-acid aminotransfe... | ACCEPT | Summary: Same complementation study; correct for isoleucine transamination. Supporting Evidence: PMID:9483807 A genetic growth assay for BCAT activity was established using an S. cerevisiae strain disrupted in both BCAT isoenzymes. PMID:9483807 Consequently, the activity of the S. pombe BCAT was demonstrated by genetic and biochemical means. |
| GO:1901705 L-isoleucine biosynthetic process | IGI PMID:9483807 Characterization of a branched-chain amino-acid aminotransfe... | ACCEPT | Summary: Complementation of bat1 bat2 BCAA auxotrophy; correct for isoleucine synthesis. Supporting Evidence: PMID:9483807 A genetic growth assay for BCAT activity was established using an S. cerevisiae strain disrupted in both BCAT isoenzymes. PMID:35325114 At this stage, Ile and Val are produced by BCAAs aminotransferase (BCAT), encoded by eca39+, from (S)-3-methyl-2-oxopentanoate and 3-methyl-2-oxobutanoate, respectively |
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Download this section (compressed HTML)Experiment: Tag eca39 at the endogenous locus (C-terminal) and image with a mitochondrial marker; express transit-peptide-deleted and import-only variants in an eca39 deletion and test which restores growth without leucine, isoleucine or valine.
What is not known — curated, literature-grounded statements of the open unknowns (the inverse of core functions).
Gap: eca39 is the only S. pombe BCAT, yet the isoleucine/valine 2-oxoacids are made in mitochondria while 2-oxoisocaproate is made in the cytosol. Whether eca39 is dual-localised (for example by alternative translation start or partial import), or whether one compartment's 2-oxoacids are transported to the other, is unknown.
OPEN BIOLOGY
What is known: Established: transit peptide, mitochondrial presence, and a cytoplasmic/nuclear YFP signal from a C-terminally tagged ORFeome clone (possibly built on an earlier gene model; UniProt records a gene-model revision). Unknown: the endogenous distribution and the compartment in which each transamination occurs.
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