id: O15382
gene_symbol: BCAT2
product_type: PROTEIN
status: INITIALIZED
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: >-
  BCAT2 (BCAT(m)) is the mitochondrial branched-chain-amino-acid aminotransferase, a
  class-IV pyridoxal 5'-phosphate (PLP)-dependent enzyme (EC 2.6.1.42) that catalyzes the
  first, reversible step of branched-chain amino acid (BCAA) catabolism. It transaminates
  L-leucine, L-isoleucine and L-valine with 2-oxoglutarate (alpha-ketoglutarate) to yield
  the corresponding branched-chain 2-oxo (keto) acids (4-methyl-2-oxopentanoate/KIC,
  (S)-3-methyl-2-oxopentanoate/KMV and 3-methyl-2-oxobutanoate/KIV) plus L-glutamate. The
  branched-chain keto acids are then passed to the mitochondrial branched-chain ketoacid
  dehydrogenase (BCKDH) complex for irreversible oxidative decarboxylation. The enzyme
  functions as a PLP-bound homodimer in the mitochondrial matrix, with the PLP cofactor
  forming a Schiff base (internal aldimine) to an active-site lysine (Lys-229), and carries
  a redox-active CXXC center (Cys-342/Cys-345) near the active site that couples catalysis
  to thiol redox state. BCAT2 is broadly expressed with highest activity in extrahepatic
  tissues such as skeletal muscle; the paralog BCAT1 is the cytosolic isozyme. Because
  BCAAs are essential amino acids in humans, the physiological direction of the reaction is
  catabolic (nitrogen removal), and loss of BCAT2 function causes an autosomal-recessive
  inborn error of metabolism (hypervalinemia and hyperleucine-isoleucinemia) with elevated
  plasma BCAAs.
alternative_products:
- name: A
  id: O15382-1
- name: B
  id: O15382-2
  sequence_note: VSP_000236
existing_annotations:
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: is_active_in
  review:
    summary: >-
      Phylogenetic (PAN-GO) inference that BCAT2 is active in the mitochondrion. Consistent
      with the cleaved N-terminal mitochondrial transit peptide (residues 1-27) and with all
      experimental localization evidence.
    action: ACCEPT
    reason: >-
      BCAT2 has a 27-residue mitochondrial targeting presequence and is well established as a
      mitochondrial-matrix enzyme; the IBA is correct. Mitochondrial matrix (GO:0005759) is
      the more specific location captured elsewhere in the annotation set.
    supported_by:
    - reference_id: PMID:9165094
      supporting_text: >-
        encode mature proteins of 41.2 and 41.3 kDa with presequences of 27 amino acids
- term:
    id: GO:0006550
    label: L-isoleucine catabolic process
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: >-
      Phylogenetic inference that BCAT2 is involved in L-isoleucine catabolism. BCAT2
      transaminates isoleucine as the committed first step of its catabolism.
    action: ACCEPT
    reason: >-
      Isoleucine transamination is a core BCAT2 activity (GO:0052656), and the enzyme
      initiates isoleucine catabolism. Direct process annotation is appropriate and core.
    supported_by:
    - reference_id: PMID:8702755
      supporting_text: >-
        Activity of branched-chain amino acid aminotransferase was measured in the wild-type
        and mutants with either leucine, isoleucine, or valine as substrates
- term:
    id: GO:0006574
    label: L-valine catabolic process
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: >-
      Phylogenetic inference that BCAT2 is involved in L-valine catabolism, initiating valine
      breakdown by transamination to 3-methyl-2-oxobutanoate.
    action: ACCEPT
    reason: >-
      Valine transamination (GO:0052655) is a core BCAT2 activity; the enzyme initiates valine
      catabolism. Valine is the most conspicuously elevated BCAA in BCAT2 deficiency, underscoring
      its physiological role here.
    supported_by:
    - reference_id: PMID:8702755
      supporting_text: >-
        Activity of branched-chain amino acid aminotransferase was measured in the wild-type
        and mutants with either leucine, isoleucine, or valine as substrates
- term:
    id: GO:0052654
    label: L-leucine:2-oxoglutarate transaminase activity
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: enables
  review:
    summary: >-
      Phylogenetic inference of L-leucine:2-oxoglutarate transaminase activity, one of the three
      substrate-specific BCAT activities. Corroborated by IDA (PMID:8702755) and Rhea IEA.
    action: ACCEPT
    reason: >-
      This substrate-specific molecular function is directly demonstrated for BCAT2 and is one
      of its core enzymatic activities.
    supported_by:
    - reference_id: PMID:8702755
      supporting_text: >-
        code for cytosolic and mitochondrial branched-chain amino acid aminotransferases
- term:
    id: GO:0052655
    label: L-valine:2-oxoglutarate transaminase activity
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: enables
  review:
    summary: >-
      Phylogenetic inference of L-valine:2-oxoglutarate transaminase activity. Corroborated by IDA
      (PMID:8702755) and Rhea IEA (RHEA:24813).
    action: ACCEPT
    reason: >-
      Core substrate-specific transaminase activity of BCAT2, directly measured with valine as
      substrate.
    supported_by:
    - reference_id: PMID:8702755
      supporting_text: >-
        Activity of branched-chain amino acid aminotransferase was measured in the wild-type
        and mutants with either leucine, isoleucine, or valine as substrates
- term:
    id: GO:0052656
    label: L-isoleucine:2-oxoglutarate transaminase activity
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: enables
  review:
    summary: >-
      Phylogenetic inference of L-isoleucine:2-oxoglutarate transaminase activity. Corroborated by
      IDA (PMID:8702755) and Rhea IEA (RHEA:24801).
    action: ACCEPT
    reason: >-
      Core substrate-specific transaminase activity of BCAT2, directly measured with isoleucine as
      substrate.
    supported_by:
    - reference_id: PMID:8702755
      supporting_text: >-
        Activity of branched-chain amino acid aminotransferase was measured in the wild-type
        and mutants with either leucine, isoleucine, or valine as substrates
- term:
    id: GO:0003824
    label: catalytic activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: >-
      InterPro2GO mapping to the root catalytic-activity term. Correct but uninformative: BCAT2 is
      a specific PLP-dependent transaminase.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      GO:0003824 is a very general parent of the specific branched-chain aminotransferase activity
      (GO:0004084) and substrate-specific transaminase terms already annotated. It conveys no
      information beyond "is an enzyme" and is subsumed by the more precise MF annotations.
- term:
    id: GO:0004084
    label: branched-chain-amino-acid:2-oxoglutarate transaminase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: enables
  review:
    summary: >-
      Combined multi-method IEA (ARBA + orthology + InterPro + EC:2.6.1.42) assigning the general
      branched-chain aminotransferase molecular function. This is the correct core EC-level activity.
    action: ACCEPT
    reason: >-
      GO:0004084 is the primary molecular function of BCAT2 (EC 2.6.1.42) and is independently
      supported by direct experimental evidence (IDA PMID:8702755) and TAS (PMID:9165094).
    supported_by:
    - reference_id: PMID:8702755
      supporting_text: >-
        code for cytosolic and mitochondrial branched-chain amino acid aminotransferases
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: located_in
  review:
    summary: >-
      IEA localization to mitochondrion (orthology to mouse O35855 plus UniProt SubCell SL-0173).
      Consistent with all other localization evidence.
    action: ACCEPT
    reason: >-
      Mitochondrial localization is firmly established; matrix is the specific compartment.
    supported_by:
    - reference_id: PMID:9165094
      supporting_text: >-
        encode mature proteins of 41.2 and 41.3 kDa with presequences of 27 amino acids
- term:
    id: GO:0009081
    label: branched-chain amino acid metabolic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: involved_in
  review:
    summary: >-
      InterPro2GO mapping to the general BCAA metabolic process. Correct but a broad parent of the
      specific catabolic-process annotations.
    action: KEEP_AS_NON_CORE
    reason: >-
      GO:0009081 (BCAA metabolic process) is a correct but general parent of the more specific and
      physiologically directional BCAA catabolic process (GO:0009083) and the amino-acid-specific
      catabolic terms already annotated. Keep as non-core; the catabolic terms carry the core signal.
- term:
    id: GO:0009082
    label: branched-chain amino acid biosynthetic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  qualifier: involved_in
  review:
    summary: >-
      ARBA machine-learning IEA (and an older TAS) annotating branched-chain amino acid BIOSYNTHETIC
      process. The BCAT reaction is chemically reversible, but in humans BCAAs are essential and are
      not synthesized de novo; the physiological direction is catabolic.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      The reversible transamination can in principle re-aminate branched-chain keto acids, but net
      de novo BCAA biosynthesis is a bacterial/plant/fungal role of BCAT-family enzymes (e.g. IlvE),
      not the human physiological function. The biosynthetic-process annotation is transferred from
      the family/EC and over-states the in vivo role; the catabolic annotations are correct and core.
      (Retained as an over-annotation rather than removed, since the underlying reversible chemistry
      is real.)
    supported_by:
    - reference_id: PMID:8702755
      supporting_text: >-
        Activity of branched-chain amino acid aminotransferase was measured in the wild-type
        and mutants with either leucine, isoleucine, or valine as substrates
- term:
    id: GO:0009083
    label: branched-chain amino acid catabolic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  qualifier: involved_in
  review:
    summary: >-
      ARBA IEA to branched-chain amino acid catabolic process. This is the correct core biological
      process for BCAT2 and is independently supported by direct experimental evidence (IDA on the
      same term, PMID:8702755).
    action: ACCEPT
    reason: >-
      BCAT2 catalyzes the committed first step of BCAA catabolism; this is its central physiological
      role.
    supported_by:
    - reference_id: PMID:8702755
      supporting_text: >-
        code for cytosolic and mitochondrial branched-chain amino acid aminotransferases
    - reference_id: file:human/BCAT2/BCAT2-deep-research-falcon.md
      supporting_text: >-
        BCAT2 catalyzes the first step in mitochondrial BCAA catabolism
- term:
    id: GO:0052654
    label: L-leucine:2-oxoglutarate transaminase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000116
  qualifier: enables
  review:
    summary: >-
      Rhea-based IEA (RHEA:18321) for L-leucine:2-oxoglutarate transaminase activity. Matches the
      UniProt CATALYTIC ACTIVITY reaction for leucine.
    action: ACCEPT
    reason: >-
      Directly corresponds to a UniProt-documented catalytic reaction of BCAT2 and duplicates the
      experimentally supported (IDA/IBA) substrate-specific MF; correct and core.
    supported_by:
    - reference_id: PMID:8702755
      supporting_text: >-
        code for cytosolic and mitochondrial branched-chain amino acid aminotransferases
- term:
    id: GO:0052655
    label: L-valine:2-oxoglutarate transaminase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000116
  qualifier: enables
  review:
    summary: >-
      Rhea-based IEA (RHEA:24813) for L-valine:2-oxoglutarate transaminase activity, matching the
      UniProt CATALYTIC ACTIVITY reaction for valine.
    action: ACCEPT
    reason: >-
      Directly corresponds to a UniProt-documented catalytic reaction of BCAT2; core substrate-specific
      activity.
    supported_by:
    - reference_id: PMID:8702755
      supporting_text: >-
        Activity of branched-chain amino acid aminotransferase was measured in the wild-type
        and mutants with either leucine, isoleucine, or valine as substrates
- term:
    id: GO:0052656
    label: L-isoleucine:2-oxoglutarate transaminase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000116
  qualifier: enables
  review:
    summary: >-
      Rhea-based IEA (RHEA:24801) for L-isoleucine:2-oxoglutarate transaminase activity, matching the
      UniProt CATALYTIC ACTIVITY reaction for isoleucine.
    action: ACCEPT
    reason: >-
      Directly corresponds to a UniProt-documented catalytic reaction of BCAT2; core substrate-specific
      activity.
    supported_by:
    - reference_id: PMID:8702755
      supporting_text: >-
        Activity of branched-chain amino acid aminotransferase was measured in the wild-type
        and mutants with either leucine, isoleucine, or valine as substrates
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:28514442
  qualifier: enables
  review:
    summary: >-
      Interaction detected in the BioPlex 2.0 high-throughput AP-MS interactome screen (interactors
      include HSPD1/P10809 and YBEY/P58557). "Protein binding" is uninformative about BCAT2's molecular
      function.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      GO:0005515 "protein binding" from a proteome-scale AP-MS screen conveys no specific functional
      information and is discouraged for core-function purposes. Per curation policy the experimental
      IPI is retained rather than removed, but it is marked as an over-annotation. (The
      BCAT2-HSPD1/HSP60 co-purification plausibly reflects mitochondrial chaperone association rather
      than a discrete functional partnership.)
    supported_by:
    - reference_id: PMID:28514442
      supporting_text: >-
        robust affinity purification-mass spectrometry methodology to elucidate protein
        interaction networks and co-complexes
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:29568061
  qualifier: enables
  review:
    summary: >-
      Interaction (with HSPD1/P10809) detected using the MAC-tag AP-MS/BioID proximity-labeling
      platform. Bare "protein binding" from a high-throughput mapping method.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      High-throughput proximity/AP-MS "protein binding" is uninformative for BCAT2 core function.
      Retained as an experimental IPI per policy but marked as over-annotation; the HSPD1/HSP60
      association is consistent with the mitochondrial matrix chaperone environment rather than a
      specific functional interaction.
    supported_by:
    - reference_id: PMID:29568061
      supporting_text: >-
        comprehensive mapping of protein interactions and subcellular localizations
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:33961781
  qualifier: enables
  review:
    summary: >-
      Interactions (HSPD1/P10809, YBEY/P58557) from the BioPlex 3.0 dual proteome-scale AP-MS
      interactome. Bare "protein binding" from a high-throughput screen.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Proteome-scale AP-MS "protein binding" is uninformative about BCAT2's molecular function.
      Retained as an experimental IPI per policy, marked as over-annotation.
    supported_by:
    - reference_id: PMID:33961781
      supporting_text: >-
        cell-specific remodeling of the human interactome
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:40205054
  qualifier: enables
  review:
    summary: >-
      Interactions (HSPD1/P10809, YBEY/P58557) from a multimodal cell-map interactome dataset. Bare
      "protein binding" from a high-throughput mapping study.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      High-throughput interactome "protein binding" is uninformative for BCAT2 core function.
      Retained as an experimental IPI per policy, marked as over-annotation.
    supported_by:
    - reference_id: PMID:40205054
      supporting_text: >-
        Multimodal cell maps as a foundation for structural and functional genomics
- term:
    id: GO:0005759
    label: mitochondrial matrix
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: is_active_in
  review:
    summary: >-
      Ensembl-Compara orthology IEA (from mouse) placing BCAT2 activity in the mitochondrial matrix,
      the specific compartment where BCAA transamination occurs.
    action: ACCEPT
    reason: >-
      Mitochondrial matrix is the correct, specific subcellular location for this soluble matrix
      enzyme, consistent with its cleaved transit peptide and TAS/Reactome annotations.
    supported_by:
    - reference_id: PMID:9165094
      supporting_text: >-
        encode mature proteins of 41.2 and 41.3 kDa with presequences of 27 amino acids
- term:
    id: GO:0006552
    label: L-leucine catabolic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara orthology IEA (from mouse) for L-leucine catabolic process. BCAT2 initiates
      leucine catabolism by transamination to 4-methyl-2-oxopentanoate (KIC).
    action: ACCEPT
    reason: >-
      Leucine transamination (GO:0052654) is a core BCAT2 activity and the enzyme initiates leucine
      catabolism; the process annotation is appropriate and core.
    supported_by:
    - reference_id: PMID:8702755
      supporting_text: >-
        Activity of branched-chain amino acid aminotransferase was measured in the wild-type
        and mutants with either leucine, isoleucine, or valine as substrates
- term:
    id: GO:0006574
    label: L-valine catabolic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara orthology IEA (from mouse) for L-valine catabolic process. Duplicates the IBA
      valine-catabolism annotation; correct and core.
    action: ACCEPT
    reason: >-
      BCAT2 initiates valine catabolism; core biological process.
    supported_by:
    - reference_id: PMID:8702755
      supporting_text: >-
        Activity of branched-chain amino acid aminotransferase was measured in the wild-type
        and mutants with either leucine, isoleucine, or valine as substrates
- term:
    id: GO:0097009
    label: energy homeostasis
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Ensembl-Compara orthology IEA (from mouse) for energy homeostasis. BCAA catabolism feeds
      acetyl-CoA/succinyl-CoA into the TCA cycle and BCAT2 loss alters energy expenditure in mice,
      but this is a broad downstream physiological consequence rather than the enzyme's molecular role.
    action: KEEP_AS_NON_CORE
    reason: >-
      Energy homeostasis is a general, pleiotropic downstream process to which BCAA catabolism
      contributes indirectly (e.g. BCAT2-knockout mice show increased energy expenditure). It is not
      the core enzymatic function; keep as non-core.
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: IDA
  original_reference_id: GO_REF:0000052
  qualifier: located_in
  review:
    summary: >-
      Direct immunofluorescence localization (Human Protein Atlas) placing BCAT2 in the mitochondrion.
    action: ACCEPT
    reason: >-
      Experimental (IDA) immunofluorescence confirms mitochondrial localization, in agreement with
      all other evidence; matrix is the specific compartment.
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: ISS
  original_reference_id: GO_REF:0000024
  qualifier: located_in
  review:
    summary: >-
      Sequence-similarity localization to mitochondrion, transferred from rat ortholog (O35854).
      Consistent with the transit peptide and experimental data.
    action: ACCEPT
    reason: >-
      Mitochondrial localization is firmly established across evidence types.
    supported_by:
    - reference_id: PMID:9165094
      supporting_text: >-
        encode mature proteins of 41.2 and 41.3 kDa with presequences of 27 amino acids
- term:
    id: GO:0009083
    label: branched-chain amino acid catabolic process
  evidence_type: IDA
  original_reference_id: PMID:8702755
  qualifier: involved_in
  review:
    summary: >-
      Direct experimental evidence that BCAT2 participates in BCAA catabolism: BCAT activity toward
      leucine, isoleucine and valine was measured, and the human/yeast homologs encode the
      branched-chain aminotransferases initiating BCAA breakdown.
    action: ACCEPT
    reason: >-
      This is the core biological process of BCAT2, supported by direct enzymatic assays with all
      three BCAA substrates.
    supported_by:
    - reference_id: PMID:8702755
      supporting_text: >-
        Activity of branched-chain amino acid aminotransferase was measured in the wild-type
        and mutants with either leucine, isoleucine, or valine as substrates
- term:
    id: GO:0050873
    label: brown fat cell differentiation
  evidence_type: ISS
  original_reference_id: GO_REF:0000024
  qualifier: acts_upstream_of_negative_effect
  review:
    summary: >-
      Sequence-similarity annotation transferred from mouse (O35855): BCAA catabolism supplies
      lipogenic acetyl-CoA that EP300/p300 uses to acetylate and inhibit PRDM16, preventing adipose
      browning. A real but indirect metabolic-signalling role, downstream of the catabolic function.
    action: KEEP_AS_NON_CORE
    reason: >-
      This links BCAT2 to a specific downstream developmental/metabolic output (brown fat
      differentiation) via acetyl-CoA supply and PRDM16 regulation. It is genuine (documented in
      mouse orthologs) but is a peripheral, indirect role rather than BCAT2's core enzymatic function;
      keep as non-core.
    supported_by:
    - reference_id: UniProtKB:O35855
      supporting_text: >-
        acetyl-CoA derived from branched chain amino acid catabolism is used by EP300/p300 to
        acetylate and inhibit PRDM16, thereby preventing adipose tissue browning
    additional_reference_ids:
    - UniProtKB:O35855
- term:
    id: GO:0004084
    label: branched-chain-amino-acid:2-oxoglutarate transaminase activity
  evidence_type: IDA
  original_reference_id: PMID:8702755
  qualifier: enables
  review:
    summary: >-
      Direct experimental demonstration of branched-chain aminotransferase activity for the cloned
      mitochondrial enzyme, assayed with leucine, isoleucine and valine as substrates.
    action: ACCEPT
    reason: >-
      This is the core molecular function of BCAT2 (EC 2.6.1.42), established by direct enzymatic
      assay.
    supported_by:
    - reference_id: PMID:8702755
      supporting_text: >-
        Activity of branched-chain amino acid aminotransferase was measured in the wild-type
        and mutants with either leucine, isoleucine, or valine as substrates
- term:
    id: GO:1903444
    label: negative regulation of brown fat cell differentiation
  evidence_type: ISS
  original_reference_id: GO_REF:0000024
  qualifier: involved_in
  review:
    summary: >-
      Sequence-similarity annotation transferred from mouse (MGI:1276534) for negative regulation of
      brown fat cell differentiation, via BCAA-catabolism-derived acetyl-CoA and EP300/PRDM16
      signalling.
    action: KEEP_AS_NON_CORE
    reason: >-
      Same indirect brown-fat/PRDM16 axis as GO:0050873; a genuine downstream metabolic-signalling
      role documented in mouse but peripheral to BCAT2's core transaminase function. Keep as non-core.
    supported_by:
    - reference_id: UniProtKB:O35855
      supporting_text: >-
        acetyl-CoA derived from branched chain amino acid catabolism is used by EP300/p300 to
        acetylate and inhibit PRDM16, thereby preventing adipose tissue browning
    additional_reference_ids:
    - UniProtKB:O35855
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: HTP
  original_reference_id: PMID:34800366
  qualifier: located_in
  review:
    summary: >-
      High-throughput proteomic assignment of BCAT2 to the high-confidence human mitochondrial
      proteome (MitoCoP).
    action: ACCEPT
    reason: >-
      Corroborates mitochondrial localization by an orthogonal high-throughput proteomics method,
      consistent with all other evidence.
    supported_by:
    - reference_id: PMID:34800366
      supporting_text: >-
        defined a mitochondrial high-confidence proteome of >1,100 proteins (MitoCoP)
- term:
    id: GO:0052654
    label: L-leucine:2-oxoglutarate transaminase activity
  evidence_type: IDA
  original_reference_id: PMID:8702755
  qualifier: enables
  review:
    summary: >-
      Direct experimental demonstration of L-leucine transaminase activity for the mitochondrial
      branched-chain aminotransferase.
    action: ACCEPT
    reason: >-
      Core substrate-specific molecular function, directly measured with leucine as substrate.
    supported_by:
    - reference_id: PMID:8702755
      supporting_text: >-
        Activity of branched-chain amino acid aminotransferase was measured in the wild-type
        and mutants with either leucine, isoleucine, or valine as substrates
- term:
    id: GO:0052655
    label: L-valine:2-oxoglutarate transaminase activity
  evidence_type: IDA
  original_reference_id: PMID:8702755
  qualifier: enables
  review:
    summary: >-
      Direct experimental demonstration of L-valine transaminase activity for the mitochondrial
      branched-chain aminotransferase.
    action: ACCEPT
    reason: >-
      Core substrate-specific molecular function, directly measured with valine as substrate.
    supported_by:
    - reference_id: PMID:8702755
      supporting_text: >-
        Activity of branched-chain amino acid aminotransferase was measured in the wild-type
        and mutants with either leucine, isoleucine, or valine as substrates
- term:
    id: GO:0052656
    label: L-isoleucine:2-oxoglutarate transaminase activity
  evidence_type: IDA
  original_reference_id: PMID:8702755
  qualifier: enables
  review:
    summary: >-
      Direct experimental demonstration of L-isoleucine transaminase activity for the mitochondrial
      branched-chain aminotransferase.
    action: ACCEPT
    reason: >-
      Core substrate-specific molecular function, directly measured with isoleucine as substrate.
    supported_by:
    - reference_id: PMID:8702755
      supporting_text: >-
        Activity of branched-chain amino acid aminotransferase was measured in the wild-type
        and mutants with either leucine, isoleucine, or valine as substrates
- term:
    id: GO:0005759
    label: mitochondrial matrix
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-508179
  qualifier: located_in
  review:
    summary: >-
      Reactome traceable-author-statement placing the BCAT2 reaction in the mitochondrial matrix
      (reverse direction: keto acids + glutamate to BCAAs + alpha-ketoglutarate).
    action: ACCEPT
    reason: >-
      Mitochondrial matrix is the correct specific location for this enzyme; Reactome annotation is
      consistent with all other evidence.
- term:
    id: GO:0005759
    label: mitochondrial matrix
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-70724
  qualifier: located_in
  review:
    summary: >-
      Reactome traceable-author-statement placing the BCAT2 reaction in the mitochondrial matrix
      (forward catabolic direction: BCAAs + alpha-ketoglutarate to keto acids + glutamate).
    action: ACCEPT
    reason: >-
      Mitochondrial matrix is the correct specific location for this enzyme; consistent with all
      other evidence.
- term:
    id: GO:0004084
    label: branched-chain-amino-acid:2-oxoglutarate transaminase activity
  evidence_type: TAS
  original_reference_id: PMID:9165094
  qualifier: enables
  review:
    summary: >-
      Traceable author statement (cloning of rat and human BCATm) supporting the branched-chain
      aminotransferase molecular function. This paper established the BCAT1/BCAT2 nomenclature and
      showed the cloned enzyme has BCAT activity.
    action: ACCEPT
    reason: >-
      Corroborates the core EC-level molecular function of BCAT2 with TAS from the defining cloning
      paper.
    supported_by:
    - reference_id: PMID:9165094
      supporting_text: >-
        the protein exhibits BCAT activity and correct processing of the mitochondrial targeting
        sequence
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: TAS
  original_reference_id: PMID:9165094
  qualifier: located_in
  review:
    summary: >-
      Traceable author statement for mitochondrial localization from the BCATm cloning paper, which
      demonstrated correct processing of the mitochondrial targeting presequence.
    action: ACCEPT
    reason: >-
      Mitochondrial localization is established; the cloning paper showed proper mitochondrial
      targeting-sequence processing.
    supported_by:
    - reference_id: PMID:9165094
      supporting_text: >-
        the protein exhibits BCAT activity and correct processing of the mitochondrial targeting
        sequence
- term:
    id: GO:0009082
    label: branched-chain amino acid biosynthetic process
  evidence_type: TAS
  original_reference_id: PMID:8702755
  qualifier: involved_in
  review:
    summary: >-
      Older TAS annotating branched-chain amino acid BIOSYNTHETIC process, presumably reflecting the
      chemically reversible transamination. In humans BCAAs are essential and not synthesized de novo,
      so the physiological direction is catabolic.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      The reversible reaction can re-aminate branched-chain keto acids, but net BCAA biosynthesis is a
      microbial/plant role of BCAT-family enzymes, not the human function; humans require dietary BCAAs.
      The biosynthetic-process annotation over-states the in vivo role. Retained as an over-annotation
      (the reversible chemistry is real) rather than removed.
    supported_by:
    - reference_id: PMID:8702755
      supporting_text: >-
        code for cytosolic and mitochondrial branched-chain amino acid aminotransferases
- term:
    id: GO:0030170
    label: pyridoxal phosphate binding
  evidence_type: IDA
  original_reference_id: PMID:8702755
  qualifier: enables
  review:
    summary: >-
      Proposed annotation (not in current GOA): BCAT2 binds pyridoxal 5'-phosphate (PLP) as its
      essential catalytic cofactor. UniProt records PLP as the cofactor (COFACTOR, from crystallographic
      studies) and a Schiff-base MOD_RES at Lys-229; PLP binding is required for the demonstrated
      aminotransferase activity.
    action: NEW
    reason: >-
      PLP-binding is a well-established, structurally and biochemically documented molecular function of
      this class-IV PLP-dependent aminotransferase (many BCATm crystal structures resolve the PLP
      cofactor; the Schiff-base lysine is annotated in UniProt) and directly underlies its catalytic
      activity. It is currently missing from GOA and is added here as a core function.
    supported_by:
    - reference_id: file:human/BCAT2/BCAT2-uniprot.txt
      supporting_text: "Name=pyridoxal 5'-phosphate; Xref=ChEBI:CHEBI:597326;"
core_functions:
- description: >-
    BCAT2 is the mitochondrial branched-chain-amino-acid aminotransferase (EC 2.6.1.42) that
    catalyzes the first, reversible step of branched-chain amino acid catabolism: PLP-dependent
    transamination of L-leucine, L-isoleucine and L-valine with 2-oxoglutarate to give the
    corresponding branched-chain 2-oxo acids (KIC, KMV, KIV) plus L-glutamate, feeding the products
    to the mitochondrial BCKDH complex. It acts as a homodimer in the mitochondrial matrix.
  molecular_function:
    id: GO:0004084
    label: branched-chain-amino-acid:2-oxoglutarate transaminase activity
  directly_involved_in:
  - id: GO:0009083
    label: branched-chain amino acid catabolic process
  locations:
  - id: GO:0005759
    label: mitochondrial matrix
  substrates:
  - id: CHEBI:15603
    label: L-leucine
  - id: CHEBI:17191
    label: L-isoleucine
  - id: CHEBI:16414
    label: L-valine
  - id: CHEBI:16810
    label: 2-oxoglutarate
  supported_by:
  - reference_id: PMID:8702755
    supporting_text: >-
      Activity of branched-chain amino acid aminotransferase was measured in the wild-type
      and mutants with either leucine, isoleucine, or valine as substrates
  - reference_id: PMID:9165094
    supporting_text: >-
      the protein exhibits BCAT activity and correct processing of the mitochondrial targeting
      sequence
- description: >-
    Catalysis requires the cofactor pyridoxal 5'-phosphate (PLP), which is bound at the active site
    via a Schiff-base (internal aldimine) linkage to Lys-229 and cycles between the aldimine (PLP)
    and pyridoxamine (PMP) forms during the ping-pong transamination mechanism. PLP binding is
    essential for BCAT2 aminotransferase activity, and the disease-relevant loss of activity can be
    partially rescued by vitamin B6 (PLP precursor) supplementation.
  molecular_function:
    id: GO:0030170
    label: pyridoxal phosphate binding
  directly_involved_in:
  - id: GO:0009083
    label: branched-chain amino acid catabolic process
  locations:
  - id: GO:0005759
    label: mitochondrial matrix
proposed_new_terms: []
suggested_questions:
- question: >-
    In human tissues, does BCAT2 carry any physiologically relevant biosynthetic (re-amination)
    flux toward BCAAs, or is the net direction exclusively catabolic given the essentiality of
    dietary BCAAs?
- question: >-
    To what extent do the reported BCAT2 protein-protein interactions (e.g. with HSPD1/HSP60) and
    the CXXC-dependent metabolon with the BCKDH E1 subunit represent discrete functional partnerships
    versus co-purification within the mitochondrial matrix?
suggested_experiments:
- description: >-
    Quantify BCAA-to-BCKA flux directionality in situ (e.g. stable-isotope 15N/13C tracing) in
    BCAT2-expressing human muscle vs liver models to determine whether any net biosynthetic
    re-amination occurs physiologically.
- description: >-
    Reconstitute the BCAT2-BCKDH E1 metabolon in vitro with reduced vs oxidized CXXC-center BCAT2
    (and C342A/C345A mutants) to test how the redox state of the CXXC center gates substrate
    channeling and overall BCAA oxidation rate.
references:
- id: file:human/BCAT2/BCAT2-deep-research-falcon.md
  title: Deep research report on BCAT2 (falcon/Edison)
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      AI-generated deep-research synthesis (falcon/Edison). Used to corroborate the core BCAA
      catabolic pathway framing; primary catalytic/localization claims are independently grounded
      in UniProt O15382 and PMID:8702755/PMID:9165094.
- id: GO_REF:0000002
  title: Gene Ontology annotation through association of InterPro records with GO
    terms
  findings: []
- id: GO_REF:0000024
  title: Manual transfer of experimentally-verified manual GO annotation data to orthologs
    by curator judgment of sequence similarity
  findings: []
- id: GO_REF:0000033
  title: Annotation inferences using phylogenetic trees
  findings: []
- id: GO_REF:0000052
  title: Gene Ontology annotation based on curation of immunofluorescence data
  findings: []
- id: GO_REF:0000107
  title: Automatic transfer of experimentally verified manual GO annotation data to
    orthologs using Ensembl Compara
  findings: []
- id: GO_REF:0000116
  title: Automatic Gene Ontology annotation based on Rhea mapping
  findings: []
- id: GO_REF:0000117
  title: Electronic Gene Ontology annotations created by ARBA machine learning models
  findings: []
- id: GO_REF:0000120
  title: Combined Automated Annotation using Multiple IEA Methods
  findings: []
- id: PMID:28514442
  title: Architecture of the human interactome defines protein communities and disease
    networks.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      BioPlex 2.0 proteome-scale AP-MS; source of a bare "protein binding" IPI (interactors incl.
      HSPD1/P10809). PMC full text confirmed. Not informative about BCAT2's catalytic function.
- id: PMID:29568061
  title: An AP-MS- and BioID-compatible MAC-tag enables comprehensive mapping of protein
    interactions and subcellular localizations.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      MAC-tag AP-MS/BioID methods paper; source of a bare "protein binding" IPI. Uninformative about
      BCAT2 molecular function.
- id: PMID:33961781
  title: Dual proteome-scale networks reveal cell-specific remodeling of the human
    interactome.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      BioPlex 3.0 interactome; source of bare "protein binding" IPIs. Uninformative about catalytic
      function.
- id: PMID:34800366
  title: Quantitative high-confidence human mitochondrial proteome and its dynamics
    in cellular context.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      MitoCoP high-confidence mitochondrial proteome; supports mitochondrial localization (HTP).
      PMC full text confirmed.
- id: PMID:40205054
  title: Multimodal cell maps as a foundation for structural and functional genomics.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      Multimodal cell-map interactome; source of bare "protein binding" IPIs. Uninformative about
      catalytic function.
- id: PMID:8702755
  title: Two yeast homologs of ECA39, a target for c-Myc regulation, code for cytosolic
    and mitochondrial branched-chain amino acid aminotransferases.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Cached abstract-only (full_text_available: false); UniProt cites the full text (ECO:0000269)
      for the EC 2.6.1.42 catalytic activity and BCAA-catabolism FUNCTION. Directly establishes BCAT
      activity toward Leu/Ile/Val. Underlies the core MF and BP annotations.
- id: PMID:9165094
  title: Cloning of the rat and human mitochondrial branched chain aminotransferases
    (BCATm).
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Cached abstract-only; defining cloning paper that proposed BCAT1 (cytosolic)/BCAT2
      (mitochondrial) nomenclature, mapped BCAT2 to chromosome 19, and showed a 27-residue
      mitochondrial presequence and BCAT activity. Supports MF and mitochondrial localization.
- id: Reactome:R-HSA-508179
  title: "a-ketoisocaproate, a-keto-b-methylvalerate, or a-ketoisovalerate + glutamate"
  findings: []
- id: Reactome:R-HSA-70724
  title: "leu, ile, or val + alpha-ketoglutarate <=> a-ketoisocaproate, a-keto-b-methylvalerate,"
  findings: []
- id: UniProtKB:O35855
  title: Branched-chain-amino-acid aminotransferase, mitochondrial (Mus musculus)
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      Mouse ortholog UniProt entry; source of the By-similarity FUNCTION statement (BCAA-catabolism
      acetyl-CoA used by EP300 to acetylate/inhibit PRDM16, preventing adipose browning) underlying
      the ISS brown-fat annotations. Verbatim supporting text quoted from the human O15382 UniProt
      FUNCTION comment, which attributes the statement to O35855.