id: O15067
gene_symbol: PFAS
product_type: PROTEIN
status: INITIALIZED
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: >-
  PFAS encodes phosphoribosylformylglycinamidine synthase (FGAM synthase; also called
  FGAR amidotransferase, FGARAT; EC 6.3.5.3), the enzyme that carries out the fourth step
  of de novo purine synthesis. It catalyses the ATP-dependent, glutamine-dependent
  amidotransfer that converts formylglycinamide ribonucleotide (FGAR) to formylglycinamidine
  ribonucleotide (FGAM), releasing L-glutamate, ADP and phosphate (FGAR + L-glutamine + ATP
  + H2O -> FGAM + L-glutamate + ADP + Pi). The multidomain protein combines an N-terminal
  ATP-/Mg2+-dependent synthetase (PurL) region with a C-terminal class-I glutamine
  amidotransferase (GATase-1) domain that hydrolyses glutamine to supply the transferred
  amide nitrogen. The enzyme is cytosolic and can associate with the purinosome, the
  reversible multi-enzyme assembly of de novo purine synthesis. As one of the six enzymes of
  this housekeeping pathway it supplies the inosine monophosphate (IMP) precursor from which
  AMP and GMP are subsequently made, and its activity is of interest in the elevated
  nucleotide demand of proliferating and cancer cells.
existing_annotations:
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: is_active_in
  review:
    summary: >-
      Phylogenetically inferred cytoplasmic localization for this cytosolic de novo purine
      synthesis enzyme. Consistent with the UniProt subcellular location and with Reactome's
      cytosol assignment.
    action: ACCEPT
    reason: >-
      PFAS is a soluble cytosolic enzyme with no membrane-spanning or targeting features; the
      IBA cytoplasm annotation is correct, though the more specific cytosol term (GO:0005829)
      is preferable as the primary localization.
    supported_by:
    - reference_id: file:human/PFAS/PFAS-uniprot.txt
      supporting_text: "SUBCELLULAR LOCATION: Cytoplasm"
    - reference_id: Reactome:R-HSA-73812
      supporting_text: >-
        Fluoresence microscopy studies of cultured human cells have shown that the enzyme is
        cytosolic
- term:
    id: GO:0004642
    label: phosphoribosylformylglycinamidine synthase activity
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: enables
  review:
    summary: >-
      Phylogenetically inferred phosphoribosylformylglycinamidine synthase (FGAM synthase)
      activity, the defining molecular function of PFAS and its orthologs across the FGAMS
      family.
    action: ACCEPT
    reason: >-
      This is the core molecular function of PFAS, EC 6.3.5.3 (RHEA:17129), independently
      supported by direct biochemical evidence (IDA) and by the conserved N-terminal PurL
      synthetase plus C-terminal GATase-1 domain architecture in UniProt.
    supported_by:
    - reference_id: file:human/PFAS/PFAS-uniprot.txt
      supporting_text: "RecName: Full=Phosphoribosylformylglycinamidine synthase;"
    - reference_id: file:human/PFAS/PFAS-uniprot.txt
      supporting_text: purines biosynthetic pathway. Catalyzes the ATP-dependent conversion of
- term:
    id: GO:0006164
    label: purine nucleotide biosynthetic process
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: >-
      Phylogenetically inferred involvement in purine nucleotide biosynthesis, the pathway
      to which the FGAM synthase reaction belongs.
    action: ACCEPT
    reason: >-
      Correct parent biological process. PFAS performs step four of de novo purine synthesis,
      producing the IMP precursor from which purine nucleotides are made. This broad term is
      accurate; the more specific 'de novo IMP biosynthetic process' (GO:0006189) is also
      annotated and captured as core.
    supported_by:
    - reference_id: PMID:10548741
      supporting_text: >-
        phosphoribosylformylglycineamide amidotransferase (FGARAT) gene, which
        encodes the fourth step of this pathway
- term:
    id: GO:0004642
    label: phosphoribosylformylglycinamidine synthase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: enables
  review:
    summary: >-
      Electronic assignment of FGAM synthase activity from InterPro/EC/RHEA mappings
      (IPR010073, EC 6.3.5.3, RHEA:17129).
    action: ACCEPT
    reason: >-
      Correct and specific. The InterPro-to-GO and EC mappings identify the exact catalytic
      function, in agreement with the IBA, TAS and IDA annotations of the same term.
    supported_by:
    - reference_id: file:human/PFAS/PFAS-uniprot.txt
      supporting_text: "RecName: Full=Phosphoribosylformylglycinamidine synthase;"
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  qualifier: located_in
  review:
    summary: >-
      Electronic cytoplasm localization from the UniProt subcellular-location keyword mapping
      (SL-0086).
    action: ACCEPT
    reason: >-
      Consistent with the manually asserted cytoplasmic/cytosolic localization; correct
      though less specific than cytosol.
    supported_by:
    - reference_id: file:human/PFAS/PFAS-uniprot.txt
      supporting_text: "SUBCELLULAR LOCATION: Cytoplasm"
- term:
    id: GO:0006189
    label: "'de novo' IMP biosynthetic process"
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: involved_in
  review:
    summary: >-
      Electronic assignment (InterPro IPR010073, UniPathway UPA00074) placing PFAS in the de
      novo IMP biosynthetic pathway.
    action: ACCEPT
    reason: >-
      This is the specific and correct biological process for PFAS: the FGAR->FGAM step is
      part of the de novo pathway that builds IMP. Concordant with the IDA and NAS annotations
      of the same term.
    supported_by:
    - reference_id: file:human/PFAS/PFAS-uniprot.txt
      supporting_text: "IMP biosynthesis via de novo pathway"
    - reference_id: PMID:10548741
      supporting_text: >-
        The de-novo
        synthesis of purines requires 10 enzymatic steps for the production of inosine
        monophosphate (IMP)
- term:
    id: GO:0006541
    label: L-glutamine metabolic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Electronic annotation transferred from a rat ortholog (UniProtKB:D4AB17) capturing that
      PFAS consumes L-glutamine as the amide-nitrogen donor for the amidotransfer reaction.
    action: KEEP_AS_NON_CORE
    reason: >-
      Biologically reasonable - the C-terminal glutamine amidotransferase (GATase-1) domain
      hydrolyses glutamine to supply the transferred nitrogen, so PFAS participates in
      glutamine catabolism as a side/co-substrate process. However this is a consequence of
      the catalytic mechanism rather than the enzyme's core role, which is purine
      (IMP-precursor) biosynthesis; retain as non-core.
    supported_by:
    - reference_id: file:human/PFAS/PFAS-uniprot.txt
      supporting_text: "ATP-binding; Cytoplasm; Glutamine amidotransferase; Ligase; Magnesium;"
- term:
    id: GO:0009410
    label: response to xenobiotic stimulus
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Electronic annotation transferred from a rat ortholog (UniProtKB:D4AB17,
      ENSRNOP00000007087) via Ensembl Compara.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      This term reflects a downstream expression/response phenotype observed for the rodent
      ortholog and does not describe the molecular or biosynthetic role of PFAS. For a
      housekeeping de novo purine synthesis enzyme this is an over-annotation transferred
      electronically from an ortholog; it is not a core function of human PFAS and there is no
      direct evidence for it in this gene.
- term:
    id: GO:0009168
    label: purine ribonucleoside monophosphate biosynthetic process
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-73817
  qualifier: involved_in
  review:
    summary: >-
      Reactome pathway-level assertion that PFAS participates in purine ribonucleoside
      monophosphate (IMP) biosynthesis.
    action: ACCEPT
    reason: >-
      Correct pathway-level process. Reactome places the FGAR->FGAM reaction within the
      pathway that assembles IMP on PRPP; equivalent in scope to the de novo IMP biosynthetic
      process term.
    supported_by:
    - reference_id: Reactome:R-HSA-73817
      supporting_text: >-
        The purine ribonucleotide inosine 5'-monophosphate (IMP) is assembled on
        5-phospho-alpha-D-ribose 1-diphosphate (PRPP)
- term:
    id: GO:0004642
    label: phosphoribosylformylglycinamidine synthase activity
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-73812
  qualifier: enables
  review:
    summary: >-
      Reactome traceable assertion of FGAM synthase activity, citing the biochemically
      characterized human enzyme reaction FGAR + L-glutamine + ATP + H2O -> FGAM + L-glutamate
      + ADP + Pi.
    action: ACCEPT
    reason: >-
      Core molecular function, supported by the purified/characterized human enzyme and
      concordant with the IDA, IBA and IEA annotations of the same term.
    supported_by:
    - reference_id: Reactome:R-HSA-73812
      supporting_text: >-
        is catalyzed by phosphoribosylformylglycinamidine
        synthetase.  The human enzyme has been purified and characterized biochemically
- term:
    id: GO:0004642
    label: phosphoribosylformylglycinamidine synthase activity
  evidence_type: IMP
  original_reference_id: PMID:27590927
  qualifier: enables
  review:
    summary: >-
      FGAM synthase activity inferred from a CRISPR-Cas9 PFAS knockout in HeLa cells, in which
      loss of the enzyme causes accumulation of its substrate.
    action: ACCEPT
    reason: >-
      MGI experimental (IMP) annotation. The knockout phenotype - accumulation of the enzyme's
      substrate - directly implicates PFAS in the FGAR->FGAM step, supporting the core
      molecular function. The cached record is abstract-only; the full text (which the curator
      read) assays this DNPS step. Concordant with the independent IDA annotation.
    supported_by:
    - reference_id: PMID:27590927
      supporting_text: >-
        In all model cell lines with the exception
        of one, an accumulation of the substrate(s) for the knocked out enzyme was
        identified
- term:
    id: GO:0006177
    label: GMP biosynthetic process
  evidence_type: IMP
  original_reference_id: PMID:27590927
  qualifier: acts_upstream_of_or_within
  review:
    summary: >-
      From the CRISPR knockout study; loss of PFAS depletes de novo purine synthesis and
      thereby the downstream GMP branch.
    action: KEEP_AS_NON_CORE
    reason: >-
      PFAS acts upstream of GMP synthesis - it makes the IMP precursor, from which GMP is
      subsequently derived - so the acts_upstream_of_or_within qualifier is appropriate. It is
      not itself a GMP-biosynthesis enzyme, so this is a valid but non-core downstream-branch
      annotation.
    supported_by:
    - reference_id: PMID:27590927
      supporting_text: >-
        CRISPR-Cas9 genome-edited HeLa
        cells deficient for the individual steps
        of DNPS
- term:
    id: GO:0006189
    label: "'de novo' IMP biosynthetic process"
  evidence_type: IMP
  original_reference_id: PMID:27590927
  qualifier: acts_upstream_of_or_within
  review:
    summary: >-
      CRISPR knockout evidence that PFAS is required for de novo IMP biosynthesis, the pathway
      it directly participates in.
    action: ACCEPT
    reason: >-
      Core biological process, experimentally supported. Loss of PFAS blocks flux through de
      novo purine synthesis toward IMP; concordant with the involved_in IDA/NAS annotations of
      the same term.
    supported_by:
    - reference_id: PMID:27590927
      supporting_text: >-
        DNPS includes ten reactions catalysed by six enzymes.
- term:
    id: GO:0044208
    label: "'de novo' AMP biosynthetic process"
  evidence_type: IMP
  original_reference_id: PMID:27590927
  qualifier: acts_upstream_of_or_within
  review:
    summary: >-
      From the CRISPR knockout study; loss of PFAS depletes de novo purine synthesis and
      thereby the downstream AMP branch.
    action: KEEP_AS_NON_CORE
    reason: >-
      PFAS acts upstream of AMP synthesis by supplying the shared IMP precursor; the
      acts_upstream_of_or_within qualifier is correct. It is not itself an AMP-biosynthesis
      enzyme, so this is a valid but non-core downstream-branch annotation.
    supported_by:
    - reference_id: PMID:27590927
      supporting_text: >-
        CRISPR-Cas9 genome-edited HeLa
        cells deficient for the individual steps
        of DNPS
- term:
    id: GO:0097294
    label: "'de novo' XMP biosynthetic process"
  evidence_type: IMP
  original_reference_id: PMID:27590927
  qualifier: acts_upstream_of_or_within
  review:
    summary: >-
      From the CRISPR knockout study; loss of PFAS depletes de novo purine synthesis and
      thereby the downstream XMP branch.
    action: KEEP_AS_NON_CORE
    reason: >-
      PFAS acts upstream of XMP synthesis by supplying the shared IMP precursor; the
      acts_upstream_of_or_within qualifier is correct. It is not itself an XMP-biosynthesis
      enzyme, so this is a valid but non-core downstream-branch annotation.
    supported_by:
    - reference_id: PMID:27590927
      supporting_text: >-
        CRISPR-Cas9 genome-edited HeLa
        cells deficient for the individual steps
        of DNPS
- term:
    id: GO:0097294
    label: "'de novo' XMP biosynthetic process"
  evidence_type: IDA
  original_reference_id: PMID:27590927
  qualifier: involved_in
  review:
    summary: >-
      Direct-assay (IDA) annotation to the downstream de novo XMP branch, from the DNPS
      substrate-accumulation study.
    action: KEEP_AS_NON_CORE
    reason: >-
      With the involved_in qualifier this term is arguably too downstream for PFAS, whose
      direct reaction produces the IMP precursor rather than XMP. The corresponding
      acts_upstream_of_or_within annotation captures the relationship more accurately. Retained
      as non-core; deferring to the MGI curator's full-text reading rather than removing an
      experimental annotation.
    supported_by:
    - reference_id: PMID:27590927
      supporting_text: >-
        an accumulation of the substrate(s) for the knocked out enzyme was
        identified
- term:
    id: GO:0004642
    label: phosphoribosylformylglycinamidine synthase activity
  evidence_type: IDA
  original_reference_id: PMID:27590927
  qualifier: enables
  review:
    summary: >-
      Direct experimental evidence for FGAM synthase activity from the CRISPR/substrate-
      accumulation study.
    action: ACCEPT
    reason: >-
      Core molecular function with direct experimental support; concordant with the IMP, IBA,
      IEA and Reactome-TAS annotations of the same term.
    supported_by:
    - reference_id: PMID:27590927
      supporting_text: >-
        an accumulation of the substrate(s) for the knocked out enzyme was
        identified
- term:
    id: GO:0006177
    label: GMP biosynthetic process
  evidence_type: IDA
  original_reference_id: PMID:27590927
  qualifier: involved_in
  review:
    summary: >-
      Direct-assay (IDA) involved_in annotation to the downstream GMP branch.
    action: KEEP_AS_NON_CORE
    reason: >-
      As with the AMP/XMP branch terms, PFAS supplies the upstream IMP precursor rather than
      catalysing GMP synthesis; the acts_upstream_of_or_within relationship is more accurate
      than involved_in. Retained as non-core; not removed, as this is an experimental
      annotation whose full text the curator read.
    supported_by:
    - reference_id: PMID:27590927
      supporting_text: >-
        an accumulation of the substrate(s) for the knocked out enzyme was
        identified
- term:
    id: GO:0006189
    label: "'de novo' IMP biosynthetic process"
  evidence_type: IDA
  original_reference_id: PMID:27590927
  qualifier: involved_in
  review:
    summary: >-
      Direct-assay evidence that PFAS is involved in de novo IMP biosynthesis.
    action: ACCEPT
    reason: >-
      Core biological process. This is the pathway PFAS directly participates in (step four),
      and involved_in is the correct qualifier. Concordant with the IEA, NAS and Reactome
      annotations.
    supported_by:
    - reference_id: PMID:27590927
      supporting_text: >-
        DNPS includes ten reactions catalysed by six enzymes.
- term:
    id: GO:0044208
    label: "'de novo' AMP biosynthetic process"
  evidence_type: IDA
  original_reference_id: PMID:27590927
  qualifier: involved_in
  review:
    summary: >-
      Direct-assay (IDA) involved_in annotation to the downstream de novo AMP branch.
    action: KEEP_AS_NON_CORE
    reason: >-
      PFAS makes the shared IMP precursor upstream of AMP synthesis; involved_in is arguably
      too downstream, and the acts_upstream_of_or_within annotation captures the relationship
      better. Retained as valid but non-core; not removed given experimental support.
    supported_by:
    - reference_id: PMID:27590927
      supporting_text: >-
        an accumulation of the substrate(s) for the knocked out enzyme was
        identified
- term:
    id: GO:0070062
    label: extracellular exosome
  evidence_type: HDA
  original_reference_id: PMID:20458337
  qualifier: located_in
  review:
    summary: >-
      High-throughput MS detection of PFAS among 539 proteins in the total proteome of
      purified B-cell-derived exosomes.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      This is a bulk mass-spectrometry catalog of an exosome preparation, not a targeted or
      functionally meaningful localization for a cytosolic de novo purine synthesis enzyme.
      Abundant cytosolic proteins are routinely detected in such exosome proteomes; there is
      no evidence of a functional role for PFAS in exosomes. Over-annotation - the enzyme acts
      in the cytosol.
    supported_by:
    - reference_id: PMID:20458337
      supporting_text: >-
        we first analyzed the total
        proteome of highly purified B cell-derived exosomes using sensitive and accurate
        mass spectrometry (MS), and identified 539 proteins
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-73812
  qualifier: located_in
  review:
    summary: >-
      Reactome traceable assertion that the enzyme is cytosolic, from fluorescence microscopy
      of cultured human cells.
    action: ACCEPT
    reason: >-
      Most specific and accurate cellular-component annotation for PFAS. Cytosolic
      localization is consistent with the enzyme's role in de novo purine synthesis and with
      its reversible association with the cytosolic purinosome.
    supported_by:
    - reference_id: Reactome:R-HSA-73812
      supporting_text: >-
        Fluoresence microscopy studies of cultured human cells have
        shown that the enzyme is cytosolic
- term:
    id: GO:0004642
    label: phosphoribosylformylglycinamidine synthase activity
  evidence_type: IDA
  original_reference_id: PMID:10548741
  qualifier: enables
  review:
    summary: >-
      Direct experimental evidence for FGAM synthase (FGARAT) activity: the human genomic
      clone corrects the purine auxotrophy and enzyme/protein deficiency of AdeB CHO mutants
      that lack FGARAT.
    action: ACCEPT
    reason: >-
      Core molecular function established by functional complementation. Restoring FGARAT
      activity in an enzyme-deficient mammalian cell line directly demonstrates the catalytic
      function of the encoded protein.
    supported_by:
    - reference_id: PMID:10548741
      supporting_text: >-
        The P1 clone corrects the purine auxotrophy and protein deficiency of Chinese
        hamster ovary (CHO) cell mutants (AdeB) deficient in both the activity and the
        protein for FGARAT.
- term:
    id: GO:0006189
    label: "'de novo' IMP biosynthetic process"
  evidence_type: NAS
  original_reference_id: PMID:10548741
  qualifier: involved_in
  review:
    summary: >-
      Non-traceable author statement placing FGARAT/PFAS as the fourth of the ten enzymatic
      steps producing IMP by de novo purine synthesis.
    action: ACCEPT
    reason: >-
      Core biological process, consistent with the specific and correct pathway role of PFAS
      and concordant with the IEA/IDA annotations of the same term.
    supported_by:
    - reference_id: PMID:10548741
      supporting_text: >-
        phosphoribosylformylglycineamide amidotransferase (FGARAT) gene, which
        encodes the fourth step of this pathway
core_functions:
- description: >-
    Phosphoribosylformylglycinamidine synthase (FGAM synthase, FGARAT; EC 6.3.5.3): the
    ATP- and glutamine-dependent amidotransferase catalysing step four of de novo purine
    synthesis, converting FGAR to FGAM.
  molecular_function:
    id: GO:0004642
    label: phosphoribosylformylglycinamidine synthase activity
  directly_involved_in:
  - id: GO:0006189
    label: "'de novo' IMP biosynthetic process"
  locations:
  - id: GO:0005829
    label: cytosol
  supported_by:
  - reference_id: file:human/PFAS/PFAS-uniprot.txt
    supporting_text: "RecName: Full=Phosphoribosylformylglycinamidine synthase;"
  - reference_id: PMID:10548741
    supporting_text: >-
      phosphoribosylformylglycineamide amidotransferase (FGARAT) gene, which
      encodes the fourth step of this pathway
- description: >-
    Participation in purine nucleotide biosynthesis: by producing the FGAM intermediate en
    route to IMP, PFAS provides the precursor for downstream AMP and GMP synthesis.
  molecular_function:
    id: GO:0004642
    label: phosphoribosylformylglycinamidine synthase activity
  directly_involved_in:
  - id: GO:0006164
    label: purine nucleotide biosynthetic process
  locations:
  - id: GO:0005829
    label: cytosol
  supported_by:
  - reference_id: Reactome:R-HSA-73812
    supporting_text: >-
      is catalyzed by phosphoribosylformylglycinamidine
      synthetase.  The human enzyme has been purified and characterized biochemically
references:
- id: GO_REF:0000033
  title: Annotation inferences using phylogenetic trees
  findings: []
- id: GO_REF:0000044
  title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location
    vocabulary mapping, accompanied by conservative changes to GO terms applied by
    UniProt
  findings: []
- id: GO_REF:0000107
  title: Automatic transfer of experimentally verified manual GO annotation data to
    orthologs using Ensembl Compara
  findings: []
- id: GO_REF:0000120
  title: Combined Automated Annotation using Multiple IEA Methods
  findings: []
- id: PMID:10548741
  title: 'Human phosphoribosylformylglycineamide amidotransferase (FGARAT): regional
    mapping, complete coding sequence, isolation of a functional genomic clone, and
    DNA sequence analysis.'
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Cloning/complementation paper for human FGARAT/PFAS; establishes the enzyme as step
      four of de novo purine synthesis and demonstrates catalytic function by AdeB CHO
      complementation. Source of the IDA MF and NAS BP annotations. Abstract-only in cache.
- id: PMID:20458337
  title: MHC class II-associated proteins in B-cell exosomes and potential functional
    implications for exosome biogenesis.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      B-cell exosome proteomics (539 proteins). PFAS is a bulk-catalog hit; supports only the
      over-annotated extracellular-exosome CC, not a functional role.
- id: PMID:27590927
  title: CRISPR-Cas9 induced mutations along de novo purine synthesis in HeLa cells
    result in accumulation of individual enzyme substrates and affect purinosome formation.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      CRISPR knockouts of individual DNPS enzymes in HeLa; substrate accumulation and impaired
      purinosome assembly. Source of the MGI IMP/IDA annotations. Abstract frames DNPS at the
      pathway level without naming PFAS; full text (uncached) assays the FGAR-AT step, so
      deferring to the MGI curator.
- id: Reactome:R-HSA-73812
  title: FGAR + L-Glutamine + ATP + H2O => FGAM + L-Glutamate + ADP + Pi
  findings: []
- id: Reactome:R-HSA-73817
  title: Purine ribonucleoside monophosphate biosynthesis
  findings: []
- id: file:human/PFAS/PFAS-uniprot.txt
  title: UniProtKB entry O15067 (PUR4_HUMAN), phosphoribosylformylglycinamidine synthase
  findings: []
suggested_questions:
- question: >-
    Does PFAS have any moonlighting or regulatory function beyond de novo purine synthesis
    (e.g. in stress-granule/CD-CODE contexts or via its multiple phosphosites)?
- question: >-
    How does purinosome association modulate PFAS flux, and is the enzyme rate-limiting under
    conditions of high purine demand such as tumor proliferation?
suggested_experiments:
- description: >-
    Quantitative metabolic-flux analysis (LC-MS/MS of FGAR vs FGAM) in PFAS-null versus
    rescued cells to confirm the in vivo FGAR->FGAM step and measure control strength.
- description: >-
    Phospho-site mutagenesis (Ser215/Ser569/Thr619/Thr623) to test whether phosphorylation
    regulates PFAS activity or purinosome recruitment.