Component

The hydrophobic substrate channel of the cyclooxygenase active site

The hydrophobic substrate channel of the cyclooxygenase active site. Species, exposure and limitations are retained in each linked claim.

5 recorded relationships. Experimental role, claim status and evidence remain attached to each record.

Read recorded mechanisms Open recursive mind map

How nutrients influence it

Every nutrient with a recorded effect on this component, credited to the nutrient that acted rather than the chapter that recorded it. Open a nutrient to see the findings and the conditions they were measured under.

How nutrients reach it in more than one step

Chains of two or more recorded steps that end here, grouped by the nutrient they start from. Each step is a separate finding, so a chain is a route a mechanism could take, not proof that it does.

Tracing routes…

What it does

Every recorded relationship this component is part of, grouped by its role. Plain wording comes first; the technical statement follows.

Recorded relationships

What acts on it

  1. The crystal structures reveal that the acetylated Ser-530 completely blocks access to the hydrophobic groove, that the observed binding pose of salicylate is reflective of the enzyme-inhibitor complex prior to acetylation, and that the observed Thr-530 rotamer in the S530T mutant does not impede access to the groove; differential acetylation of COX-2 purified in various detergent systems and nanodiscs indicates that detergent and lipid binding within the membrane-binding domain alters the rate of the acetylation reaction in vitro.

    Aspirin-acetylated cyclooxygenase-2 → The hydrophobic substrate channel of the cyclooxygenase active site source_derived_draftungraded
    Experimental context and source evidence
    evidence_span
    {"source_cache": "artifacts/aspirin-research/26859324.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "2d5dab1d6b7576a909c9cef6b5c247e6a399946afbf7ef6d428d67475a363c34", "start_char": 0, "end_char": 1553, "text_sha256": "2d5dab1d6b7576a909c9cef6b5c247e6a399946afbf7ef6d428d67475a363c34"}
    experimental_model
    Crystal structures of an S530T murine COX-2 mutant, aspirin-acetylated human COX-2 and human COX-2 with salicylate, at 1.9 to 2.4 angstrom
    exposure
    Aspirin acetylation and salicylate binding, with an S530T/G533V double mutant and purification in several detergent systems
    limitations
    Much higher resolution than the 1995 structure and it captures salicylate separately. The authors note that detergent and lipid in the membrane-binding domain change the acetylation rate in vitro, which is a caution about all such measurements.
    nutrient_topic
    Aspirin research collection; topical membership is not evidence of a direct clinical effect, and aspirin is recorded separately from salicylate, the metabolite it becomes. · Aspirin / acetylsalicylic acid
    organism
    Mouse and human enzyme
    plain_language
    At high resolution the acetyl group seals the groove completely, and salicylate is caught sitting where aspirin sits before it reacts.
    primary_references
    [asa-p26859324] Crystal Structure of Aspirin-Acetylated Human Cyclooxygenase-2: Insight into the Formation of Products with Reversed Stereochemistry. (2016). https://pubmed.ncbi.nlm.nih.gov/26859324/ DOI: 10.1021/acs.biochem.5b01378
    tissue_or_cell_type
    Crystallised cyclooxygenase-2

    Aspirin: the serine it acetylates, the enzyme that acetylation creates, the dose that separates platelet from vessel wall, and the metabolite that is a different drug (2026-09-22) · lines 156–167

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Crystal structures of an S530T murine COX-2 mutant, aspirin-acetylated human COX-2 and human COX-2 with salicylate, at 1.9 to 2.4 angstrom · source_derived_draft · unverified_draft

    ### asa-acetyl-blocks-the-groove The crystal structures reveal that the acetylated Ser-530 completely blocks access to the hydrophobic groove, that the observed binding pose of salicylate is reflective of the enzyme-inhibitor complex prior to acetylation, and that the observed Thr-530 rotamer in the S530T mutant does not impede access to the groove; differential acetylation of COX-2 purified in various detergent systems and nanodiscs indicates that detergent and lipid binding within the membrane-binding domain alters the rate of the acetylation reaction in vitro. Condition category: normal nutrient_topic: Aspirin research collection; topical membership is not evidence of a direct clinical effect, and aspirin is recorded separately from salicylate, the metabolite it becomes. plain_language: At high resolution the acetyl group seals the groove completely, and salicylate is caught sitting where aspirin sits before it reacts. organism: Mouse and human enzyme tissue_or_cell_type: Crystallised cyclooxygenase-2 experimental_model: Crystal structures of an S530T murine COX-2 mutant, aspirin-acetylated human COX-2 and human COX-2 with salicylate, at 1.9 to 2.4 angstrom limitations: Much higher resolution than the 1995 structure and it captures salicylate separately. The authors note that detergent and lipid in the membrane-binding domain change the acetylation rate in vitro, which is a caution about all such measurements. exposure: Aspirin acetylation and salicylate binding, with an S530T/G533V double mutant and purification in several detergent systems evidence_span: {"source_cache": "artifacts/aspirin-research/26859324.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "2d5dab1d6b7576a909c9cef6b5c247e6a399946afbf7ef6d428d67475a363c34", "start_char": 0, "end_char": 1553, "text_sha256": "2d5dab1d6b7576a909c9cef6b5c247e6a399946afbf7ef6d428d67475a363c34"} [asa-p26859324] Crystal Structure of Aspirin-Acetylated Human Cyclooxygenase-2: Insight into the Formation of Products with Reversed Stereochemistry. (2016). https://pubmed.ncbi.nlm.nih.gov/26859324/ DOI: 10.1021/acs.biochem.5b01378
    Complete structured claim and evidence

  2. The 3.4 angstrom X-ray crystal structure of prostaglandin H2 synthase isoform-1 inactivated by the potent aspirin analogue 2-bromoacetoxy-benzoic acid shows that acetylation abolishes cyclooxygenase activity by steric blockage of the active-site channel and not through a large conformational change, with two rotameric states of the acetyl-serine side chain blocking the channel to different extents, a result which may explain the dissimilar effects of aspirin on the two isoforms.

    Aspirin-acetylated cyclooxygenase-1 → The hydrophobic substrate channel of the cyclooxygenase active site source_derived_draftungraded
    Experimental context and source evidence
    evidence_span
    {"source_cache": "artifacts/aspirin-research/7552725.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "dd61431f20eb312313942bc8a89f970d5d2e33600b32abe692f20d9d5c57d7b1", "start_char": 0, "end_char": 751, "text_sha256": "dd61431f20eb312313942bc8a89f970d5d2e33600b32abe692f20d9d5c57d7b1"}
    experimental_model
    X-ray crystal structure at 3.4 angstrom of prostaglandin H2 synthase-1 inactivated by a potent aspirin analogue
    exposure
    2-bromoacetoxy-benzoic acid acetylation, with salicylic acid soaked into the structure
    limitations
    Direct structural evidence rather than inference from mutants, though at modest resolution and using an analogue rather than aspirin itself.
    nutrient_topic
    Aspirin research collection; topical membership is not evidence of a direct clinical effect, and aspirin is recorded separately from salicylate, the metabolite it becomes. · Aspirin / acetylsalicylic acid
    organism
    Enzyme
    plain_language
    The picture confirms it: the acetyl group simply plugs the tunnel the fatty acid has to travel down.
    primary_references
    [asa-p7552725] The structural basis of aspirin activity inferred from the crystal structure of inactivated prostaglandin H2 synthase. (1995). https://pubmed.ncbi.nlm.nih.gov/7552725/ DOI: 10.1038/nsb0895-637
    tissue_or_cell_type
    Crystallised prostaglandin H2 synthase-1

    Aspirin: the serine it acetylates, the enzyme that acetylation creates, the dose that separates platelet from vessel wall, and the metabolite that is a different drug (2026-09-22) · lines 130–141

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · X-ray crystal structure at 3.4 angstrom of prostaglandin H2 synthase-1 inactivated by a potent aspirin analogue · source_derived_draft · unverified_draft

    ### asa-structure-shows-blockage The 3.4 angstrom X-ray crystal structure of prostaglandin H2 synthase isoform-1 inactivated by the potent aspirin analogue 2-bromoacetoxy-benzoic acid shows that acetylation abolishes cyclooxygenase activity by steric blockage of the active-site channel and not through a large conformational change, with two rotameric states of the acetyl-serine side chain blocking the channel to different extents, a result which may explain the dissimilar effects of aspirin on the two isoforms. Condition category: normal nutrient_topic: Aspirin research collection; topical membership is not evidence of a direct clinical effect, and aspirin is recorded separately from salicylate, the metabolite it becomes. plain_language: The picture confirms it: the acetyl group simply plugs the tunnel the fatty acid has to travel down. organism: Enzyme tissue_or_cell_type: Crystallised prostaglandin H2 synthase-1 experimental_model: X-ray crystal structure at 3.4 angstrom of prostaglandin H2 synthase-1 inactivated by a potent aspirin analogue limitations: Direct structural evidence rather than inference from mutants, though at modest resolution and using an analogue rather than aspirin itself. exposure: 2-bromoacetoxy-benzoic acid acetylation, with salicylic acid soaked into the structure evidence_span: {"source_cache": "artifacts/aspirin-research/7552725.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "dd61431f20eb312313942bc8a89f970d5d2e33600b32abe692f20d9d5c57d7b1", "start_char": 0, "end_char": 751, "text_sha256": "dd61431f20eb312313942bc8a89f970d5d2e33600b32abe692f20d9d5c57d7b1"} [asa-p7552725] The structural basis of aspirin activity inferred from the crystal structure of inactivated prostaglandin H2 synthase. (1995). https://pubmed.ncbi.nlm.nih.gov/7552725/ DOI: 10.1038/nsb0895-637
    Complete structured claim and evidence

Where it participates (unsigned role)

  1. In the crystal structure of the inactivated enzyme the product salicylic acid was observed binding at a site consistent with its antagonistic effect on aspirin activity.

    Salicylate / salicylic acid → Aspirin / acetylsalicylic acid source_derived_draftungraded
    Experimental context and source evidence
    evidence_span
    {"source_cache": "artifacts/aspirin-research/7552725.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "dd61431f20eb312313942bc8a89f970d5d2e33600b32abe692f20d9d5c57d7b1", "start_char": 0, "end_char": 751, "text_sha256": "dd61431f20eb312313942bc8a89f970d5d2e33600b32abe692f20d9d5c57d7b1"}
    experimental_model
    X-ray crystal structure at 3.4 angstrom of prostaglandin H2 synthase-1 inactivated by a potent aspirin analogue
    exposure
    2-bromoacetoxy-benzoic acid acetylation, with salicylic acid soaked into the structure
    limitations
    Direct structural evidence rather than inference from mutants, though at modest resolution and using an analogue rather than aspirin itself.
    nutrient_topic
    Aspirin research collection; topical membership is not evidence of a direct clinical effect, and aspirin is recorded separately from salicylate, the metabolite it becomes. · Aspirin / acetylsalicylic acid
    organism
    Enzyme
    plain_language
    The breakdown product sits in the same place the drug needs to reach, and gets in its way.
    primary_references
    [asa-p7552725] The structural basis of aspirin activity inferred from the crystal structure of inactivated prostaglandin H2 synthase. (1995). https://pubmed.ncbi.nlm.nih.gov/7552725/ DOI: 10.1038/nsb0895-637
    tissue_or_cell_type
    Crystallised prostaglandin H2 synthase-1

    Aspirin: the serine it acetylates, the enzyme that acetylation creates, the dose that separates platelet from vessel wall, and the metabolite that is a different drug (2026-09-22) · lines 143–154

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · X-ray crystal structure at 3.4 angstrom of prostaglandin H2 synthase-1 inactivated by a potent aspirin analogue · source_derived_draft · unverified_draft

    ### asa-salicylate-antagonises-at-the-site In the crystal structure of the inactivated enzyme the product salicylic acid was observed binding at a site consistent with its antagonistic effect on aspirin activity. Condition category: normal nutrient_topic: Aspirin research collection; topical membership is not evidence of a direct clinical effect, and aspirin is recorded separately from salicylate, the metabolite it becomes. plain_language: The breakdown product sits in the same place the drug needs to reach, and gets in its way. organism: Enzyme tissue_or_cell_type: Crystallised prostaglandin H2 synthase-1 experimental_model: X-ray crystal structure at 3.4 angstrom of prostaglandin H2 synthase-1 inactivated by a potent aspirin analogue limitations: Direct structural evidence rather than inference from mutants, though at modest resolution and using an analogue rather than aspirin itself. exposure: 2-bromoacetoxy-benzoic acid acetylation, with salicylic acid soaked into the structure evidence_span: {"source_cache": "artifacts/aspirin-research/7552725.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "dd61431f20eb312313942bc8a89f970d5d2e33600b32abe692f20d9d5c57d7b1", "start_char": 0, "end_char": 751, "text_sha256": "dd61431f20eb312313942bc8a89f970d5d2e33600b32abe692f20d9d5c57d7b1"} [asa-p7552725] The structural basis of aspirin activity inferred from the crystal structure of inactivated prostaglandin H2 synthase. (1995). https://pubmed.ncbi.nlm.nih.gov/7552725/ DOI: 10.1038/nsb0895-637
    Complete structured claim and evidence

  2. Diclofenac inhibition was unaffected by mutation of Arg-120 to alanine but was dramatically attenuated by the S530A mutation, and the crystal structure of diclofenac with murine COX-2 shows it bound in an inverted conformation with its carboxylate hydrogen-bonded to Tyr-385 and Ser-530, the first experimental demonstration that an acidic non-steroidal anti-inflammatory drug can bind in an orientation that precludes a salt bridge with Arg-120; Ser-530 is also important in time-dependent inhibition by nimesulide and piroxicam.

    Serine 530 of cyclooxygenase-1 → Diclofenac source_derived_draftungraded
    Experimental context and source evidence
    evidence_span
    {"source_cache": "artifacts/aspirin-research/12925531.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "732e941e7f912ae2495715634eabdef176dae39e32359609f15b05a230d5f6e0", "start_char": 0, "end_char": 1473, "text_sha256": "732e941e7f912ae2495715634eabdef176dae39e32359609f15b05a230d5f6e0"}
    experimental_model
    Site-directed mutants of COX-2 at Arg-120, Tyr-355, Tyr-348 and Ser-530 tested against a series of inhibitors, with a diclofenac co-crystal structure
    exposure
    Diclofenac, nimesulide and piroxicam against the mutant panel
    limitations
    Shows the acetylation serine is also a general binding determinant for other drugs. The structural work is on murine rather than human enzyme.
    nutrient_topic
    Aspirin research collection; topical membership is not evidence of a direct clinical effect, and aspirin is recorded separately from salicylate, the metabolite it becomes. · Aspirin / acetylsalicylic acid
    organism
    Mouse enzyme
    plain_language
    The same serine aspirin attacks is where several other anti-inflammatories anchor themselves.
    primary_references
    [asa-p12925531] A novel mechanism of cyclooxygenase-2 inhibition involving interactions with Ser-530 and Tyr-385. (2003). https://pubmed.ncbi.nlm.nih.gov/12925531/ DOI: 10.1074/jbc.m305481200
    tissue_or_cell_type
    Cyclooxygenase-2

    Aspirin: the serine it acetylates, the enzyme that acetylation creates, the dose that separates platelet from vessel wall, and the metabolite that is a different drug (2026-09-22) · lines 169–180

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Site-directed mutants of COX-2 at Arg-120, Tyr-355, Tyr-348 and Ser-530 tested against a series of inhibitors, with a diclofenac co-crystal structure · source_derived_draft · unverified_draft

    ### asa-ser530-binds-other-drugs Diclofenac inhibition was unaffected by mutation of Arg-120 to alanine but was dramatically attenuated by the S530A mutation, and the crystal structure of diclofenac with murine COX-2 shows it bound in an inverted conformation with its carboxylate hydrogen-bonded to Tyr-385 and Ser-530, the first experimental demonstration that an acidic non-steroidal anti-inflammatory drug can bind in an orientation that precludes a salt bridge with Arg-120; Ser-530 is also important in time-dependent inhibition by nimesulide and piroxicam. Condition category: normal nutrient_topic: Aspirin research collection; topical membership is not evidence of a direct clinical effect, and aspirin is recorded separately from salicylate, the metabolite it becomes. plain_language: The same serine aspirin attacks is where several other anti-inflammatories anchor themselves. organism: Mouse enzyme tissue_or_cell_type: Cyclooxygenase-2 experimental_model: Site-directed mutants of COX-2 at Arg-120, Tyr-355, Tyr-348 and Ser-530 tested against a series of inhibitors, with a diclofenac co-crystal structure limitations: Shows the acetylation serine is also a general binding determinant for other drugs. The structural work is on murine rather than human enzyme. exposure: Diclofenac, nimesulide and piroxicam against the mutant panel evidence_span: {"source_cache": "artifacts/aspirin-research/12925531.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "732e941e7f912ae2495715634eabdef176dae39e32359609f15b05a230d5f6e0", "start_char": 0, "end_char": 1473, "text_sha256": "732e941e7f912ae2495715634eabdef176dae39e32359609f15b05a230d5f6e0"} [asa-p12925531] A novel mechanism of cyclooxygenase-2 inhibition involving interactions with Ser-530 and Tyr-385. (2003). https://pubmed.ncbi.nlm.nih.gov/12925531/ DOI: 10.1074/jbc.m305481200
    Complete structured claim and evidence

  3. Although ibuprofen, naproxen and celecoxib all had the potential to compete with aspirin for access to the substrate binding channel of cyclooxygenase-1 in vitro, measuring aspirin target engagement directly by mass spectrometry after a single therapeutic dose of each followed by 325 milligrams of aspirin revealed a potent drug-drug interaction between ibuprofen and aspirin and between naproxen and aspirin but not between celecoxib and aspirin.

    Naproxen → Aspirin / acetylsalicylic acid source_derived_draftungraded
    Experimental context and source evidence
    availability_state
    biomarker_context Imported condition classification; unverified.
    evidence_span
    {"source_cache": "artifacts/aspirin-research/25385584.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "b2de8f18887f336c8c735f7ffbd1b72b92e5da43aa6388c229590dea120439f2", "start_char": 0, "end_char": 1242, "text_sha256": "b2de8f18887f336c8c735f7ffbd1b72b92e5da43aa6388c229590dea120439f2"}
    experimental_model
    Mass-spectrometric assay of cyclooxygenase-1 acetylation in platelets from volunteers given an NSAID followed by aspirin
    exposure
    A single therapeutic dose of ibuprofen, naproxen or celecoxib followed by 325 milligrams of aspirin
    limitations
    Measures target engagement directly rather than inferring it from platelet function, and separates the drugs. A single dose of each, in volunteers rather than patients.
    nutrient_topic
    Aspirin research collection; topical membership is not evidence of a direct clinical effect, and aspirin is recorded separately from salicylate, the metabolite it becomes. · Aspirin / acetylsalicylic acid
    organism
    Human
    plain_language
    Ibuprofen and naproxen block aspirin in people; celecoxib does not.
    primary_references
    [asa-p25385584] Differential impairment of aspirin-dependent platelet cyclooxygenase acetylation by nonsteroidal antiinflammatory drugs. (2014). https://pubmed.ncbi.nlm.nih.gov/25385584/ DOI: 10.1073/pnas.1406997111
    tissue_or_cell_type
    Platelets
    trigger_kind
    biomarker_context Imported condition classification; unverified.

    Aspirin: the serine it acetylates, the enzyme that acetylation creates, the dose that separates platelet from vessel wall, and the metabolite that is a different drug (2026-09-22) · lines 455–466

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Mass-spectrometric assay of cyclooxygenase-1 acetylation in platelets from volunteers given an NSAID followed by aspirin · source_derived_draft · unverified_draft

    ### asa-which-nsaids-interact Although ibuprofen, naproxen and celecoxib all had the potential to compete with aspirin for access to the substrate binding channel of cyclooxygenase-1 in vitro, measuring aspirin target engagement directly by mass spectrometry after a single therapeutic dose of each followed by 325 milligrams of aspirin revealed a potent drug-drug interaction between ibuprofen and aspirin and between naproxen and aspirin but not between celecoxib and aspirin. Condition category: biomarker_context nutrient_topic: Aspirin research collection; topical membership is not evidence of a direct clinical effect, and aspirin is recorded separately from salicylate, the metabolite it becomes. plain_language: Ibuprofen and naproxen block aspirin in people; celecoxib does not. organism: Human tissue_or_cell_type: Platelets experimental_model: Mass-spectrometric assay of cyclooxygenase-1 acetylation in platelets from volunteers given an NSAID followed by aspirin limitations: Measures target engagement directly rather than inferring it from platelet function, and separates the drugs. A single dose of each, in volunteers rather than patients. exposure: A single therapeutic dose of ibuprofen, naproxen or celecoxib followed by 325 milligrams of aspirin evidence_span: {"source_cache": "artifacts/aspirin-research/25385584.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "b2de8f18887f336c8c735f7ffbd1b72b92e5da43aa6388c229590dea120439f2", "start_char": 0, "end_char": 1242, "text_sha256": "b2de8f18887f336c8c735f7ffbd1b72b92e5da43aa6388c229590dea120439f2"} [asa-p25385584] Differential impairment of aspirin-dependent platelet cyclooxygenase acetylation by nonsteroidal antiinflammatory drugs. (2014). https://pubmed.ncbi.nlm.nih.gov/25385584/ DOI: 10.1073/pnas.1406997111
    Complete structured claim and evidence

In the sources

Preserved passages that mention this component, quoted exactly. Open one to read it in context.

    This is a research prototype built from draft material. It is not medical advice, and its statements still await verification against the original studies.

    Evidence, AI assistance and curation standards