Component

Serine 530 of cyclooxygenase-1

Serine 530 of cyclooxygenase-1. Species, exposure and limitations are retained in each linked claim.

8 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 it acts on

  1. Using site-directed mutagenesis to prepare five further substitutions of Ser-530, the presence of amino acids with bulky side chains at position 530 inhibited cyclooxygenase activity and decreased the apparent affinity of the enzyme for arachidonate, consistent with the proposal that aspirin inhibits by placing a larger than normal side chain at position 530; residues 529 to 533 all proved important for the peroxidase as well as the cyclooxygenase activity, and Phe-529 in particular was critical for structure and catalysis.

    Serine 530 of cyclooxygenase-1 → Binding of arachidonate in the cyclooxygenase active site source_derived_draftungraded
    Experimental context and source evidence
    evidence_span
    {"source_cache": "artifacts/aspirin-research/1601897.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "616cbc367eb38194b858872cbf91108baa3b1dec7aa039a40f69a29fa7157c2d", "start_char": 0, "end_char": 1744, "text_sha256": "616cbc367eb38194b858872cbf91108baa3b1dec7aa039a40f69a29fa7157c2d"}
    experimental_model
    Five further substitutions at Ser-530 and substitutions at adjoining residues, expressed transiently in cos-1 cells
    exposure
    A graded series of side chains at position 530, plus substitutions at Phe-529, Leu-531, Lys-532 and Gly-533
    limitations
    Tests the steric hypothesis by varying the bulk systematically rather than with one mutant. Transient expression in a heterologous cell line.
    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 bigger the group put at that position, the worse the enzyme binds its substrate.
    primary_references
    [asa-p1601897] Prostaglandin endoperoxide synthase. The aspirin acetylation region. (1992). https://pubmed.ncbi.nlm.nih.gov/1601897/ DOI: 10.1016/s0021-9258(19)49852-9
    tissue_or_cell_type
    Recombinant prostaglandin endoperoxide H 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 117–128

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Five further substitutions at Ser-530 and substitutions at adjoining residues, expressed transiently in cos-1 cells · source_derived_draft · unverified_draft

    ### asa-graded-bulk-series Using site-directed mutagenesis to prepare five further substitutions of Ser-530, the presence of amino acids with bulky side chains at position 530 inhibited cyclooxygenase activity and decreased the apparent affinity of the enzyme for arachidonate, consistent with the proposal that aspirin inhibits by placing a larger than normal side chain at position 530; residues 529 to 533 all proved important for the peroxidase as well as the cyclooxygenase activity, and Phe-529 in particular was critical for structure and catalysis. 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 bigger the group put at that position, the worse the enzyme binds its substrate. organism: Enzyme tissue_or_cell_type: Recombinant prostaglandin endoperoxide H synthase-1 experimental_model: Five further substitutions at Ser-530 and substitutions at adjoining residues, expressed transiently in cos-1 cells limitations: Tests the steric hypothesis by varying the bulk systematically rather than with one mutant. Transient expression in a heterologous cell line. exposure: A graded series of side chains at position 530, plus substitutions at Phe-529, Leu-531, Lys-532 and Gly-533 evidence_span: {"source_cache": "artifacts/aspirin-research/1601897.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "616cbc367eb38194b858872cbf91108baa3b1dec7aa039a40f69a29fa7157c2d", "start_char": 0, "end_char": 1744, "text_sha256": "616cbc367eb38194b858872cbf91108baa3b1dec7aa039a40f69a29fa7157c2d"} [asa-p1601897] Prostaglandin endoperoxide synthase. The aspirin acetylation region. (1992). https://pubmed.ncbi.nlm.nih.gov/1601897/ DOI: 10.1016/s0021-9258(19)49852-9
    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

What acts on it

  1. Acetylation of Ser-530 of sheep prostaglandin endoperoxide synthase by aspirin causes irreversible inactivation of the cyclooxygenase activity of the enzyme, and since the serine hydroxyl is not required for catalysis the acetylation apparently introduces a bulky side chain at position 530 which interferes with arachidonate binding; a sequence of 35 residues with Ser-530 at the midpoint was identical in the sheep and mouse enzymes.

    Aspirin / acetylsalicylic acid → Serine 530 of cyclooxygenase-1 source_derived_draftungraded
    Experimental context and source evidence
    evidence_span
    {"source_cache": "artifacts/aspirin-research/2108169.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "c7b11508521a3854b432f3836de6e92ba9863c8edb244d747bb1c37634c0bb50", "start_char": 0, "end_char": 2076, "text_sha256": "c7b11508521a3854b432f3836de6e92ba9863c8edb244d747bb1c37634c0bb50"}
    experimental_model
    Site-directed mutagenesis of sheep prostaglandin endoperoxide synthase expressed in Cos-1 cells
    exposure
    Serine 530 replaced with alanine, compared with the native enzyme against aspirin and reversible inhibitors
    limitations
    The decisive experiment for the mechanism: it separates what the serine does for catalysis from what acetylating it does. Recombinant sheep enzyme, not human enzyme in a tissue.
    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
    Sheep and mouse enzyme
    plain_language
    The acetyl group works by being in the way, not by removing something the enzyme needed.
    primary_references
    [asa-p2108169] The aspirin and heme-binding sites of ovine and murine prostaglandin endoperoxide synthases. (1990). https://pubmed.ncbi.nlm.nih.gov/2108169/ DOI: 10.1016/s0021-9258(19)34105-5
    tissue_or_cell_type
    Recombinant enzyme in Cos-1 cells

    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 91–102

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Site-directed mutagenesis of sheep prostaglandin endoperoxide synthase expressed in Cos-1 cells · source_derived_draft · unverified_draft

    ### asa-acetylation-is-steric Acetylation of Ser-530 of sheep prostaglandin endoperoxide synthase by aspirin causes irreversible inactivation of the cyclooxygenase activity of the enzyme, and since the serine hydroxyl is not required for catalysis the acetylation apparently introduces a bulky side chain at position 530 which interferes with arachidonate binding; a sequence of 35 residues with Ser-530 at the midpoint was identical in the sheep and mouse enzymes. 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 acetyl group works by being in the way, not by removing something the enzyme needed. organism: Sheep and mouse enzyme tissue_or_cell_type: Recombinant enzyme in Cos-1 cells experimental_model: Site-directed mutagenesis of sheep prostaglandin endoperoxide synthase expressed in Cos-1 cells limitations: The decisive experiment for the mechanism: it separates what the serine does for catalysis from what acetylating it does. Recombinant sheep enzyme, not human enzyme in a tissue. exposure: Serine 530 replaced with alanine, compared with the native enzyme against aspirin and reversible inhibitors evidence_span: {"source_cache": "artifacts/aspirin-research/2108169.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "c7b11508521a3854b432f3836de6e92ba9863c8edb244d747bb1c37634c0bb50", "start_char": 0, "end_char": 2076, "text_sha256": "c7b11508521a3854b432f3836de6e92ba9863c8edb244d747bb1c37634c0bb50"} [asa-p2108169] The aspirin and heme-binding sites of ovine and murine prostaglandin endoperoxide synthases. (1990). https://pubmed.ncbi.nlm.nih.gov/2108169/ DOI: 10.1016/s0021-9258(19)34105-5
    Complete structured claim and evidence

Where it participates (unsigned role)

  1. Valeryl (pentanoyl) salicylate was the only compound of eight acyl salicylates to show isozyme selectivity and inhibited human cyclooxygenase-1 much more effectively than cyclooxygenase-2 in a time-dependent manner, inhibited ovine cyclooxygenase-1 but did not inhibit the S530A mutant of ovine cyclooxygenase-1 which is also refractory to acetylsalicylate, so valeryl salicylate acylates the active site serine.

    Valeryl (pentanoyl) salicylate → Cyclooxygenase-1 (PTGS1) source_derived_draftungraded
    Experimental context and source evidence
    evidence_span
    {"source_cache": "artifacts/aspirin-research/7872783.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "f7e8a07a2704cb600938505ec51355671355769c01868ed0966731382901425b", "start_char": 0, "end_char": 1756, "text_sha256": "f7e8a07a2704cb600938505ec51355671355769c01868ed0966731382901425b"}
    experimental_model
    Eight acyl salicylates tested against human cyclooxygenase-1 and -2 expressed transiently in cos-1 cells, with the S530A mutant as a control
    exposure
    Valeryl salicylate and related esters compared with acetylsalicylate
    limitations
    Uses the acetylation chemistry as a design principle and confirms the serine requirement with a mutant. Recombinant enzyme and a murine fibroblast line, not human tissue.
    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 and sheep enzyme
    plain_language
    Swap aspirin’s acetyl group for a bigger one and you get a drug that hits only the first enzyme.
    primary_references
    [asa-p7872783] Selective inhibition of prostaglandin endoperoxide synthase-1 (cyclooxygenase-1) by valerylsalicylic acid. (1995). https://pubmed.ncbi.nlm.nih.gov/7872783/ DOI: 10.1006/abbi.1995.1130
    tissue_or_cell_type
    Recombinant cyclooxygenase

    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 182–193

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Eight acyl salicylates tested against human cyclooxygenase-1 and -2 expressed transiently in cos-1 cells, with the S530A mutant as a control · source_derived_draft · unverified_draft

    ### asa-bigger-acyl-group-selective Valeryl (pentanoyl) salicylate was the only compound of eight acyl salicylates to show isozyme selectivity and inhibited human cyclooxygenase-1 much more effectively than cyclooxygenase-2 in a time-dependent manner, inhibited ovine cyclooxygenase-1 but did not inhibit the S530A mutant of ovine cyclooxygenase-1 which is also refractory to acetylsalicylate, so valeryl salicylate acylates the active site serine. 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: Swap aspirin’s acetyl group for a bigger one and you get a drug that hits only the first enzyme. organism: Human and sheep enzyme tissue_or_cell_type: Recombinant cyclooxygenase experimental_model: Eight acyl salicylates tested against human cyclooxygenase-1 and -2 expressed transiently in cos-1 cells, with the S530A mutant as a control limitations: Uses the acetylation chemistry as a design principle and confirms the serine requirement with a mutant. Recombinant enzyme and a murine fibroblast line, not human tissue. exposure: Valeryl salicylate and related esters compared with acetylsalicylate evidence_span: {"source_cache": "artifacts/aspirin-research/7872783.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "f7e8a07a2704cb600938505ec51355671355769c01868ed0966731382901425b", "start_char": 0, "end_char": 1756, "text_sha256": "f7e8a07a2704cb600938505ec51355671355769c01868ed0966731382901425b"} [asa-p7872783] Selective inhibition of prostaglandin endoperoxide synthase-1 (cyclooxygenase-1) by valerylsalicylic acid. (1995). https://pubmed.ncbi.nlm.nih.gov/7872783/ DOI: 10.1006/abbi.1995.1130
    Complete structured claim and evidence

  2. Aspirin maximally acetylates one monomer of human cyclooxygenase-2, the acetylated monomer forming 15-hydroperoxyeicosatetraenoic acid from arachidonic acid while the nonacetylated partner monomer forms mainly prostaglandin H2 but at only 15 to 20% of the rate of native enzyme, conclusions based on diclofenac binding a single monomer of native enzyme having an unmodified Ser530 and on diclofenac inhibiting prostaglandin H2 but not 15-hydroperoxyeicosatetraenoic acid formation by the acetylated enzyme.

    Aspirin / acetylsalicylic acid → The cyclooxygenase-2 homodimer source_derived_draftungraded
    Experimental context and source evidence
    evidence_span
    {"source_cache": "artifacts/aspirin-research/20194532.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "09427e18078449741ea9ea42dc91a16f50ca9f604ec05c4decbb255731104eaf", "start_char": 0, "end_char": 1441, "text_sha256": "09427e18078449741ea9ea42dc91a16f50ca9f604ec05c4decbb255731104eaf"}
    experimental_model
    Quantitative characterisation of aspirin-acetylated human cyclooxygenase-2 monomers using diclofenac to distinguish them
    exposure
    Aspirin acetylation with arachidonic, eicosapentaenoic and docosahexaenoic acid as substrates
    limitations
    Measures rates rather than presence, and reaches a much less generous estimate of resolvin formation than the reports it tests. It is an in vitro enzyme study, so it does not exclude accumulation or amplification in a living tissue.
    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 enzyme
    plain_language
    Aspirin only ever modifies half of the paired enzyme, and the untouched half carries on at a fifth speed.
    primary_references
    [asa-p20194532] Asymmetric acetylation of the cyclooxygenase-2 homodimer by aspirin and its effects on the oxygenation of arachidonic, eicosapentaenoic, and docosahexaenoic acids. (2010). https://pubmed.ncbi.nlm.nih.gov/20194532/ DOI: 10.1124/mol.109.063115
    tissue_or_cell_type
    Cyclooxygenase-2 homodimer

    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 325–336

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Quantitative characterisation of aspirin-acetylated human cyclooxygenase-2 monomers using diclofenac to distinguish them · source_derived_draft · unverified_draft

    ### asa-only-one-monomer-is-acetylated Aspirin maximally acetylates one monomer of human cyclooxygenase-2, the acetylated monomer forming 15-hydroperoxyeicosatetraenoic acid from arachidonic acid while the nonacetylated partner monomer forms mainly prostaglandin H2 but at only 15 to 20% of the rate of native enzyme, conclusions based on diclofenac binding a single monomer of native enzyme having an unmodified Ser530 and on diclofenac inhibiting prostaglandin H2 but not 15-hydroperoxyeicosatetraenoic acid formation by the acetylated enzyme. 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: Aspirin only ever modifies half of the paired enzyme, and the untouched half carries on at a fifth speed. organism: Human enzyme tissue_or_cell_type: Cyclooxygenase-2 homodimer experimental_model: Quantitative characterisation of aspirin-acetylated human cyclooxygenase-2 monomers using diclofenac to distinguish them limitations: Measures rates rather than presence, and reaches a much less generous estimate of resolvin formation than the reports it tests. It is an in vitro enzyme study, so it does not exclude accumulation or amplification in a living tissue. exposure: Aspirin acetylation with arachidonic, eicosapentaenoic and docosahexaenoic acid as substrates evidence_span: {"source_cache": "artifacts/aspirin-research/20194532.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "09427e18078449741ea9ea42dc91a16f50ca9f604ec05c4decbb255731104eaf", "start_char": 0, "end_char": 1441, "text_sha256": "09427e18078449741ea9ea42dc91a16f50ca9f604ec05c4decbb255731104eaf"} [asa-p20194532] Asymmetric acetylation of the cyclooxygenase-2 homodimer by aspirin and its effects on the oxygenation of arachidonic, eicosapentaenoic, and docosahexaenoic acids. (2010). https://pubmed.ncbi.nlm.nih.gov/20194532/ DOI: 10.1124/mol.109.063115
    Complete structured claim and evidence

  3. When microsomal human cyclooxygenase-2 was incubated with acetyl-carbon-14 labelled aspirin the enzyme was acetylated, while an S516A mutant which retains enzyme activity was not acetylated, indicating that Ser-516 is the site of aspirin acetylation and is homologous to the active site serine of cyclooxygenase-1; an S516N mutant was catalytically active whereas an S516Q mutant lacked cyclooxygenase but retained peroxidase activity, and because in cyclooxygenase-1 the smaller asparagine substitution suffices to eliminate cyclooxygenase activity the active site of cyclooxygenase-2 is slightly larger.

    Aspirin / acetylsalicylic acid → Serine 516 of cyclooxygenase-2 source_derived_draftungraded
    Experimental context and source evidence
    evidence_span
    {"source_cache": "artifacts/aspirin-research/8175750.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "9ba85af90c62b157cf53032375ca703e8b78eff6ddd22ad627bbd7e65965d8e9", "start_char": 0, "end_char": 1786, "text_sha256": "9ba85af90c62b157cf53032375ca703e8b78eff6ddd22ad627bbd7e65965d8e9"}
    experimental_model
    Human cyclooxygenase-1 and -2 expressed in cos-1 cells treated with aspirin and with carbon-14 labelled aspirin, with a mutant series at Ser-516
    exposure
    Aspirin acetylation, with S516A, S516N, S516Q and S516M substitutions
    limitations
    Identifies the site by direct labelling and explains the isoform difference by active site volume. Recombinant enzyme in a heterologous cell line.
    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 enzyme
    plain_language
    The labelled acetyl group lands on one serine, and the second enzyme’s pocket is roomier, which is why the two behave differently.
    primary_references
    [asa-p8175750] Acetylation of human prostaglandin endoperoxide synthase-2 (cyclooxygenase-2) by aspirin. (1994). https://pubmed.ncbi.nlm.nih.gov/8175750/ DOI: 10.1016/s0021-9258(17)36820-5
    tissue_or_cell_type
    Recombinant cyclooxygenase

    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 221–232

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Human cyclooxygenase-1 and -2 expressed in cos-1 cells treated with aspirin and with carbon-14 labelled aspirin, with a mutant series at Ser-516 · source_derived_draft · unverified_draft

    ### asa-ser516-is-the-site When microsomal human cyclooxygenase-2 was incubated with acetyl-carbon-14 labelled aspirin the enzyme was acetylated, while an S516A mutant which retains enzyme activity was not acetylated, indicating that Ser-516 is the site of aspirin acetylation and is homologous to the active site serine of cyclooxygenase-1; an S516N mutant was catalytically active whereas an S516Q mutant lacked cyclooxygenase but retained peroxidase activity, and because in cyclooxygenase-1 the smaller asparagine substitution suffices to eliminate cyclooxygenase activity the active site of cyclooxygenase-2 is slightly larger. 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 labelled acetyl group lands on one serine, and the second enzyme’s pocket is roomier, which is why the two behave differently. organism: Human enzyme tissue_or_cell_type: Recombinant cyclooxygenase experimental_model: Human cyclooxygenase-1 and -2 expressed in cos-1 cells treated with aspirin and with carbon-14 labelled aspirin, with a mutant series at Ser-516 limitations: Identifies the site by direct labelling and explains the isoform difference by active site volume. Recombinant enzyme in a heterologous cell line. exposure: Aspirin acetylation, with S516A, S516N, S516Q and S516M substitutions evidence_span: {"source_cache": "artifacts/aspirin-research/8175750.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "9ba85af90c62b157cf53032375ca703e8b78eff6ddd22ad627bbd7e65965d8e9", "start_char": 0, "end_char": 1786, "text_sha256": "9ba85af90c62b157cf53032375ca703e8b78eff6ddd22ad627bbd7e65965d8e9"} [asa-p8175750] Acetylation of human prostaglandin endoperoxide synthase-2 (cyclooxygenase-2) by aspirin. (1994). https://pubmed.ncbi.nlm.nih.gov/8175750/ DOI: 10.1016/s0021-9258(17)36820-5
    Complete structured claim and evidence

  4. Cos-1 cells transfected with native or Ser-530-to-alanine mutant sheep prostaglandin endoperoxide synthase expressed comparable cyclooxygenase and hydroperoxidase activities, with the same Km for arachidonate of 8 micromolar and the same ID50 values for reversible inhibition by flurbiprofen at 5 micromolar, flufenamate at 20 micromolar and aspirin at 20 millimolar; however only the native enzyme was irreversibly inactivated by aspirin, so the active site Ser-530 is not essential for catalysis or substrate binding.

    Cyclooxygenase-1 with alanine substituted at position 530 → The cyclooxygenase activity of prostaglandin endoperoxide synthase source_derived_draftungraded
    Experimental context and source evidence
    evidence_span
    {"source_cache": "artifacts/aspirin-research/2108169.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "c7b11508521a3854b432f3836de6e92ba9863c8edb244d747bb1c37634c0bb50", "start_char": 0, "end_char": 2076, "text_sha256": "c7b11508521a3854b432f3836de6e92ba9863c8edb244d747bb1c37634c0bb50"}
    experimental_model
    Site-directed mutagenesis of sheep prostaglandin endoperoxide synthase expressed in Cos-1 cells
    exposure
    Serine 530 replaced with alanine, compared with the native enzyme against aspirin and reversible inhibitors
    limitations
    The decisive experiment for the mechanism: it separates what the serine does for catalysis from what acetylating it does. Recombinant sheep enzyme, not human enzyme in a tissue.
    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
    Sheep and mouse enzyme
    plain_language
    Remove the serine and the enzyme still works; it is there to be acetylated, not to do the chemistry.
    primary_references
    [asa-p2108169] The aspirin and heme-binding sites of ovine and murine prostaglandin endoperoxide synthases. (1990). https://pubmed.ncbi.nlm.nih.gov/2108169/ DOI: 10.1016/s0021-9258(19)34105-5
    tissue_or_cell_type
    Recombinant enzyme in Cos-1 cells

    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 78–89

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Site-directed mutagenesis of sheep prostaglandin endoperoxide synthase expressed in Cos-1 cells · source_derived_draft · unverified_draft

    ### asa-serine-is-not-catalytic Cos-1 cells transfected with native or Ser-530-to-alanine mutant sheep prostaglandin endoperoxide synthase expressed comparable cyclooxygenase and hydroperoxidase activities, with the same Km for arachidonate of 8 micromolar and the same ID50 values for reversible inhibition by flurbiprofen at 5 micromolar, flufenamate at 20 micromolar and aspirin at 20 millimolar; however only the native enzyme was irreversibly inactivated by aspirin, so the active site Ser-530 is not essential for catalysis or substrate binding. 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: Remove the serine and the enzyme still works; it is there to be acetylated, not to do the chemistry. organism: Sheep and mouse enzyme tissue_or_cell_type: Recombinant enzyme in Cos-1 cells experimental_model: Site-directed mutagenesis of sheep prostaglandin endoperoxide synthase expressed in Cos-1 cells limitations: The decisive experiment for the mechanism: it separates what the serine does for catalysis from what acetylating it does. Recombinant sheep enzyme, not human enzyme in a tissue. exposure: Serine 530 replaced with alanine, compared with the native enzyme against aspirin and reversible inhibitors evidence_span: {"source_cache": "artifacts/aspirin-research/2108169.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "c7b11508521a3854b432f3836de6e92ba9863c8edb244d747bb1c37634c0bb50", "start_char": 0, "end_char": 2076, "text_sha256": "c7b11508521a3854b432f3836de6e92ba9863c8edb244d747bb1c37634c0bb50"} [asa-p2108169] The aspirin and heme-binding sites of ovine and murine prostaglandin endoperoxide synthases. (1990). https://pubmed.ncbi.nlm.nih.gov/2108169/ DOI: 10.1016/s0021-9258(19)34105-5
    Complete structured claim and evidence

  5. 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

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