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Key Event: 1767

Key Event Title

A descriptive phrase which defines a discrete biological change that can be measured. More help

Increase, Protein oxidation

Short name

The KE short name should be a reasonable abbreviation of the KE title and is used in labelling this object throughout the AOP-Wiki. More help

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Biological Context

Structured terms, selected from a drop-down menu, are used to identify the level of biological organization for each KE. More help

Level of Biological Organization
Molecular

Cell term

The location/biological environment in which the event takes place.The biological context describes the location/biological environment in which the event takes place. For molecular/cellular events this would include the cellular context (if known), organ context, and species/life stage/sex for which the event is relevant. For tissue/organ events cellular context is not applicable. For individual/population events, the organ context is not applicable. Further information on Event Components and Biological Context may be viewed on the attached pdf. More help

Cell term
cell

Organ term

Organ term
organ

Event Components

The KE, as defined by a set structured ontology terms consisting of a biological process, object, and action with each term originating from one of 14 biological ontologies (Ives, et al., 2017; https://aopwiki.org/info_pages/2/info_linked_pages/7#List). Biological process describes dynamics of the underlying biological system (e.g., receptor signalling).Biological process describes dynamics of the underlying biological system (e.g., receptor signaling). The biological object is the subject of the perturbation (e.g., a specific biological receptor that is activated or inhibited). Action represents the direction of perturbation of this system (generally increased or decreased; e.g., ‘decreased’ in the case of a receptor that is inhibited to indicate a decrease in the signaling by that receptor). Note that when editing Event Components, clicking an existing Event Component from the Suggestions menu will autopopulate these fields, along with their source ID and description. To clear any fields before submitting the event component, use the 'Clear process,' 'Clear object,' or 'Clear action' buttons. If a desired term does not exist, a new term request may be made via Term Requests. Event components may not be edited; to edit an event component, remove the existing event component and create a new one using the terms that you wish to add. Further information on Event Components and Biological Context may be viewed on the attached pdf. More help

Process	Object	Action
protein oxidation		increased

Key Event Overview

AOPs Including This Key Event

All of the AOPs that are linked to this KE will automatically be listed in this subsection. This table can be particularly useful for derivation of AOP networks including the KE.Clicking on the name of the AOP will bring you to the individual page for that AOP. More help

AOP Name	Role of event in AOP	Point of Contact	Author Status
Excessive ROS leading to mortality (1)	KeyEvent	You Song (send email)	Under development: Not open for comment. Do not cite
ROS leading to growth inhibition via protein oxidation and cell injury/death	KeyEvent	You Song (send email)	Under development: Not open for comment. Do not cite
ROS leading to growth inhibition via protein oxidation and reduced cell proliferation	KeyEvent	You Song (send email)	Under development: Not open for comment. Do not cite
ROS leading to growth inhibition via fatty acid oxidation and cell injury/death	KeyEvent	You Song (send email)	Under development: Not open for comment. Do not cite
ROS leading to growth inhibition via fatty acid oxidation and reduced cell growth	KeyEvent	You Song (send email)	Under development: Not open for comment. Do not cite
ROS leading to growth inhibition via fatty acid oxidation and reduced cell proliferation	KeyEvent	You Song (send email)	Under development: Not open for comment. Do not cite
ROS leading to growth inhibition via protein oxidation and cell cycle disruption	KeyEvent	You Song (send email)	Under development: Not open for comment. Do not cite
ROS leading to growth inhibition via protein oxidation and decreased cell proliferation	KeyEvent	You Song (send email)	Under development: Not open for comment. Do not cite
ROS leading to growth inhibition via protein oxidation and cell death	KeyEvent	You Song (send email)	Under development: Not open for comment. Do not cite

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) that help to define the biological applicability domain of the KE.In many cases, individual species identified in these structured fields will be those for which the strongest evidence used in constructing the AOP was available in relation to this KE. More help

Term	Scientific Term	Evidence	Link
humans	Homo sapiens	High	NCBI
mammals	mammals	High	NCBI
fish	fish	High	NCBI
crustaceans	Daphnia magna	Moderate	NCBI
green algae	Ulva compressa	Moderate	NCBI

Life Stages

An indication of the the relevant life stage(s) for this KE. More help

Life stage	Evidence
All life stages	Moderate

Sex Applicability

An indication of the the relevant sex for this KE. More help

Term	Evidence
Unspecific	Moderate

Key Event Description

A description of the biological state being observed or measured, the biological compartment in which it is measured, and its general role in the biology should be provided. More help

Protein oxidation refers to an increase in oxidative modification of proteins relative to an appropriate control state. Proteins are abundant and chemically diverse macromolecules that contain amino-acid side chains and peptide backbones susceptible to attack by ROS and related oxidants. Oxidation can lead to formation of protein carbonyls, oxidation of sulfur-containing amino acids such as cysteine and methionine, nitration or hydroxylation of aromatic residues, disulfide formation, S-glutathionylation, fragmentation, cross-linking, aggregation, altered folding and changes in enzymatic or structural function (Stadtman and Levine, 2003; Dalle-Donne et al., 2006; Fedorova et al., 2014).

The KE is defined by the observed or measured increase in oxidatively modified proteins rather than by a particular upstream stressor or downstream consequence. Protein oxidation can be reversible or irreversible depending on the chemical modification. Reversible thiol oxidation, disulfide formation, S-glutathionylation and methionine oxidation may participate in redox signaling and adaptive regulation, whereas irreversible carbonylation, backbone cleavage and protein aggregation are more commonly associated with protein dysfunction, proteostatic burden and cellular injury (Stadtman and Levine, 2003; Dalle-Donne et al., 2006; Reichmann et al., 2018).

Within oxidative stress AOPs, protein oxidation is an important molecular damage KE because it links redox imbalance to functional impairment of enzymes, structural proteins, signaling proteins and organelle proteins. In the ROS-growth AOP network, oxidation of mitochondrial respiratory proteins, cytoskeletal proteins or metabolic enzymes may contribute to decreased coupling of oxidative phosphorylation, impaired ATP production, altered cell cycle regulation, increased cell injury/death and reduced growth. However, these downstream consequences should be described on separate KER and AOP pages so that KE 1767 remains modular and reusable.

How It Is Measured or Detected

A description of the type(s) of measurements that can be employed to evaluate the KE and the relative level of scientific confidence in those measurements.These can range from citation of specific validated test guidelines, citation of specific methods published in the peer reviewed literature, or outlines of a general protocol or approach (e.g., a protein may be measured by ELISA). Do not provide detailed protocols. More help

Protein oxidation can be measured using biochemical, immunochemical, fluorescence-based and proteomic approaches. No single method captures all forms of protein oxidation. Protein carbonylation is one of the most widely used and relatively stable indicators of oxidative protein damage, but other modifications such as methionine sulfoxide, cysteine oxidation, nitrotyrosine, S-glutathionylation and protein cross-linking may be more appropriate in particular biological contexts. Confidence is highest when the method directly detects a defined oxidized protein modification or oxidized peptide, and lower when broad assays are used without complementary specificity checks.

Measurement approach	Endpoint measured	Representative method names	Scientific confidence and limitations
Protein carbonyl assays	Protein carbonyl groups formed by direct oxidation or by adduction of reactive carbonyl species	DNPH derivatization with spectrophotometry, ELISA, immunoblotting or OxyBlot; hydrazide-based probes	Widely used, relatively stable and broadly accepted as a marker of protein oxidation. DNPH methods are sensitive but do not identify individual proteins unless combined with immunoblotting or proteomics. Carbonyls may arise from direct oxidation or from secondary reactions with lipid peroxidation products (Levine et al., 1990; Dalle-Donne et al., 2006; Fedorova et al., 2014).
Redox proteomics	Oxidized proteins or oxidized amino-acid residues at protein or peptide level	2D gel electrophoresis plus anti-DNP immunoblotting; LC-MS/MS redox proteomics; carbonyl-reactive enrichment workflows	High mechanistic value because it can identify protein targets and modification sites. Requires careful sample handling, derivatization or enrichment, and appropriate bioinformatic analysis (McDonagh et al., 2005; Fedorova et al., 2014; Butterfield and Dalle-Donne, 2014).
Thiol oxidation assays	Oxidation state of protein thiols and disulfides	Biotin-switch methods; maleimide labeling; redox Western blot; differential alkylation; thiol redox proteomics	Useful for reversible cysteine oxidation and redox signaling. Interpretation depends on preservation of redox state during sampling and on whether reversible signaling events or irreversible damage are being assessed (Dalle-Donne et al., 2006; Reichmann et al., 2018).
S-glutathionylation assays	Protein S-glutathionylation as a reversible thiol redox modification	Anti-glutathione immunoblotting; redox proteomics; mass spectrometry	Mechanistically informative for redox regulation and oxidative stress responses. It may represent adaptive regulation rather than irreversible damage and should be interpreted in biological context (Dailianis et al., 2009; Zaffagnini et al., 2012).
Nitrotyrosine and other specific oxidized residue assays	Specific oxidized or nitrated amino-acid residues	Anti-nitrotyrosine immunoassays; LC-MS/MS; targeted proteomics	Provides higher chemical specificity for particular oxidant pathways, such as peroxynitrite-associated nitration, but does not capture all protein oxidation. Best used when the expected chemistry is known.
Advanced oxidation protein products and aggregate assays	Bulk oxidized protein products, cross-linked proteins or protein aggregates	AOPP assays; aggregate detection; protein insolubility assays	Useful for broad screening of oxidative protein burden but less specific than defined chemical or proteomic measurements. Should be interpreted as supportive evidence, especially when combined with carbonyl or mass-spectrometric endpoints.

Domain of Applicability

A description of the scientific basis for the indicated domains of applicability and the WoE calls (if provided). More help

The biological domain of applicability for this KE is broad because proteins are universal biological macromolecules and many amino-acid residues are susceptible to oxidative modification. The KE is applicable wherever proteins are exposed to oxidants and where oxidative modification can be measured. It is therefore relevant across unicellular algae, invertebrates, fish, mammals, plants and human-derived cell systems. The evidence base is strongest in mammalian toxicology and biomedical studies, but ecotoxicological evidence supports relevance in algae, fish, mollusks and crustaceans.

The KE is not intrinsically limited by life stage or sex. However, the magnitude and toxicological importance of protein oxidation may be modified by antioxidant capacity, proteasomal and lysosomal degradation capacity, protein turnover, metal ion availability, oxygen availability, temperature, inflammatory status, nutritional status, mitochondrial activity, and exposure duration. Tissues or cells with high metabolic demand, high mitochondrial density, high inflammatory activity, or low proteostatic reserve may be especially susceptible.

Within the ROS-growth AOP network, this KE functions as a molecular damage event linking oxidative stress to downstream impairment of mitochondrial function and cellular injury. Nevertheless, the KE should remain modular. It may be reused in any AOP in which increased oxidative modification of proteins is measured or inferred as a discrete biological state, regardless of whether the downstream effect is impaired oxidative phosphorylation, cell death, altered signaling, immune dysfunction, neurotoxicity, growth inhibition or another adverse outcome.

References

List of the literature that was cited for this KE description. More help

AOP-Wiki. 2026. Key Event 1767: Increase, Protein oxidation. AOP-Wiki. Available at: https://aopwiki.org/events/1767. Accessed 14 May 2026.

Almaida-Pagán PF, Lucas-Sánchez A, Tocher DR. 2014. Changes in mitochondrial membrane composition and oxidative status during rapid growth, maturation and aging in zebrafish, Danio rerio. Biochimica et Biophysica Acta - Molecular and Cell Biology of Lipids 1841(7):1003-1011. https://doi.org/10.1016/j.bbalip.2014.04.004.

Butterfield DA, Dalle-Donne I. 2014. Redox proteomics: from protein modifications to cellular dysfunction and diseases. Mass Spectrometry Reviews 33(1):1-6. https://doi.org/10.1002/mas.21382.

Dailianis S, Patetsini E, Kaloyianni M. 2009. The role of signaling molecules on actin glutathionylation and protein carbonylation induced by cadmium in hemocytes of mussel Mytilus galloprovincialis. Journal of Experimental Biology 212(22):3612-3620. https://doi.org/10.1242/jeb.031211.

Dalle-Donne I, Aldini G, Carini M, Colombo R, Rossi R, Milzani A. 2006. Protein carbonylation, cellular dysfunction, and disease progression. Journal of Cellular and Molecular Medicine 10(2):389-406. https://doi.org/10.1111/j.1582-4934.2006.tb00407.x.

Fedorova M, Bollineni RC, Hoffmann R. 2014. Protein carbonylation as a major hallmark of oxidative damage: update of analytical strategies. Mass Spectrometry Reviews 33(2):79-97. https://doi.org/10.1002/mas.21381.

Levine RL, Garland D, Oliver CN, Amici A, Climent I, Lenz AG, Ahn BW, Shaltiel S, Stadtman ER. 1990. Determination of carbonyl content in oxidatively modified proteins. Methods in Enzymology 186:464-478. https://doi.org/10.1016/0076-6879(90)86141-H.

Martínez M, Rodríguez-Graña L, Santos L, Denicola A, Calliari D. 2020. Long-term exposure to salinity variations induces protein carbonylation in the copepod Acartia tonsa. Journal of Experimental Marine Biology and Ecology 526:151337. https://doi.org/10.1016/j.jembe.2020.151337.

McDonagh B, Tyther R, Sheehan D. 2005. Carbonylation and glutathionylation of proteins in the blue mussel Mytilus edulis detected by proteomic analysis and Western blotting: actin as a target for oxidative stress. Aquatic Toxicology 73(3):315-326. https://doi.org/10.1016/j.aquatox.2005.03.020.

Mukherjee K, Chio TI, Sackett DL, Bane SL. 2015. Detection of oxidative stress-induced carbonylation in live mammalian cells using a hydrazine-based fluorescent probe. Free Radical Biology and Medicine 84:11-21. https://doi.org/10.1016/j.freeradbiomed.2015.03.011.

Parvez S, Raisuddin S. 2005. Protein carbonyls: novel biomarkers of exposure to oxidative stress-inducing pesticides in freshwater fish Channa punctata (Bloch). Environmental Toxicology and Pharmacology 20(1):112-117. https://doi.org/10.1016/j.etap.2004.11.002.

Reichmann D, Voth W, Jakob U. 2018. Maintaining a healthy proteome during oxidative stress. Molecular Cell 69(2):203-213. https://doi.org/10.1016/j.molcel.2017.12.021.

Sokolov EP, Markert S, Hinzke T, Hirschfeld C, Becher D, Ponsuksili S, Sokolova IM. 2019. Effects of hypoxia-reoxygenation stress on mitochondrial proteome and bioenergetics of the hypoxia-tolerant marine bivalve Crassostrea gigas. Journal of Proteomics 194:99-111. https://doi.org/10.1016/j.jprot.2018.12.009.

Stadtman ER, Levine RL. 2003. Free radical-mediated oxidation of free amino acids and amino acid residues in proteins. Amino Acids 25(3-4):207-218. https://doi.org/10.1007/s00726-003-0011-2.

Tseng YC, Chen RD, Lucassen M, Schmidt MM, Dringen R, Abele D, Hwang PP. 2011. Exploring uncoupling proteins and antioxidant mechanisms under acute cold exposure in brains of fish. PLoS ONE 6(3):e18180. https://doi.org/10.1371/journal.pone.0018180.

Zaffagnini M, Bedhomme M, Groni H, Marchand CH, Puppo C, Gontero B, Cassier-Chauvat C, Decottignies P, Lemaire SD. 2012. Glutathionylation in the photosynthetic model organism Chlamydomonas reinhardtii: a proteomic survey. Molecular & Cellular Proteomics 11(2):M111.014142. https://doi.org/10.1074/mcp.M111.014142.