Cellular Peroxide-Scavenging Enzyme Systems: Functional Division of Glutathione Peroxidase, Catalase, and Peroxiredoxin

Intracellular H₂O₂ and lipid peroxides require the coordinated action of multiple antioxidant enzyme systems for clearance. Among them, Glutathione Peroxidase (GPx), Catalase (CAT), and Peroxiredoxin (PRDX) control peroxides in different substrate and subcellular environments. GPX4 further links glutathione metabolism, lipid peroxidation, and ferroptosis regulation by reducing membrane phospholipid peroxides.

Keywords: Glutathione Peroxidase; GPX4; glutathione; Catalase; Peroxiredoxin; lipid peroxidation; ferroptosis

1 Cellular Peroxide-Scavenging Systems

1.1 Major Sources of Peroxides

Mitochondrial electron transport, NADPH oxidase, peroxisomal fatty acid oxidation, and multiple oxidase reactions can all generate Reactive Oxygen Species (ROS). Superoxide (O₂•⁻) is dismutated by Superoxide Dismutase (SOD) to generate H₂O₂. At appropriate levels, H₂O₂ participates in redox signaling, whereas excessive accumulation can cause oxidation of proteins, lipids, and nucleic acids. Therefore, the balance between its generation rate and scavenging capacity is critical for maintaining cellular redox homeostasis.

1.2 Functional Classification of Peroxide-Scavenging Enzymes

(1) Glutathione-Dependent Peroxide Scavenging

Classical GSH-dependent GPx enzymes use reduced glutathione (GSH) as a reducing donor to reduce H₂O₂ or organic peroxides while generating oxidized glutathione (GSSG), whereas nonclassical members such as GPX7 and GPX8 have distinct reductive and catalytic mechanisms. Different GPx members vary in substrate type, tissue distribution, and subcellular localization, among which GPX4 is capable of directly reducing membrane phospholipid hydroperoxides.

(2) High-Capacity H₂O₂ Scavenging by Catalase

CAT can directly decompose H₂O₂ into H₂O and O₂ without requiring GSH or Thioredoxin as reducing substrates. Its high catalytic capacity makes it suitable for limiting large amounts of H₂O₂, particularly in relation to H₂O₂ metabolism in peroxisomes.

(3) Peroxiredoxin-Dependent Local Scavenging

Most canonical PRDX proteins use active Cysteine residues to reduce H₂O₂ and some organic peroxides and are restored through the Thioredoxin system, whereas PRDX6 is a 1-Cys PRDX whose reductive cycle primarily involves the GSH/GSTπ system. PRDX participates not only in antioxidant defense but also in regulation of local H₂O₂ concentrations and redox signaling.

Table 1 Major Peroxide-Scavenging Enzyme Systems

Enzyme System	Major Reducing System	Typical Substrates	Major Functional Positioning
GPx	GSH/GSSG	H₂O₂, organic peroxides, some lipid peroxides	GSH-dependent peroxide scavenging
CAT	GSH-independent	H₂O₂	High-capacity H₂O₂ decomposition
PRDX	Thioredoxin system	H₂O₂, some organic peroxides	Local peroxide scavenging and redox signaling
GPX4	GSH/GSSG	Phospholipid hydroperoxides	Membrane lipid protection and ferroptosis suppression

2 Glutathione Peroxidase Family

2.1 GPx Catalytic Cycle

Classical GSH-dependent GPx enzymes consume GSH during peroxide reduction and generate GSSG. Glutathione Reductase (GR) subsequently uses NADPH to reduce GSSG back to GSH. The GSH–GPx–GR cycle therefore directly links peroxide-scavenging capacity with cellular glutathione reserves, GR activity, and NADPH supply. Limitation at any one of these steps can reduce overall GPx antioxidant capacity.

2.2 GPX1

GPX1 is a widely expressed intracellular GPx member that mainly participates in the clearance of H₂O₂ and some soluble organic peroxides. Reduced GPX1 activity can increase cellular sensitivity to oxidative stimulation and is therefore commonly used to evaluate overall GSH-dependent antioxidant defense, selenoprotein function, and oxidative stress status.

2.3 GPX2

GPX2 is prominently expressed in tissues such as the gastrointestinal epithelium and participates in peroxide clearance and maintenance of redox homeostasis in epithelial cells. Its research commonly involves intestinal barriers, inflammation, epithelial renewal, and tumor-related oxidative stress, giving it a tissue-localization profile distinct from the broadly expressed GPX1.

2.4 GPX3

GPX3 is a major extracellular secreted GPx member and can be present in plasma and other extracellular environments. Its function is more focused on extracellular peroxide control and systemic redox status, making it valuable in studies of circulating oxidative stress, vascular environments, and inter-tissue antioxidant defense.

2.5 GPX4

(1) Substrate Specificity

GPX4, also known as Phospholipid Hydroperoxide Glutathione Peroxidase, is distinguished by its ability to directly reduce lipid hydroperoxides within membrane phospholipids. Compared with antioxidant enzymes that mainly process water-soluble H₂O₂, GPX4 directly acts on membrane lipid oxidation products and is an important enzyme for limiting lipid radical chain reactions.

(2) Membrane Lipid Protection

Membrane phospholipids containing Polyunsaturated Fatty Acids are susceptible to radical oxidation and formation of Phospholipid Hydroperoxides. GPX4 uses GSH to reduce these oxidized phospholipids into the corresponding lipid alcohols, thereby reducing membrane damage and propagation of lipid radicals.

(3) Ferroptosis Regulation

When GPX4 function is reduced, membrane phospholipid peroxides continue to accumulate and promote lipid radical chain reactions. When this damage exceeds cellular antioxidant capacity, Ferroptosis-related membrane oxidative injury can occur. GPX4 is therefore one of the core nodes of the ferroptosis defense system.

2.6 Other GPx Members

GPX5, GPX6, GPX7, and GPX8 have distinct tissue distributions, catalytic mechanisms, and subcellular localizations. GPX7 and GPX8 are associated with the endoplasmic reticulum redox environment and protein-folding processes. The GPx family is therefore not simply a collection of H₂O₂-scavenging enzymes but a redox-regulatory system with clear tissue and organelle specificity.

Table 2 Functional Differences Among Major GPx Members

GPx Member	Major Localization or Characteristics	Major Function
GPX1	Broad intracellular expression	Clearance of H₂O₂ and soluble peroxides
GPX2	Prominent expression in gastrointestinal epithelium	Epithelial redox homeostasis
GPX3	Secreted, extracellular	Extracellular peroxide scavenging
GPX4	Membranes and multiple subcellular regions	Phospholipid peroxide reduction and ferroptosis suppression
GPX5	Reproductive system-related expression	Local oxidative stress defense
GPX7/8	Endoplasmic reticulum-related	Protein folding and local redox regulation

3 Selenium and GPx Activity

3.1 Selenium-Dependent GPx

Classical members including GPX1, GPX3, and GPX4 are important selenoproteins whose active centers contain Selenocysteine (Sec). Sec has high redox reactivity, enabling these GPx enzymes to efficiently catalyze peroxide reduction. Therefore, selenium availability can affect synthesis and antioxidant function of some GPx proteins.

3.2 Selenium Status and Evaluation of GPx Function

Insufficient selenium supply may limit selenoprotein synthesis and reduce the activity of some GPx enzymes. Experiments should separately evaluate GPx protein expression, enzyme activity, and cellular GSH status because reduced GPx activity may result from insufficient protein levels or from GSH deficiency, limited NADPH supply, or oxidative inactivation of the active center.

4 H₂O₂-Scavenging Function of Catalase

4.1 Catalytic Characteristics

Catalase is a Heme-containing antioxidant enzyme that catalyzes conversion of H₂O₂ into H₂O and O₂. CAT does not require consumption of GSH and therefore forms a peroxide-scavenging mode distinct from GPx, particularly suitable for processing high fluxes of H₂O₂.

4.2 Peroxisomal Localization

In mammals, CAT is mainly localized in the Peroxisome, which is also an important site of fatty acid oxidation and H₂O₂ generation. CAT provides a high-capacity scavenging mechanism close to the site of ROS generation, limiting H₂O₂ diffusion into the cytoplasm and reducing secondary oxidative damage.

4.3 Functional Differences Between CAT and GPx

CAT is more oriented toward high-capacity decomposition of H₂O₂, whereas GPx can cover H₂O₂ and some organic peroxides and is directly coupled to GSH metabolism. GPX4 additionally has substrate specificity for membrane phospholipid peroxides. CAT and GPx therefore have complementary rather than simply interchangeable functions.

5 Peroxiredoxin and Redox Signaling

5.1 PRDX Catalytic Mechanism

In canonical 2-Cys PRDX proteins, the Peroxidatic Cysteine first reacts with peroxides, followed by a catalytic cycle involving the Resolving Cysteine and the Thioredoxin system; PRDX6 lacks the canonical Resolving Cysteine and uses a distinct reductive mechanism. This mechanism gives PRDX high reactivity toward H₂O₂ and allows it to participate in fine redox regulation at relatively low peroxide levels.

5.2 PRDX Family

Mammals mainly contain PRDX1–PRDX6, with different members having different subcellular localizations. PRDX1 and PRDX2 are mainly cytoplasmic, PRDX3 is predominantly localized in mitochondria, PRDX4 is associated with the endoplasmic reticulum and secretory pathway, and PRDX6 has catalytic characteristics different from typical 2-Cys PRDX proteins.

5.3 H₂O₂ Signal Regulation

PRDX not only performs H₂O₂-scavenging functions but also participates in formation of local redox signals. Under relatively strong oxidative conditions, some PRDX proteins can undergo hyperoxidation and temporarily lose peroxidase activity, thereby altering local H₂O₂ levels and downstream protein oxidation states.

6 Functional Division Among GPx, CAT, and PRDX

6.1 H₂O₂ Control

CAT, GPx, and PRDX can all participate in H₂O₂ clearance, but they differ in catalytic capacity, reducing systems, and subcellular localization. CAT is suitable for high-flux H₂O₂ decomposition, PRDX is highly responsive to low-level local H₂O₂, and GPx directly connects peroxide clearance with the GSH/GSSG redox cycle.

6.2 Organic Peroxide Control

GPx and some PRDX members can process organic peroxides. Therefore, when tert-Butyl Hydroperoxide (tBHP) or Cumene Hydroperoxide is used to establish oxidative models, the status of GPx, PRDX, GSH, and other antioxidant systems needs to be considered simultaneously. CAT activity alone cannot fully represent organic peroxide-scavenging capacity.

6.3 Lipid Peroxide Control

Membrane phospholipid peroxides require antioxidant systems with greater substrate specificity, among which GPX4 has a core role. Even when total H₂O₂ or total ROS does not increase significantly, impaired GPX4 function can still cause persistent accumulation of membrane lipid peroxides. Total ROS and lipid ROS therefore represent different levels of oxidative stress readouts.

Table 3 Functional Division Among GPx, CAT, and PRDX

Characteristic	GPx	CAT	PRDX
Major reducing system	GSH/GR/NADPH	GSH-independent	Trx/TrxR/NADPH
H₂O₂ scavenging	Yes	Yes	Yes
Organic peroxides	Strong in some members	Relatively limited	Some members
Membrane phospholipid peroxides	Prominent for GPX4	Limited	Limited
Major research value	GSH-dependent antioxidation, ferroptosis	High-capacity H₂O₂ scavenging	ROS signaling and local redox regulation
Typical abnormality	GSH depletion, lipid peroxidation	H₂O₂ accumulation	Local redox imbalance

7 GPX4 and Ferroptosis

7.1 GSH–GPX4 Defense Axis

GPX4 uses GSH to reduce Phospholipid Hydroperoxides into the corresponding lipid alcohols, thereby interrupting membrane lipid radical chain reactions. Cellular GSH is mainly maintained through Cystine/Cysteine supply and glutathione synthesis pathways. System Xc⁻, GSH synthesis, and GPX4 therefore jointly constitute an important Ferroptosis defense axis.

7.2 GPX4 Functional Inhibition

Compounds such as RSL3 can inhibit GPX4 function, whereas Erastin-related treatments can indirectly weaken GPX4 antioxidant capacity by limiting Cystine utilization and reducing GSH supply. After GPX4 defense fails, PUFA-containing membrane phospholipid peroxides continuously accumulate and produce progressive membrane damage in an iron-dependent oxidative environment.

7.3 Interpretation of Ferroptosis

Ferroptosis cannot be determined solely from increased total ROS or reduced cell viability. A more complete experimental evaluation should combine GPX4, GSH/GSSG, lipid peroxidation, iron dependence, and rescue effects of lipid-radical-trapping agents such as Ferrostatin-1 or Liproxstatin-1 to distinguish ferroptosis from other forms of oxidative stress-related cell death.

8 Experimental Evaluation of Peroxide-Scavenging Systems

8.1 GPx Activity Detection

GPx activity can be evaluated using the DTNB method or an NADPH-coupled rate method. In the NADPH-coupled system, GR reduces GSSG generated by the GPx reaction back to GSH while simultaneously consuming NADPH. Therefore, the rate of decrease in absorbance at 340 nm can indirectly reflect GPx catalytic activity.

8.2 GSH/GSSG Status

GSH content, GSSG levels, and the GSH/GSSG ratio are used to evaluate cellular glutathione redox status but cannot replace GPx activity measurements. Reduced GSH can result from insufficient synthesis, increased oxidative consumption, or impaired regeneration and therefore needs to be interpreted together with GR, NADPH, and GPx-related readouts.

8.3 CAT and PRDX Evaluation

CAT studies can directly measure enzyme activity and protein levels, whereas PRDX studies can combine total protein, oxidation status, and subcellular localization. Because PRDX participates in low-level H₂O₂ signaling regulation, relying solely on total ROS changes may fail to reflect its local functional alterations.

8.4 Lipid Peroxidation Evaluation

GPX4 studies should emphasize lipid-specific oxidative indicators, including lipid ROS, MDA, 4-HNE, and other oxidized lipid readouts. The absence of a significant increase in total ROS does not exclude membrane lipid peroxidation. Lipid-level indicators therefore have more direct interpretive value in Ferroptosis and GPX4 functional research.

9 Interpretation of Common Results

9.1 Reduced GPx Activity With Stable Protein Expression

When GPx protein levels remain largely stable but enzyme activity decreases, analysis should focus on GSH availability, Selenium status, the NADPH/GR cycle, and oxidation of the enzyme active center. This result generally indicates abnormal GPx functional status and cannot be directly attributed to insufficient protein expression.

9.2 Reduced GSH With Enhanced Lipid Peroxidation

Marked GSH depletion accompanied by reduced GPX4 function and increased lipid peroxidation suggests impairment of the GSH–GPX4 defense axis. If Ferrostatin-1 or Liproxstatin-1 markedly reduces the damage, this further supports the involvement of lipid radical chain reactions and Ferroptosis.

9.3 Reduced CAT With Increased GPx or PRDX

Reduced CAT activity accompanied by increased GPx or PRDX expression may reflect compensation within the antioxidant system, but it cannot be used to conclude that cellular redox homeostasis has been restored. Different antioxidant enzymes have different substrate ranges and subcellular localizations, and compensatory increases cannot completely replace the original enzyme-system function.

10 Products Related to Peroxide Scavenging and GPX4 Research

10.1 Glutathione Peroxidase-Related Products

Catalog #	Product Name	Grade & Purity	Research Positioning
rp192119	Recombinant Human Glutathione Peroxidase 1/GPX1 Protein	Carrier Free, His Tag, ≥90% (SDS-PAGE), expressed in E. coli; See COA	GPX1 protein and enzymatic function research
Ab105715	Recombinant Glutathione Peroxidase 2/GPX2 Antibody	Recombinant, ExactAb™, Validated, See COA	GPX2 expression and epithelial antioxidant research
Ab105733	Recombinant Glutathione Peroxidase 4 Antibody	Recombinant, ExactAb™, Validated, 0.5 mg/mL	GPX4 expression and ferroptosis research
Ab327014	Recombinant Glutathione Peroxidase 4 Antibody	KD Validation	GPX4 protein detection in cells and tissues
EJ1514953	Human Glutathione Peroxidase 1 (GPX1) ELISA Kit	BioReagent	Human GPX1 quantification
G1505763	Glutathione Peroxidase (GSH-Px) Activity Assay Kit (DTNB, Micro Method)	BioReagent	GSH-Px activity evaluation
G1527168	Glutathione Peroxidase Activity Assay Kit (NADPH Rate, UV Micro Method)	BioReagent	NADPH-coupled GPx activity detection

10.2 GSH–GSSG Cycle-Related Products

Catalog #	Product Name	Grade & Purity	Research Positioning
G774620	Glutathione (Reduced Form)	PharmPure™, Ph.Eur	GPx reducing substrate and GSH supplementation
G105427	Glutathione (Reduced Form) (GSH)	Moligand™, for cell culture, ≥98%	GSH and glutathione-cycle research
L274260	L-Glutathione (Oxidized Form)	High Purity	GSSG standard and redox-state research
G105428	L-Glutathione (Oxidized Form)	≥98%	GSH/GSSG cycle research
G1506885	Glutathione Reductase (GR)	Bioactive, ActiBioPure™, Native, High Performance, EnzymoPure™, from microorganism; ≥100 U/mg enzyme powder; ≥150 U/mg protein	GSSG reduction and GSH regeneration
G746317	Glutathione Reductase from Yeast	ActiBioPure™, Bioactive, High Performance, EnzymoPure™, Natural, >120 U/mg protein; 1000 U/mL solution	GR enzymology and glutathione-cycle research
N464348	Reduced Coenzyme II Tetrasodium Salt Hydrate (β-NADPH Tetrasodium Salt Hydrate)	≥97%(HPLC)	Electron donor for GR and GPx-coupled assays
R1492762	Reduced Glutathione (GSH) Content Assay Kit (DTNB, Micro Method)	BioReagent	Micro-scale GSH quantification
R1505409	Reduced Glutathione (GSH) Content Assay Kit (DTNB, Colorimetric Method)	BioReagent	Colorimetric GSH quantification
G1527172	Glutathione Reductase Activity Coefficient Assay Kit (DTNB, Colorimetric Method)	BioReagent	Evaluation of GR activity and GSH-regeneration capacity

10.3 CAT, PRDX, and Peroxide-Related Products

Catalog #	Product Name	Grade & Purity	Research Positioning
rp227647	Recombinant Catalase (CAT)	Bioactive, ActiBioPure™, High Performance, EnzymoPure™, Recombinant, ≥10 KU/mg enzyme powder; ≥25 KU/mg protein; expressed in E.coli	CAT enzymology and H₂O₂-scavenging research
H1508203	Catalase (CAT) Activity Assay Kit (UV Colorimetric Method)	BioReagent	CAT activity evaluation
C1505488	Catalase (CAT) Activity Assay Kit (Ammonium Molybdate, Micro Method)	BioReagent	CAT activity detection in microscale systems
H1492128	Catalase (CAT) Assay Kit (Peroxidase Method)	BioReagent	CAT activity detection
EJ1512382	Rat Catalase (CAT) ELISA Kit	BioReagent	Rat CAT quantification
Ab121313	Recombinant Peroxiredoxin 1/PAG Antibody	Recombinant, Validated, ExactAb™, High Performance, See COA	PRDX1 expression and redox research
H755825	Hydrogen Peroxide Solution	Suitable for microbiology, 3%	H₂O₂ oxidative-stress model
B106035	tert-Butyl Hydroperoxide (TBHP)	70% in H₂O	Organic peroxide oxidative-stress model
C109598	Cumene Hydroperoxide	≥80%	Organic peroxide and GPx substrate research

10.4 GPX4, Lipid Peroxidation, and Ferroptosis-Related Products

Catalog #	Product Name	Grade & Purity	Research Positioning
R302648	RSL3	Moligand™, ≥98%	GPX4 inhibition and ferroptosis induction
E424821	Erastin	10mM in DMSO	System Xc⁻-related GSH depletion and ferroptosis induction
E1496753	Erastin2	Moligand™, 10 mM in DMSO	GSH–GPX4-axis perturbation and ferroptosis research
F129882	Ferrostatin-1 (Fer-1)	Moligand™, ≥99%	Lipid-radical trapping and ferroptosis rescue
F408509	Ferrostatin-1 (Fer-1)	10mM in DMSO	Cellular ferroptosis inhibition research
L1424565	Liproxstatin-1 hydrochloride		Lipid peroxidation inhibition and ferroptosis validation
M1508267	Malondialdehyde (MDA) Content Assay Kit (TBA, Fluorescence Method)	BioReagent	Quantification of the lipid-peroxidation end product MDA
EJ1515213	4-Hydroxynonenal (4-HNE) ELISA Kit	BioReagent	Evaluation of 4-HNE and lipid peroxidation levels

GPx, CAT, and PRDX form a peroxide-scavenging network with different substrate selectivities and subcellular localizations. The GSH–GPx cycle links glutathione metabolism with antioxidant capacity, while GPX4 is responsible for membrane phospholipid peroxide clearance and ferroptosis defense. Combined evaluation of GPx/CAT activity, GSH status, GPX4, and lipid peroxidation can more accurately distinguish general oxidative stress from Ferroptosis-related lipid oxidation.

For more related articles, please see below:

[1] Analysis of peroxidase isoenzymes in medicinal plants and comparative activity experiments

[2] Simple identification experiments of plant peroxidases

[3] Experiments for the determination of peroxidase activity in plants

[4] Experiments showing peroxidase in cells

[5] Peroxidase Substrate Detection System

[6] peroxidase staining assay