GO:0003994 aconitate hydratase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0003994 (aconitate hydratase activity) catalyzes the reversible interconversion of citrate and isocitrate via the enzyme-bound intermediate cis-aconitate, a central step of the TCA cycle.
• The reaction proceeds in two dehydration/rehydration steps: citrate to cis-aconitate plus water, then cis-aconitate plus water to isocitrate.
• Mammalian aconitase exists as cytosolic (IRP1) and mitochondrial (ACO2) forms; the cytosolic enzyme can switch between aconitase activity and RNA-binding depending on its iron-sulfur cluster.
• The iron-sulfur cluster is essential for catalysis and is a primary target of oxidative stress, linking aconitate hydratase activity to redox biology and disease.
• Aconitate hydratase activity is regulated by iron availability, bicarbonate, and the integrity of its [4Fe-4S] cluster.
• Loss of aconitase 2 function disrupts the canonical TCA cycle and citrate clearance, with implications for metabolic disorders and cancer.
Description
Aconitate hydratase activity (GO:0003994) is a molecular function that catalyzes the reversible isomerization of citrate to isocitrate through the labile intermediate cis-aconitate. This reaction is a canonical step of the tricarboxylic acid (TCA) cycle and is essential for oxidative metabolism in mitochondria, where it supports energy production and biosynthetic precursor supply. In mammals, the enzyme exists as two distinct proteins: the mitochondrial aconitase (ACO2) and the cytosolic aconitase (ACO1/IRP1), which also functions as an iron-responsive element-binding protein. The dual role of the cytosolic enzyme exemplifies how a single polypeptide can integrate metabolic and regulatory signals. Beyond its housekeeping metabolic role, aconitate hydratase activity is highly sensitive to oxidative stress because its catalytic [4Fe-4S] cluster is prone to disassembly by reactive oxygen species. This sensitivity positions the enzyme as a redox sensor and a contributor to pathologies ranging from toxic hepatitis to neurodegeneration. In plants, the iron-responsive element/iron-regulatory protein 1 (IRE/IRP1) switch does not operate, indicating evolutionary divergence in the regulation of aconitase-like proteins. In fungi such as Aspergillus niger, iron availability directly influences aconitate hydratase activity and citric acid production, underscoring the enzyme's biotechnological relevance. For researchers, GO:0003994 represents a convergence point for metabolism, iron homeostasis, and redox signaling. Understanding its mechanism, regulation, and disease connections requires integrated approaches from enzymology to CRISPR-based cell modeling.
aconitate hydratase activity At A Glance
| GO ID | GO:0003994 |
|---|---|
| GO term | aconitate hydratase activity |
| Ontology | molecular_function |
| Synonym | aconitase activity; cis-aconitase activity; citrate hydro-lyase activity; citrate(isocitrate) hydro-lyase activity; citrate(isocitrate) hydro-lyase (cis-aconitate-forming) |
| Major function | Catalyzes the reversible isomerization of citrate to isocitrate via cis-aconitate, a key step in the TCA cycle. |
| Cofactor | Requires an iron-sulfur cluster ([4Fe-4S]) for catalytic activity. |
| Subcellular location | Mitochondrial (ACO2) and cytosolic (ACO1/IRP1) isoforms in mammals. |
| Regulation | Regulated by iron availability, oxidative stress, and bicarbonate. |
| Disease relevance | Implicated in metabolic disorders, cancer, and toxic hepatitis. |
What Is GO:0003994?
According to the Gene Ontology, aconitate hydratase activity (GO:0003994) is defined as the catalysis of the reaction: citrate = isocitrate. The reaction occurs in two steps: (1) citrate = cis-aconitate + H2O, and (2) cis-aconitate + H2O = isocitrate. This reaction is the interconversion of citrate and isocitrate via the labile, enzyme-bound intermediate cis-aconitate. Water is removed from one part of the citrate molecule and added back to a different atom to form isocitrate. In essence, the enzyme dehydrates citrate to cis-aconitate and then rehydrates it to isocitrate, effectively isomerizing the substrate.
Why Is aconitate hydratase activity Important in Cell Biology?
Aconitate hydratase activity is a linchpin of cellular metabolism because it controls the flux between citrate and isocitrate in the TCA cycle, influencing energy production and biosynthetic pathways. Its cytosolic isoform, IRP1, additionally regulates iron homeostasis by binding to iron-responsive elements in mRNAs, thereby coordinating iron uptake and storage with metabolic status. The enzyme's iron-sulfur cluster makes it a sensitive redox sensor; oxidative damage to the cluster impairs activity and has been linked to liver injury and neurodegeneration. In biotechnology, aconitate hydratase activity affects citric acid production in Aspergillus niger, a major industrial fermentation product. Thus, understanding GO:0003994 is essential for metabolic engineering, disease modeling, and the development of therapies targeting metabolic reprogramming.
• Central to the TCA cycle, affecting ATP production and biosynthetic precursor supply.
• Cytosolic aconitase (IRP1) regulates iron homeostasis via the IRE/IRP system.
• Sensitive to oxidative stress due to its [4Fe-4S] cluster, linking metabolism to redox signaling.
• Dysregulation is associated with toxic hepatitis and liver injury.
• Implicated in cancer metabolism, where citrate/isocitrate flux supports growth.
• In plants, the IRE/IRP1 switch is absent, highlighting evolutionary differences in regulation.
• Bicarbonate modulates enzyme activity, connecting pH homeostasis to TCA cycle flux.
• Iron availability regulates aconitate hydratase activity in fungi, impacting citric acid production.
• Nuclear reductive carboxylation involving aconitase-related enzymes fuels histone acetylation and gene activation.
• Aconitase 2 is critical for citrate clearance, and its loss causes metabolic remodeling.
Molecular Mechanism of aconitate hydratase activity
Substrate Binding and Dehydration
In simple terms: The enzyme grabs citrate and removes a water molecule to create a reactive intermediate.
Aconitate hydratase binds citrate in its active site, where the [4Fe-4S] cluster polarizes the substrate. The enzyme catalyzes the dehydration of citrate to form cis-aconitate, releasing a water molecule. This step is reversible and requires the iron-sulfur cluster to be in its reduced state for optimal activity. The reaction is highly stereospecific, ensuring that only the correct isomer is formed.
Formation of cis-Aconitate Intermediate
In simple terms: A temporary molecule called cis-aconitate is made and held tightly by the enzyme.
The cis-aconitate intermediate remains bound to the enzyme through coordination with the iron-sulfur cluster. This labile intermediate is not released into solution but is channeled directly to the next step. The enzyme's active site architecture prevents side reactions and ensures efficient isomerization. The stability of the enzyme-bound cis-aconitate is critical for the overall catalytic cycle.
Rehydration to Isocitrate
In simple terms: Water is added back to the intermediate to produce isocitrate.
In the second step, water is added to cis-aconitate in a regio- and stereospecific manner to yield isocitrate. This rehydration completes the isomerization and releases isocitrate, which can then proceed through the TCA cycle. The reaction is reversible, allowing the enzyme to interconvert citrate and isocitrate depending on metabolic demands. The catalytic cycle requires the iron-sulfur cluster to cycle between different oxidation states.
Role of the Iron-Sulfur Cluster
In simple terms: An iron-sulfur cluster acts as the enzyme's catalytic heart.
The [4Fe-4S] cluster is essential for aconitate hydratase activity. It is coordinated by three cysteine residues and a labile iron atom that interacts with the substrate. Oxidative stress can disassemble the cluster, leading to loss of enzymatic activity and, in the cytosolic isoform, conversion to an RNA-binding protein. The cluster's sensitivity to reactive oxygen species makes the enzyme a redox sensor.
Regulation by Iron and Bicarbonate
In simple terms: Iron levels and bicarbonate can turn the enzyme's activity up or down.
Iron availability directly affects the assembly and stability of the iron-sulfur cluster, thereby regulating aconitate hydratase activity. In rat kidney cortex, bicarbonate has been shown to regulate aconitate hydratase activity, linking pH and bicarbonate homeostasis to TCA cycle flux. In mammals, oxidative stress modulates enzyme activity, and free radical oxidation can impair catalysis. These regulatory inputs allow the enzyme to adapt to changing metabolic and environmental conditions.
Key Genes Involved in GO:0003994 aconitate hydratase activity
The following genes encode proteins that exhibit aconitate hydratase activity or directly regulate it, based on published literature.
| Gene | Major Role | Research Relevance |
|---|---|---|
| ACO2 | Mitochondrial aconitase; catalyzes citrate to isocitrate in the TCA cycle | Metabolic disorders, cancer, citrate clearance |
| ACO1 | Cytosolic aconitase/IRP1; dual role in TCA cycle and iron regulation | Iron homeostasis, oxidative stress, RNA-binding |
| IRP1 | Iron-regulatory protein 1; binds IREs when aconitase activity is lost | Iron metabolism, translational regulation |
| IRP2 | Iron-regulatory protein 2; regulates iron homeostasis independent of aconitase activity | Iron metabolism, neurodegeneration |
| ISCU | Scaffold for iron-sulfur cluster assembly, required for aconitase activity | Mitochondrial function, iron-sulfur cluster disorders |
| NFS1 | Cysteine desulfurase; provides sulfur for iron-sulfur clusters | Iron-sulfur cluster biogenesis |
| FXN | Frataxin; involved in iron-sulfur cluster assembly, affects aconitase | Friedreich ataxia, mitochondrial dysfunction |
| SDHB | Succinate dehydrogenase; TCA cycle enzyme, indirect link to aconitase flux | Cancer metabolism, TCA cycle |
| IDH1 | Isocitrate dehydrogenase 1; consumes isocitrate produced by aconitase | Cancer metabolism, NADPH production |
| IDH2 | Isocitrate dehydrogenase 2; mitochondrial counterpart | Cancer, TCA cycle |
| CS | Citrate synthase; produces citrate for aconitase | TCA cycle flux, metabolic engineering |
| MDH2 | Malate dehydrogenase; TCA cycle enzyme, indirect | Metabolic disorders |
| OGDH | Alpha-ketoglutarate dehydrogenase; downstream of isocitrate | TCA cycle, cancer |
| GOT1 | Glutamate-oxaloacetate transaminase; links TCA cycle to amino acid metabolism | Reductive carboxylation, cancer |
| GOT2 | Mitochondrial transaminase; supports TCA cycle anaplerosis | Metabolic reprogramming |
| ACLY | ATP-citrate lyase; consumes citrate, competing with aconitase | Lipogenesis, cancer |
| SLC25A1 | Mitochondrial citrate carrier; transports citrate for cytosolic aconitase | Citrate metabolism, cancer |
| HIF1A | Hypoxia-inducible factor 1-alpha; regulates metabolic enzymes including aconitase | Hypoxia, cancer metabolism |
How Is aconitate hydratase activity Regulated?
Aconitate hydratase activity is regulated at multiple levels. Iron availability controls the assembly of the [4Fe-4S] cluster, and iron deficiency leads to loss of activity and, for the cytosolic enzyme, conversion to an RNA-binding protein. Oxidative stress can disassemble the cluster, reducing catalytic activity and contributing to disease pathology. Bicarbonate has been shown to regulate aconitate hydratase activity in rat kidney cortex, suggesting pH-dependent modulation. In plants, the IRE/IRP1 regulatory switch does not operate, indicating that iron-dependent regulation of aconitase is not universal. Additionally, metabolic flux through the TCA cycle can influence aconitase activity indirectly through substrate availability and feedback inhibition.
aconitate hydratase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| ACO2 | Metabolic disorders, cancer, citrate clearance | ACO2 knockout cell lines, metabolic flux analysis |
| ACO1/IRP1 | Iron homeostasis, neurodegeneration | IRP1 point mutations, IRE reporter assays |
| FXN | Friedreich ataxia, iron-sulfur cluster deficiency | FXN knockout models, aconitase activity assays |
| IDH1/2 | Cancer metabolism, TCA cycle reprogramming | IDH mutant knock-in cells, metabolomics |
| GOT1 | Reductive carboxylation, cancer | GOT1 knockout, histone acetylation studies |
Aconitate Hydratase and Liver Injury
Oxidative stress during toxic hepatitis impairs aconitate hydratase activity in rat liver, as shown by increased free radical oxidation and decreased catalytic activity. This suggests that the enzyme is a sensitive marker of hepatic oxidative damage and may contribute to disease progression. Mammalian aconitate hydratase is also affected by oxidative stress in other tissues, linking its dysfunction to broader pathology.
Cancer Metabolism and Aconitase 2
Aconitase 2 (ACO2) is critical for citrate clearance in the canonical TCA cycle, and its loss leads to metabolic remodeling that can support cancer cell growth. Nuclear-specific reductive carboxylation of alpha-ketoglutarate, which involves aconitase-related enzymes, fuels histone acetylation and gene activation, linking metabolism to epigenetic regulation in cancer. These findings highlight aconitate hydratase activity as a potential target in cancer metabolism.
Iron Homeostasis and Neurodegeneration
The cytosolic aconitase IRP1 regulates iron homeostasis, and its dysfunction has been implicated in neurodegenerative disorders. In plants, the IRE/IRP1 switch does not operate, but in mammals, the dual role of IRP1 connects iron metabolism to neurodegeneration. Oxidative stress can disrupt the iron-sulfur cluster, leading to altered iron regulation and potential neuronal damage.
From aconitate hydratase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of ACO2 affect TCA cycle flux and citrate clearance? | ACO2 knockout cell lines |
| How does the iron-sulfur cluster regulate aconitase activity? | Point mutations in cluster-coordinating cysteines |
| Can restoration of aconitase activity rescue oxidative stress phenotypes? | Knock-in of wild-type ACO2 in mutant cells |
| What is the role of cytosolic aconitase in iron regulation? | Tagged IRP1 knock-in for RNA-binding assays |
| Does overexpression of aconitase alter citric acid production? | Overexpression in Aspergillus niger |
| How does bicarbonate regulate aconitate hydratase? | Bicarbonate-treated kidney cortex cells |
How to Study the aconitate hydratase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Spectrophotometric assay | Aconitase enzymatic activity | Quantifying activity in cell lysates |
| 13C metabolic flux analysis | Flux through citrate/isocitrate | Metabolic reprogramming studies |
| EPR spectroscopy | Iron-sulfur cluster integrity | Oxidative stress effects |
| CRISPR knockout screens | Genes affecting aconitase activity | Cancer metabolism targets |
| RNA-seq | Transcriptional changes upon ACO2 loss | Metabolic gene expression |
| Proteomics | Protein interactions and modifications | IRP1 RNA-binding partners |
| Histone acetylation assays | Epigenetic changes from reductive carboxylation | Nuclear aconitase-related metabolism |
| Citric acid production assay | Fungal fermentation output | Aspergillus niger engineering |
Enzymatic Activity Assays
Aconitate hydratase activity can be measured spectrophotometrically by monitoring the formation of cis-aconitate at 240 nm or by coupled assays with isocitrate dehydrogenase. These assays are used to quantify enzyme activity in cell lysates and purified preparations.
Metabolic Flux Analysis
Stable isotope tracing with 13C-labeled substrates combined with mass spectrometry allows researchers to measure flux through the aconitase step in the TCA cycle. This method is essential for understanding how genetic perturbations affect citrate/isocitrate interconversion.
Iron-Sulfur Cluster Analysis
The integrity of the [4Fe-4S] cluster can be assessed by electron paramagnetic resonance (EPR) spectroscopy or by measuring iron content. These techniques are used to study how oxidative stress or mutations affect cluster stability and enzyme activity.
CRISPR-Based Genetic Screens
Genome-wide CRISPR knockout screens can identify genes that regulate aconitate hydratase activity or that are synthetically lethal with ACO2 loss. Such screens are powerful for uncovering metabolic vulnerabilities in cancer cells.
How CRISPR Can Be Used to Study GO:0003994 aconitate hydratase activity
Knockout
CRISPR knockout of ACO2 or ACO1 can abolish aconitate hydratase activity, leading to metabolic rewiring and impaired TCA cycle flux. These models are used to study the consequences of enzyme loss in cancer and metabolic disorders.
Point Mutation
Point mutations in the iron-sulfur cluster-coordinating cysteines of ACO2 or ACO1 can disrupt catalytic activity without affecting protein stability, allowing precise structure-function studies. Such mutations are valuable for dissecting the role of the cluster in catalysis and regulation.
Knock-in
Knock-in of tagged ACO2 or ACO1 (e.g., FLAG or GFP) enables localization and interaction studies, as well as rescue experiments in knockout backgrounds. Tagged knock-ins are also useful for monitoring enzyme dynamics in live cells.
Overexpression
Overexpression of ACO2 or ACO1 can increase aconitate hydratase activity, potentially altering TCA cycle flux and citrate levels. In Aspergillus niger, overexpression of aconitase can enhance citric acid production.
How EDITGENE Supports aconitate hydratase activity Research
Researchers studying aconitate hydratase activity-related genes often need to determine whether a candidate gene is causally involved in metabolic regulation, iron homeostasis, or disease. EDITGENE provides a comprehensive suite of CRISPR-based services to generate precisely engineered cell models for such investigations.
Contact EDITGENE today to design your custom CRISPR model for aconitate hydratase activity research.
Related Products
| Product name | Cat.No. | Species | Gene ID | |
|---|---|---|---|---|
| ACO1 Knockout HEK293 Cell Line | EDJ-KQ3552 | Human | 48 | Details Get a Quote |
| IREB2 Knockout HEK293 Cell Line | EDJ-KQ5005 | Human | 3658 | Details Get a Quote |
| ACO1 Knockout A-549 Cell Line | EDJ-KQ25408 | Human | 48 | Details Get a Quote |
| ACO1 Knockout HCT 116 Cell Line | EDJ-KQ25409 | Human | 48 | Details Get a Quote |
| ACO1 Knockout HeLa Cell Line | EDJ-KQ25410 | Human | 48 | Details Get a Quote |
| IREB2 Knockout A-549 Cell Line | EDJ-KQ27908 | Human | 3658 | Details Get a Quote |
| IREB2 Knockout HCT 116 Cell Line | EDJ-KQ27909 | Human | 3658 | Details Get a Quote |
| IREB2 Knockout HeLa Cell Line | EDJ-KQ27910 | Human | 3658 | Details Get a Quote |
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Frequently Asked Questions About aconitate hydratase activity
What is aconitate hydratase activity?
Aconitate hydratase activity (GO:0003994) is the catalysis of the reversible isomerization of citrate to isocitrate via cis-aconitate, a key step in the TCA cycle.
What genes are involved in aconitate hydratase activity?
The main genes are ACO2 (mitochondrial aconitase) and ACO1 (cytosolic aconitase/IRP1), along with iron-sulfur cluster assembly genes like ISCU and NFS1.
What is the role of aconitate hydratase in the TCA cycle?
It converts citrate to isocitrate, allowing the TCA cycle to continue and produce energy and biosynthetic precursors.
How is aconitate hydratase activity regulated?
It is regulated by iron availability, oxidative stress, and bicarbonate, which affect the iron-sulfur cluster and enzyme activity.
What diseases are associated with aconitate hydratase dysfunction?
Dysfunction has been linked to toxic hepatitis, cancer metabolism, and neurodegenerative disorders.
What is the difference between ACO1 and ACO2?
ACO1 is cytosolic and also functions as IRP1 in iron regulation, while ACO2 is mitochondrial and primarily involved in the TCA cycle.
How can I measure aconitate hydratase activity?
It can be measured spectrophotometrically by monitoring cis-aconitate formation or through coupled enzymatic assays.
Can CRISPR be used to study aconitate hydratase?
Yes, CRISPR knockout, point mutation, knock-in, and overexpression models are widely used to study its function and regulation.
What is the iron-sulfur cluster role in aconitate hydratase?
The [4Fe-4S] cluster is essential for catalysis and acts as a redox sensor; its disruption leads to loss of activity.
Is aconitate hydratase activity important in cancer?
Yes, it influences TCA cycle flux and citrate metabolism, and its dysregulation can support cancer cell growth.
Conclusion
Aconitate hydratase activity (GO:0003994) is a fundamental molecular function that bridges energy metabolism, iron homeostasis, and redox signaling. Its dual role in the TCA cycle and, for the cytosolic isoform, in iron regulation makes it a critical node in cellular physiology. Dysregulation of this activity is implicated in liver injury, cancer, and neurodegeneration, highlighting its clinical relevance. Advances in CRISPR-based models and metabolic flux analysis continue to unravel the complexities of aconitate hydratase regulation and its potential as a therapeutic target. For researchers aiming to dissect the mechanistic details of GO:0003994, precise genetic models are indispensable. EDITGENE's comprehensive CRISPR services provide the tools needed to explore the function of ACO2, ACO1, and related genes in health and disease.
References
- 1. Matasova LV et al.. 2008. Aconitate hydratase of mammals under oxidative stress.. Biochemistry (Mosc) 73(9):957-64 PMID: 18976211
- 2. Arnaud N et al.. 2007. The iron-responsive element (IRE)/iron-regulatory protein 1 (IRP1)-cytosolic aconitase iron-regulatory switch does not operate in plants.. Biochem J 405(3):523-31 PMID: 17437406
- 3. Stepiński J et al.. 1976. Regulation of aconitate hydratase activity from rat kidney cortex by bicarbonate.. Acta Biochim Pol 23(2-3):203-15 PMID: 9759
- 4. Xie A et al.. 2026. Citrate clearance is a major function of aconitase 2 in the canonical TCA cycle.. Cell 189(9):2684-2699.e21 PMID: 41763199
- 5. Haile DJ et al.. 1992. Reciprocal control of RNA-binding and aconitase activity in the regulation of the iron-responsive element binding protein: role of the iron-sulfur cluster.. Proc Natl Acad Sci U S A 89(16):7536-40 PMID: 1502165
- 6. Andreeshcheva EM et al.. 2004. Free radical oxidation and catalytic activity of aconitate hydratase in rat liver under normal conditions and during toxic hepatitis.. Bull Exp Biol Med 137(4):352-4 PMID: 15452599
- 7. Sawant Dessai A et al.. 2026. Nuclear-specific reductive carboxylation of alpha-ketoglutarate fuels histone acetylation to induce chromatin accessibility and gene activation.. Nat Commun 17(1) PMID: 42386731
- 8. Szczodrak J et al.. 1985. Effect of iron on the activity of aconitate hydratase and synthesis of citric acid by Aspergillus niger.. Zentralbl Mikrobiol 140(7):567-74 PMID: 4090766
