GO:0004449 isocitrate dehydrogenase (NAD+) activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0004449 describes the molecular function of isocitrate dehydrogenase (NAD+) activity, which catalyzes the oxidative decarboxylation of isocitrate to 2-oxoglutarate using NAD+ as the electron acceptor.
• The human NAD-dependent isocitrate dehydrogenase is an αβ heterodimer, with the α subunit (IDH3A) and β subunit (IDH3B) forming the catalytic core, while the γ subunit (IDH3G) plays a regulatory role.
• This enzyme is a key regulator of the tricarboxylic acid (TCA) cycle and mitochondrial redox balance, linking carbon metabolism to NADH production.
• NAD+-dependent isocitrate dehydrogenases are found across evolution, from yeast (IDH2) to marine bacteria and diatoms, with distinct structural and kinetic properties.
• Altered activity of NAD+-dependent isocitrate dehydrogenase has been observed in human pathologies, including psoriasis and pelvic varicose veins, suggesting clinical relevance.
• CRISPR-based knockout, point mutation, and knock-in models are essential tools for dissecting the roles of IDH3 subunits and their disease-associated variants.
Description
Isocitrate dehydrogenase (NAD+) activity (GO:0004449) is a molecular function that catalyzes the conversion of isocitrate to 2-oxoglutarate (α-ketoglutarate) while reducing NAD+ to NADH. This reaction is a central step in the tricarboxylic acid (TCA) cycle and is critical for mitochondrial energy metabolism and redox homeostasis. Unlike the NADP+-dependent isocitrate dehydrogenases (IDH1 and IDH2), which are homodimers and often implicated in cancer through neomorphic mutations, the NAD+-dependent enzyme is a heterodimer in humans and plays a distinct role in oxidative metabolism. Researchers study this activity to understand fundamental mitochondrial physiology, metabolic disorders, and the metabolic reprogramming observed in cancer and other diseases. The enzyme has been characterized in diverse organisms, including humans, yeast, marine bacteria, and diatoms, revealing conserved and unique structural features. This article provides a comprehensive overview of the mechanism, genes, regulation, and research methods associated with GO:0004449, with a focus on how CRISPR-based models can advance our understanding of its biological and pathological roles.
isocitrate dehydrogenase (NAD+) activity At A Glance
| GO ID | GO:0004449 |
|---|---|
| GO term | isocitrate dehydrogenase (NAD+) activity |
| Ontology | molecular_function |
| Synonym | isocitrate dehydrogenase (NAD) activity; isocitrate:NAD+ oxidoreductase (decarboxylating); NAD dependent isocitrate dehydrogenase activity; NAD isocitrate dehydrogenase activity; NAD isocitric dehydrogenase activity; NAD-linked isocitrate dehydrogenase activity; NAD-specific isocitrate dehydrogenase activity; nicotinamide adenine dinucleotide isocitrate dehydrogenase activity |
| Definition | Catalysis of the reaction: isocitrate + NAD+ = 2-oxoglutarate + CO2 + NADH. |
| Major function | Oxidative decarboxylation of isocitrate in the TCA cycle, generating NADH and 2-oxoglutarate. |
| Cofactor | NAD+ (nicotinamide adenine dinucleotide) |
| Subcellular location | Mitochondrial matrix (in eukaryotes) |
| Enzyme class | Oxidoreductase (EC 1.1.1.41) |
What Is GO:0004449?
Isocitrate dehydrogenase (NAD+) activity is defined as the catalysis of the reaction: isocitrate + NAD+ = 2-oxoglutarate + CO2 + NADH. In other words, it is the enzyme activity that uses NAD+ as the electron acceptor to oxidatively decarboxylate isocitrate, producing 2-oxoglutarate, carbon dioxide, and NADH. This activity is distinct from NADP+-dependent isocitrate dehydrogenase activity, which uses NADP+ instead of NAD+.
Why Is isocitrate dehydrogenase (NAD+) activity Important in Cell Biology?
Isocitrate dehydrogenase (NAD+) activity is a cornerstone of mitochondrial energy metabolism and the TCA cycle, directly linking carbohydrate oxidation to NADH production for oxidative phosphorylation. Its unique heterodimeric structure in humans and its allosteric regulation make it a key node in metabolic control. Dysregulation of this activity has been linked to metabolic and proliferative disorders, including psoriasis and vascular pathologies. Understanding its mechanism and regulation is therefore essential for basic biology and for developing therapeutic strategies targeting metabolic pathways.
• Central to the TCA cycle, converting isocitrate to 2-oxoglutarate and generating NADH for ATP production.
• Maintains mitochondrial redox balance by producing NADH, which feeds into the electron transport chain.
• Human NAD-dependent isocitrate dehydrogenase is an αβ heterodimer, with distinct subunits encoded by IDH3A, IDH3B, and IDH3G.
• Mutations or altered expression of IDH3 subunits may contribute to metabolic diseases and cancer.
• Enzyme activity is modulated by substrate and modulator concentrations approximating mitochondrial conditions.
• Yeast IDH2 provides a model for studying NAD+-specific isocitrate dehydrogenase structure and function.
• The enzyme is a target for understanding metabolic reprogramming in psoriasis and vascular disorders.
• Comparative studies in marine bacteria and diatoms reveal evolutionary diversity in NAD+-dependent isocitrate dehydrogenases.
• CRISPR screens can identify synthetic lethal interactions and metabolic dependencies involving this activity.
• Small-molecule modulators of the enzyme could have therapeutic potential in metabolic diseases.
What Happens During isocitrate dehydrogenase (NAD+) activity?
Substrate Binding and Conformational Change
In simple terms: The enzyme grabs isocitrate and NAD+ and changes shape to hold them tightly.
The reaction begins with the binding of isocitrate and NAD+ to the active site of the enzyme. In the human αβ heterodimer, the α subunit (IDH3A) provides key catalytic residues, while the β subunit (IDH3B) contributes to substrate binding and structural integrity. Yeast NAD+-specific isocitrate dehydrogenase has two functionally distinct isocitrate binding sites, one catalytic and one regulatory, which modulate activity. Binding induces conformational changes that align substrates for catalysis.
Oxidative Decarboxylation
In simple terms: The enzyme removes a carbon from isocitrate as CO2 and transfers electrons to NAD+.
The catalytic mechanism involves the oxidation of isocitrate to oxalosuccinate, followed by decarboxylation to 2-oxoglutarate. NAD+ is reduced to NADH in the process. This step is rate-limiting and is tightly regulated by the availability of substrates and cofactors. The reaction is stereospecific and requires divalent metal ions such as Mn2+ or Mg2+ for catalysis.
Product Release and Enzyme Turnover
In simple terms: The enzyme releases the products and is ready to start again.
After the reaction, 2-oxoglutarate, CO2, and NADH are released from the active site. The enzyme returns to its original conformation to catalyze another round. The overall rate is influenced by the NAD+/NADH ratio and the concentrations of isocitrate and 2-oxoglutarate, as observed in mitochondrial-mimicking conditions. In yeast, the two isocitrate binding sites allow for allosteric regulation, ensuring efficient turnover under varying metabolic states.
Integration with the TCA Cycle
In simple terms: This reaction is a key step in the cycle that generates energy from food.
The NAD+-dependent isocitrate dehydrogenase reaction is a critical control point in the TCA cycle. The NADH produced contributes to oxidative phosphorylation, while 2-oxoglutarate is a precursor for glutamate and other amino acids. The enzyme's activity is coordinated with other TCA cycle enzymes to maintain metabolic flux. In humans, the heterodimeric structure allows for distinct regulatory properties compared to the NADP+-dependent isoforms.
Key Genes Involved in GO:0004449 isocitrate dehydrogenase (NAD+) activity
The following genes encode proteins that constitute or directly regulate isocitrate dehydrogenase (NAD+) activity, based on published literature.
| Gene | Major Role | Research Relevance |
|---|---|---|
| IDH3A | Catalytic α subunit of human NAD-dependent isocitrate dehydrogenase | Mutations linked to metabolic disorders; target for CRISPR knockout studies |
| IDH3B | β subunit, essential for heterodimer formation and substrate binding | Required for enzyme activity; knockout models show metabolic defects |
| IDH3G | γ subunit, regulatory role in the heterodimer | Modulates enzyme activity; potential target for allosteric regulation |
| IDH2 (yeast) | NAD+-specific isocitrate dehydrogenase in Saccharomyces cerevisiae | Model for studying enzyme structure and function; gene disruption studies |
| IDH1 | NADP+-dependent isocitrate dehydrogenase (cytoplasmic) | Distinct from GO:0004449; often studied in cancer metabolism |
| IDH2 (human) | NADP+-dependent isocitrate dehydrogenase (mitochondrial) | Distinct from GO:0004449; frequently mutated in cancers |
| IDH3A (bacterial) | NAD+-dependent isocitrate dehydrogenase in bacteria | Comparative studies of enzyme evolution |
| IDH3A (diatom) | NAD+-dependent isocitrate dehydrogenase in Phaeodactylum tricornutum | Biochemical and structural characterization |
| IDH3A (marine bacterium) | Type II NAD+-specific isocitrate dehydrogenase | Novel enzyme from Congregibacter litoralis |
| IDH3A (human) | Catalytic subunit | Key target for CRISPR point mutation to study catalytic residues |
| IDH3B (human) | Structural subunit | Knock-in of tagged versions for localization studies |
| IDH3G (human) | Regulatory subunit | Overexpression studies to assess regulatory effects |
| IDH2 (yeast) | Mitochondrial NAD+-specific isocitrate dehydrogenase | Gene disruption to study TCA cycle flux |
| IDH3A (psoriasis) | Enzyme activity in epidermis | Disease model for psoriasis treatment |
| IDH3A (ovarian vein) | Activity in lymphocytes | Pelvic varicose veins research |
How Is isocitrate dehydrogenase (NAD+) activity Regulated?
The activity of NAD+-dependent isocitrate dehydrogenase is regulated at multiple levels. In yeast, the enzyme has two distinct isocitrate binding sites, one catalytic and one regulatory, allowing allosteric control by isocitrate and other metabolites. In humans, the heterodimeric structure and the availability of NAD+ and substrates influence activity. The enzyme is also subject to modulation by the mitochondrial NAD+/NADH ratio, as demonstrated by studies using substrate and modulator concentrations approximating mitochondrial conditions. Additionally, post-translational modifications and expression levels of the IDH3 subunits may affect overall activity, though specific mechanisms require further investigation.
isocitrate dehydrogenase (NAD+) activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| IDH3A | Metabolic disorders, cancer | CRISPR knockout in cancer cell lines to assess proliferation and metabolism |
| IDH3B | Metabolic disorders | Point mutation knock-in to study subunit interactions |
| IDH3G | Regulatory dysfunction | Overexpression and knockout models to study allosteric regulation |
| IDH2 (yeast) | TCA cycle dysfunction | Yeast gene disruption to model metabolic defects |
| IDH3A (psoriasis) | Psoriasis | Epidermal cell models with altered enzyme activity |
Metabolic Disorders and Psoriasis
Altered NAD-dependent isocitrate dehydrogenase activity has been observed in the epidermis of psoriasis patients during treatment with dithranol, suggesting a role in epidermal metabolism and disease progression. This highlights the enzyme's potential as a biomarker or therapeutic target in inflammatory skin conditions.
Vascular Pathologies
Activity of NAD(P)-dependent dehydrogenases, including isocitrate dehydrogenase, in ovarian vein lymphocytes is altered in women with pelvic varicose veins, indicating a possible link between mitochondrial metabolism and venous disease. Further studies are needed to establish causality.
Cancer Metabolism
While mutations in NADP+-dependent IDH1/IDH2 are well-known in cancer, the role of NAD+-dependent isocitrate dehydrogenase (IDH3) in cancer is less clear. However, metabolic reprogramming in cancer cells often involves changes in TCA cycle enzymes, and IDH3 subunits may contribute to tumor metabolism. Research using CRISPR knockout models could elucidate these roles.
From isocitrate dehydrogenase (NAD+) activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| What is the catalytic role of IDH3A in the TCA cycle? | CRISPR knockout of IDH3A in human cell lines |
| How do disease-associated mutations affect enzyme activity? | Point mutation knock-in of IDH3A variants |
| Where is the enzyme localized within mitochondria? | Tagged knock-in of IDH3B with fluorescent protein |
| What is the effect of IDH3G overexpression on metabolism? | Overexpression cell models |
| Can we identify synthetic lethal partners of IDH3A? | CRISPR library screening in IDH3A-knockout cells |
| How does yeast IDH2 disruption affect mitochondrial function? | Yeast gene knockout |
How to Study the isocitrate dehydrogenase (NAD+) activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| NADH absorbance assay | Enzyme activity | Kinetic characterization of wild-type and mutant enzymes |
| X-ray crystallography | Three-dimensional structure | Determining subunit arrangement and active site |
| Metabolomics | Metabolite levels | Assessing TCA cycle flux and 2-oxoglutarate production |
| CRISPR knockout | Gene function | Studying loss-of-function phenotypes |
| CRISPR point mutation | Specific amino acid function | Dissecting catalytic residues |
| Knock-in tagging | Protein localization | Live-cell imaging of enzyme subunits |
| Overexpression | Gain-of-function effects | Assessing regulatory subunit roles |
| CRISPR library screening | Genetic interactions | Identifying synthetic lethal partners |
Enzymatic Activity Assays
Direct measurement of isocitrate dehydrogenase (NAD+) activity can be performed using spectrophotometric assays that monitor NADH production at 340 nm. These assays are essential for characterizing enzyme kinetics and the effects of mutations or inhibitors.
Structural Biology
X-ray crystallography and cryo-EM have been used to determine the structures of NAD+-dependent isocitrate dehydrogenases from humans, yeast, and bacteria, revealing the heterodimeric architecture and substrate binding sites.
Metabolic Flux Analysis
Isotope tracing and metabolomics can quantify flux through the TCA cycle and assess the contribution of NAD+-dependent isocitrate dehydrogenase to 2-oxoglutarate production and NADH generation.
CRISPR Screening
Genome-wide CRISPR knockout screens can identify genes that are essential in cells with altered IDH3 activity, revealing metabolic vulnerabilities and synthetic lethal interactions.
How CRISPR Can Be Used to Study GO:0004449 isocitrate dehydrogenase (NAD+) activity
Knockout
CRISPR knockout of IDH3A, IDH3B, or IDH3G can abolish NAD+-dependent isocitrate dehydrogenase activity, allowing researchers to study the consequences for TCA cycle flux, mitochondrial respiration, and cell growth. Such models are valuable for validating the enzyme's role in metabolic pathways and for identifying compensatory mechanisms.
Point Mutation
Introducing specific point mutations into IDH3A or IDH3B via CRISPR can mimic disease-associated variants or probe catalytic residues. These models help determine how single amino acid changes affect enzyme kinetics, substrate binding, and allosteric regulation, as informed by structural studies.
Knock-in
Knock-in of epitope tags or fluorescent proteins into the endogenous IDH3 loci enables real-time tracking of protein localization and interactions. This approach is useful for studying the assembly and dynamics of the heterodimer in living cells.
Overexpression
CRISPR activation (CRISPRa) or traditional overexpression constructs can increase the levels of IDH3 subunits, allowing researchers to investigate the effects of enzyme overabundance on mitochondrial metabolism and redox balance. Overexpression of the γ subunit (IDH3G) may reveal regulatory roles.
How EDITGENE Supports isocitrate dehydrogenase (NAD+) activity Research
Researchers studying isocitrate dehydrogenase (NAD+) activity-related genes often need to determine whether a candidate gene is causally involved in metabolic pathways or disease phenotypes. EDITGENE provides a comprehensive suite of CRISPR services to enable precise genetic modifications in cell models, from knockout to knock-in, tailored to the study of GO:0004449.
Contact EDITGENE today to design your custom CRISPR model for isocitrate dehydrogenase (NAD+) activity research.
Related Products
| Product name | Cat.No. | Species | Gene ID | |
|---|---|---|---|---|
| IDH3G Knockout HEK293 Cell Line | EDJ-KQ4961 | Human | 3421 | Details Get a Quote |
| IDH3B Knockout HEK293 Cell Line | EDJ-KQ4964 | Human | 3420 | Details Get a Quote |
| IDH3G Knockout A-549 Cell Line | EDJ-KQ27834 | Human | 3421 | Details Get a Quote |
| IDH3G Knockout HCT 116 Cell Line | EDJ-KQ27835 | Human | 3421 | Details Get a Quote |
| IDH3G Knockout HeLa Cell Line | EDJ-KQ27836 | Human | 3421 | Details Get a Quote |
| IDH3B Knockout A-549 Cell Line | EDJ-KQ27839 | Human | 3420 | Details Get a Quote |
| IDH3B Knockout HCT 116 Cell Line | EDJ-KQ27840 | Human | 3420 | Details Get a Quote |
| IDH3B Knockout HeLa Cell Line | EDJ-KQ27841 | Human | 3420 | Details Get a Quote |
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Frequently Asked Questions About isocitrate dehydrogenase (NAD+) activity
What is isocitrate dehydrogenase (NAD+) activity?
It is the enzyme activity that catalyzes the conversion of isocitrate to 2-oxoglutarate using NAD+ as a cofactor, producing NADH and CO2. This activity is encoded by GO:0004449.
What genes are involved in isocitrate dehydrogenase (NAD+) activity?
In humans, the main genes are IDH3A, IDH3B, and IDH3G, which form the heterodimeric enzyme. In yeast, IDH2 encodes the NAD+-specific enzyme.
How is isocitrate dehydrogenase (NAD+) activity regulated?
It is regulated by substrate availability, the NAD+/NADH ratio, and allosteric binding of isocitrate at a regulatory site, as shown in yeast and human studies.
What diseases are associated with isocitrate dehydrogenase (NAD+) activity?
Altered activity has been observed in psoriasis and pelvic varicose veins, and it may play a role in metabolic disorders and cancer.
What is the difference between NAD+ and NADP+ dependent isocitrate dehydrogenase?
NAD+-dependent isocitrate dehydrogenase (GO:0004449) uses NAD+ and is typically a heterodimer in humans, while NADP+-dependent enzymes (IDH1/IDH2) use NADP+ and are homodimers.
How can I study isocitrate dehydrogenase (NAD+) activity in the lab?
Common methods include enzymatic activity assays, metabolomics, structural biology, and CRISPR-based genetic models.
What CRISPR models are available for studying IDH3 genes?
EDITGENE offers knockout, point mutation, knock-in, and overexpression models for IDH3A, IDH3B, IDH3G, and related genes.
What is the structure of human NAD-dependent isocitrate dehydrogenase?
It is an αβ heterodimer, with the α subunit (IDH3A) and β subunit (IDH3B) forming the catalytic core, and the γ subunit (IDH3G) playing a regulatory role.
Can isocitrate dehydrogenase (NAD+) activity be targeted therapeutically?
It is a potential target for metabolic diseases, but further research is needed to develop specific modulators.
Where is isocitrate dehydrogenase (NAD+) activity located in the cell?
In eukaryotes, it is located in the mitochondrial matrix, where it functions in the TCA cycle.
Conclusion
Isocitrate dehydrogenase (NAD+) activity (GO:0004449) is a fundamental molecular function in mitochondrial metabolism, catalyzing a key step in the TCA cycle. Its heterodimeric structure in humans and its regulation by substrates and cofactors make it an important subject for metabolic research. Dysregulation has been linked to diseases such as psoriasis and vascular disorders, and its role in cancer metabolism is an active area of investigation. CRISPR-based models, including knockout, point mutation, knock-in, and overexpression, provide powerful tools to dissect the function of IDH3 subunits and their contributions to health and disease. EDITGENE offers comprehensive services to support these studies, from custom cell line generation to bioinformatics analysis.
References
- 1. Sun P et al.. 2019. Molecular basis for the function of the αβ heterodimer of human NAD-dependent isocitrate dehydrogenase.. J Biol Chem 294(44):16214-16227 PMID: 31515270
- 2. Gabriel JL et al.. 1986. Activity of purified NAD-specific isocitrate dehydrogenase at modulator and substrate concentrations approximating conditions in mitochondria.. Metabolism 35(7):661-7 PMID: 3724458
- 3. Huang SP et al.. 2020. Biochemical Characterization and Crystal Structure of a Novel NAD(+)-Dependent Isocitrate Dehydrogenase from Phaeodactylum tricornutum.. Int J Mol Sci 21(16) PMID: 32824636
- 4. Hammar H. 1975. Epidermal activity of NAD-dependent isocitrate dehydrogenase in psoriasis during treatment with dithranol.. J Invest Dermatol 65(3):315-9 PMID: 169306
- 5. Semendyaev AA et al.. 2024. Activity of NAD(P)-Dependent Dehydrogenases of Ovarian Vein Lymphocytes in Women with Pelvic Varicose Veins.. Bull Exp Biol Med 178(1):34-39 PMID: 39572490
- 6. Wu MC et al.. 2015. A Novel Type II NAD+-Specific Isocitrate Dehydrogenase from the Marine Bacterium Congregibacter litoralis KT71.. PLoS One 10(5):e0125229 PMID: 25942017
- 7. Lin AP et al.. 2002. Isocitrate binding at two functionally distinct sites in yeast NAD+-specific isocitrate dehydrogenase.. J Biol Chem 277(25):22475-83 PMID: 11953438
- 8. Cupp JR et al.. 1991. NAD(+)-dependent isocitrate dehydrogenase. Cloning, nucleotide sequence, and disruption of the IDH2 gene from Saccharomyces cerevisiae.. J Biol Chem 266(33):22199-205 PMID: 1939242
