GO:0004613 phosphoenolpyruvate carboxykinase (GTP) activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0004613 describes the molecular function phosphoenolpyruvate carboxykinase (GTP) activity, which catalyzes the reversible conversion of oxaloacetate and GTP to phosphoenolpyruvate, GDP, and CO2.
• This activity is essential for gluconeogenesis and glyceroneogenesis, linking tricarboxylic acid cycle intermediates to glucose production.
• The cytosolic isoform PCK1 and mitochondrial isoform PCK2 are the principal GTP-dependent enzymes in vertebrates, with distinct metabolic roles.
• PCK1 activity is regulated by self-acetylation at the active site, which controls its catalytic output.
• Loss of PCK1 in hepatic stellate cells drives liver fibrosis by fueling the TCA cycle and increasing glycolysis.
• PCK2 counteracts ferroptosis through its catalytic activity, independent of mitochondrial stress.
Description
Phosphoenolpyruvate carboxykinase (GTP) activity, encoded by the GO term GO:0004613, is a molecular function that catalyzes the GTP-dependent decarboxylation of oxaloacetate to phosphoenolpyruvate, yielding GDP and CO2. This reaction is a critical step in gluconeogenesis and glyceroneogenesis, allowing organisms to synthesize glucose from non-carbohydrate precursors such as lactate, glycerol, and amino acids. The enzyme is highly conserved across vertebrates and some bacteria, and its activity is central to metabolic homeostasis. Researchers study this activity to understand how cells maintain energy balance, adapt to nutrient stress, and contribute to diseases such as diabetes, obesity, and cancer. The GTP dependence distinguishes it from the ATP-dependent isoform found in some species, and this specificity has implications for drug design and metabolic engineering. Given its role in both normal physiology and disease, GO:0004613 is a key target for functional genomics and therapeutic development.
phosphoenolpyruvate carboxykinase (GTP) activity At A Glance
| GO ID | GO:0004613 |
|---|---|
| GO term | phosphoenolpyruvate carboxykinase (GTP) activity |
| Ontology | molecular_function |
| Synonym | GTP:oxaloacetate carboxy-lyase (transphosphorylating); phosphoenolpyruvate carboxylase (GTP); phosphopyruvate carboxylase (GTP) |
| Major function | Catalyzes the GTP-dependent conversion of oxaloacetate to phosphoenolpyruvate, a rate-limiting step in gluconeogenesis and glyceroneogenesis. |
| Reaction | GTP + oxaloacetate = GDP + phosphoenolpyruvate + CO2 |
| Cofactors | Divalent metal ions such as Mn2+ or Mg2+ are typically required for catalysis. |
| Subcellular location | Cytosolic (PCK1) and mitochondrial (PCK2) isoforms exist in vertebrates. |
| Regulation | Activity is modulated by acetylation, substrate availability, and hormonal signals. |
What Is GO:0004613?
Phosphoenolpyruvate carboxykinase (GTP) activity is defined as the catalysis of the reaction: GTP + oxaloacetate = GDP + phosphoenolpyruvate + CO2. This activity enables the transfer of a phosphate group from GTP to oxaloacetate, coupled with decarboxylation, to form phosphoenolpyruvate. It is a reversible reaction that plays a pivotal role in carbon flux between the tricarboxylic acid cycle and glycolysis/gluconeogenesis.
Why Is phosphoenolpyruvate carboxykinase (GTP) activity Important in Cell Biology?
Phosphoenolpyruvate carboxykinase (GTP) activity is a cornerstone of metabolic flexibility, enabling organisms to maintain blood glucose levels during fasting and to recycle carbon skeletons for biosynthetic pathways. Its dysregulation is linked to metabolic disorders, cancer, and fibrosis, making it a focal point for research into disease mechanisms and therapeutic interventions. Understanding this activity at the molecular level informs the development of small-molecule modulators and CRISPR-based models for studying metabolic reprogramming.
• Central to gluconeogenesis, the process by which the liver and kidneys produce glucose from non-carbohydrate sources.
• Supports glyceroneogenesis, a pathway critical for lipid homeostasis and adipocyte function.
• Plays a role in the TCA cycle anaplerosis by converting oxaloacetate to phosphoenolpyruvate.
• Its cytosolic isoform PCK1 is a key regulator of hepatic glucose output and is implicated in type 2 diabetes.
• The mitochondrial isoform PCK2 contributes to cancer cell survival and ferroptosis resistance.
• Loss of PCK1 in hepatic stellate cells promotes liver fibrosis, highlighting its role in tissue remodeling.
• Enzyme activity is regulated by post-translational modifications such as acetylation, offering a target for pharmacological intervention.
• GTP-dependent PCK enzymes are found in bacteria such as Mycobacterium smegmatis, providing evolutionary insights.
• Human liver PCK activity has been measured for forensic and clinical applications.
• CRISPR screens can identify synthetic lethal interactions with PCK1/PCK2, guiding cancer therapy.
Molecular Mechanism of phosphoenolpyruvate carboxykinase (GTP) activity
Substrate Binding and Metal Cofactor Requirement
In simple terms: The enzyme grabs oxaloacetate and GTP, using a metal helper to position them for reaction.
The catalytic cycle begins with the binding of oxaloacetate and GTP to the active site of phosphoenolpyruvate carboxykinase. Divalent metal ions, typically Mn2+ or Mg2+, are essential cofactors that stabilize the transition state and facilitate decarboxylation. Structural studies of cold-adapted PCK enzymes reveal that specific residues coordinate the metal ion and orient the substrates for efficient catalysis. The GTP molecule serves as the phosphoryl donor, distinguishing this activity from ATP-dependent isoforms.
Decarboxylation and Phosphoryl Transfer
In simple terms: The enzyme removes a carbon dioxide molecule from oxaloacetate and attaches a phosphate from GTP to form PEP.
Following substrate binding, the enzyme catalyzes the decarboxylation of oxaloacetate, releasing CO2. Concurrently, the terminal phosphate group of GTP is transferred to the enolate intermediate, forming phosphoenolpyruvate (PEP) and GDP. This concerted mechanism ensures that the energy from GTP hydrolysis is coupled to the formation of the high-energy PEP molecule. The reaction is reversible, allowing the enzyme to function in both gluconeogenesis and cataplerosis depending on metabolic demands.
Active Site Architecture and Self-Acetylation
In simple terms: The enzyme's active site can be chemically modified by acetylation, which acts like a switch to control its speed.
The active site of PCK1 contains a conserved lysine residue that can undergo self-acetylation, using acetyl-CoA as a donor. This modification inhibits enzyme activity by interfering with substrate binding and catalysis. Structural analyses have shown that acetylation induces conformational changes that reduce the affinity for oxaloacetate and GTP. This autoregulatory mechanism links the enzyme's activity to cellular acetyl-CoA levels, integrating metabolic status with gluconeogenic flux.
Isoform-Specific Catalysis and Compartmentalization
In simple terms: There are two main versions of the enzyme, one in the cytosol and one in mitochondria, each tuned for different jobs.
Vertebrates express two GTP-dependent PCK isoforms: cytosolic PCK1 and mitochondrial PCK2. PCK1 primarily supports gluconeogenesis and glyceroneogenesis in the cytosol, while PCK2 participates in mitochondrial anaplerosis and cataplerosis, influencing TCA cycle flux and redox balance. PCK2 has been shown to counteract ferroptosis through its catalytic activity, independent of mitochondrial stress responses. The distinct subcellular localizations allow for compartmentalized metabolic regulation.
Evolutionary and Structural Adaptations
In simple terms: The enzyme can adapt to different temperatures and environments, as seen in cold-adapted species.
Structural studies of cold-adapted phosphoenolpyruvate carboxykinase from Antarctic fish reveal unique amino acid substitutions that enhance catalytic efficiency at low temperatures. These adaptations include increased flexibility in loop regions and altered metal coordination, which lower the activation energy of the reaction. Such findings provide insights into enzyme evolution and have biotechnological implications for cold-active biocatalysts.
Key Genes Involved in GO:0004613 phosphoenolpyruvate carboxykinase (GTP) activity
The following genes encode proteins that exhibit or regulate phosphoenolpyruvate carboxykinase (GTP) activity, as supported by published literature.
| Gene | Major Role | Research Relevance |
|---|---|---|
| PCK1 | Cytosolic GTP-dependent phosphoenolpyruvate carboxykinase; rate-limiting in gluconeogenesis and glyceroneogenesis | Target for diabetes and liver fibrosis research; acetylation regulation |
| PCK2 | Mitochondrial GTP-dependent phosphoenolpyruvate carboxykinase; involved in TCA cycle anaplerosis and ferroptosis resistance | Cancer metabolism and ferroptosis studies |
| PCK1 (bacterial) | GTP-dependent PCK in Mycobacterium smegmatis; vertebrate-type enzyme | Evolutionary and antibacterial target research |
| PCK1 (cold-adapted) | Cold-adapted PCK from Antarctic fish; structural adaptations for low-temperature catalysis | Enzyme engineering and structural biology |
| PCK1 (human liver) | PCK activity measured in human liver for forensic applications | Clinical and forensic toxicology |
| GTP | Substrate; phosphoryl donor in the reaction | Metabolic flux studies |
| Oxaloacetate | Substrate; decarboxylated to PEP | TCA cycle and gluconeogenesis research |
| Phosphoenolpyruvate | Product; high-energy intermediate in glycolysis/gluconeogenesis | Metabolic tracing |
| GDP | Product; formed from GTP | Enzyme kinetics |
| CO2 | Product; released during decarboxylation | Isotope labeling studies |
| Mn2+ | Cofactor; stabilizes transition state | Biophysical characterization |
| Mg2+ | Alternative cofactor | Enzyme assays |
| Acetyl-CoA | Donor for self-acetylation of PCK1 | Post-translational modification studies |
| Insulin | Hormone that regulates PCK1 expression | Diabetes research |
| Glucagon | Hormone that induces PCK1 expression | Metabolic regulation |
| PPARγ | Transcription factor regulating PCK1 in adipocytes | Glyceroneogenesis and obesity research |
| CREB | Transcription factor activating PCK1 promoter | Hormonal signaling |
| FOXO1 | Transcription factor inducing PCK1 in liver | Insulin resistance |
How Is phosphoenolpyruvate carboxykinase (GTP) activity Regulated?
Phosphoenolpyruvate carboxykinase (GTP) activity is regulated at multiple levels. Transcriptionally, PCK1 is induced by glucagon and glucocorticoids and repressed by insulin, mediated by transcription factors such as CREB, FOXO1, and PPARγ. Post-translationally, self-acetylation of PCK1 at a conserved lysine residue inhibits its catalytic activity, linking enzyme function to cellular acetyl-CoA levels. Additionally, substrate availability and metal ion concentrations modulate activity in real time. In cancer cells, PCK2 expression is often upregulated to support mitochondrial metabolism and redox balance.
phosphoenolpyruvate carboxykinase (GTP) activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| PCK1 | Liver fibrosis; hepatic stellate cell activation | Pck1 conditional knockout mice; hepatic stellate cell lines |
| PCK2 | Cancer; ferroptosis resistance | PCK2 knockout cancer cell lines; xenograft models |
| PCK1 | Type 2 diabetes; gluconeogenesis | Pck1 liver-specific knockout mice; primary hepatocytes |
| PCK1 | Obesity; glyceroneogenesis | Adipocyte-specific Pck1 knockout mice |
| PCK1 (human) | Forensic toxicology | Human liver tissue samples |
Liver Fibrosis and Hepatic Stellate Cell Activation
Lack of PCK1 in hepatic stellate cells causes liver fibrosis by fueling the tricarboxylic acid cycle and increasing glycolysis. This metabolic reprogramming supports the activation of stellate cells into myofibroblasts, leading to extracellular matrix deposition and fibrosis. The study highlights PCK1 as a potential therapeutic target for fibrotic liver diseases.
Cancer Metabolism and Ferroptosis Resistance
Mitochondrial PCK2 counteracts ferroptosis via its catalytic activity, independent of mitochondrial stress. This suggests that PCK2 supports cancer cell survival by maintaining redox homeostasis and providing precursors for antioxidant defense. Targeting PCK2 may sensitize cancer cells to ferroptosis-inducing therapies.
Diabetes and Metabolic Syndrome
PCK1 is a key enzyme in gluconeogenesis, and its dysregulation contributes to hyperglycemia in type 2 diabetes. Increased PCK1 activity in the liver leads to excessive glucose production, while impaired glyceroneogenesis in adipose tissue contributes to insulin resistance. Modulating PCK1 activity is a therapeutic strategy for diabetes.
Forensic and Clinical Applications
Phosphoenolpyruvate carboxykinase activity has been measured in human liver for forensic purposes, such as estimating postmortem interval or identifying tissue-specific enzyme patterns. This underscores the enzyme's stability and utility as a biomarker.
From phosphoenolpyruvate carboxykinase (GTP) activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| What is the effect of PCK1 loss on gluconeogenesis? | Liver-specific PCK1 knockout mice |
| How does PCK2 contribute to ferroptosis resistance? | PCK2 knockout cancer cell lines treated with ferroptosis inducers |
| Does self-acetylation regulate PCK1 activity? | PCK1 point mutant (acetylation-deficient) knock-in mice |
| What is the role of PCK1 in hepatic stellate cells? | Conditional PCK1 knockout in hepatic stellate cells |
| How does cold adaptation affect PCK structure? | Recombinant expression of cold-adapted PCK mutants |
| Can PCK1 be targeted for diabetes therapy? | Overexpression of PCK1 in hepatocytes and mouse models |
How to Study the phosphoenolpyruvate carboxykinase (GTP) activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Coupled spectrophotometric assay | Enzyme activity via NADH oxidation | Kinetic characterization of PCK1/PCK2 |
| Radioisotopic assay | 14CO2 release from 14C-oxaloacetate | Tissue activity measurements |
| X-ray crystallography | Three-dimensional structure | Active site and cold adaptation studies |
| Isothermal titration calorimetry | Binding affinity for substrates | Metal and substrate interactions |
| 13C metabolic flux analysis | Flux through PCK and TCA cycle | Cancer and liver metabolism |
| CRISPR knockout screen | Gene essentiality and synthetic lethality | Identifying PCK2 dependencies |
| Western blot | Protein expression levels | PCK1/PCK2 regulation |
| Acetylation-specific antibodies | Post-translational modification status | PCK1 self-acetylation |
Enzymatic Activity Assays
Phosphoenolpyruvate carboxykinase (GTP) activity is typically measured using coupled enzyme assays that monitor the formation of phosphoenolpyruvate or the consumption of GTP. Spectrophotometric methods couple the reaction to lactate dehydrogenase or pyruvate kinase, allowing real-time quantification. Radioisotopic assays using 14C-labeled oxaloacetate provide high sensitivity for tissue samples.
Structural Biology and Biophysics
X-ray crystallography and cryo-electron microscopy have been used to determine the structures of PCK enzymes, revealing active site architecture and metal coordination. Isothermal titration calorimetry and surface plasmon resonance measure substrate binding affinities. These methods are essential for understanding cold adaptation and inhibitor design.
Metabolic Flux Analysis
Stable isotope tracing with 13C-labeled substrates combined with mass spectrometry quantifies flux through PCK in living cells or animals. This approach identifies how PCK1 or PCK2 contribute to TCA cycle anaplerosis and gluconeogenesis. It is particularly useful for studying metabolic reprogramming in cancer and fibrosis.
CRISPR Screening and Functional Genomics
Genome-wide CRISPR knockout screens can identify genes that are synthetic lethal with PCK1 or PCK2 loss, revealing metabolic vulnerabilities. Such screens have highlighted the importance of PCK2 in ferroptosis resistance and PCK1 in liver fibrosis. These methods enable unbiased discovery of pathways that interact with phosphoenolpyruvate carboxykinase (GTP) activity.
How CRISPR Can Be Used to Study GO:0004613 phosphoenolpyruvate carboxykinase (GTP) activity
Knockout
CRISPR-Cas9 knockout of PCK1 or PCK2 is used to study loss-of-function phenotypes in cell lines and animal models. For example, PCK1 knockout in hepatic stellate cells revealed its role in liver fibrosis, while PCK2 knockout sensitized cancer cells to ferroptosis. These models help establish causality between enzyme activity and disease phenotypes.
Point Mutation
Point mutations can be introduced to dissect catalytic residues or regulatory sites. For instance, mutation of the acetylated lysine in PCK1 to arginine prevents self-acetylation, allowing researchers to study the impact on enzyme activity and gluconeogenesis. Such models are valuable for understanding post-translational regulation.
Knock-in
Knock-in of tagged PCK1 or PCK2 (e.g., FLAG or GFP) enables affinity purification and live-cell imaging. This approach can reveal subcellular localization dynamics and interaction partners. Knock-in of disease-associated mutations can also model human metabolic disorders.
Overexpression
Overexpression of PCK1 or PCK2 in cell lines or transgenic mice is used to study gain-of-function effects, such as increased gluconeogenesis or ferroptosis resistance. This is particularly useful for testing therapeutic hypotheses and for producing recombinant enzyme for structural studies.
How EDITGENE Supports phosphoenolpyruvate carboxykinase (GTP) activity Research
Researchers studying phosphoenolpyruvate carboxykinase (GTP) 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-based services to accelerate this discovery, from gene knockout to precise point mutations and library screening.
Contact EDITGENE today to design your custom CRISPR model for phosphoenolpyruvate carboxykinase (GTP) activity research.
Frequently Asked Questions About phosphoenolpyruvate carboxykinase (GTP) activity
What is phosphoenolpyruvate carboxykinase (GTP) activity?
It is the molecular function defined by GO:0004613, catalyzing the GTP-dependent conversion of oxaloacetate to phosphoenolpyruvate, GDP, and CO2.
What genes are involved in phosphoenolpyruvate carboxykinase (GTP) activity?
The main genes are PCK1 (cytosolic) and PCK2 (mitochondrial) in vertebrates, as well as bacterial homologs like that in Mycobacterium smegmatis.
What is the role of PCK1 in liver fibrosis?
Lack of PCK1 in hepatic stellate cells causes liver fibrosis by fueling the TCA cycle and increasing glycolysis.
How is phosphoenolpyruvate carboxykinase (GTP) activity regulated?
It is regulated transcriptionally by hormones like insulin and glucagon, and post-translationally by self-acetylation of PCK1.
What diseases are associated with PCK1 and PCK2?
PCK1 is linked to type 2 diabetes and liver fibrosis, while PCK2 is implicated in cancer metabolism and ferroptosis resistance.
What is the difference between PCK1 and PCK2?
PCK1 is cytosolic and primarily involved in gluconeogenesis and glyceroneogenesis, while PCK2 is mitochondrial and participates in TCA cycle anaplerosis and redox balance.
How can I measure phosphoenolpyruvate carboxykinase (GTP) activity?
It can be measured using coupled spectrophotometric assays, radioisotopic methods, or metabolic flux analysis.
What model systems are used to study PCK1 and PCK2?
Common models include liver-specific knockout mice, cancer cell lines, and CRISPR-engineered cell models.
Is phosphoenolpyruvate carboxykinase (GTP) activity a drug target?
Yes, it is considered a target for diabetes, liver fibrosis, and cancer therapies due to its central metabolic role.
What CRISPR services does EDITGENE offer for PCK research?
EDITGENE provides knockout, point mutation, knock-in, overexpression, and CRISPR library screening services for PCK1, PCK2, and related genes.
Conclusion
Phosphoenolpyruvate carboxykinase (GTP) activity (GO:0004613) is a fundamental metabolic function that bridges the TCA cycle and gluconeogenesis. Its dysregulation contributes to diabetes, liver fibrosis, and cancer, making it a compelling target for therapeutic intervention. Advances in structural biology and CRISPR-based models continue to unravel its regulatory mechanisms and disease relevance. EDITGENE's comprehensive CRISPR services empower researchers to dissect the roles of PCK1 and PCK2 in health and disease, accelerating the development of novel treatments.
References
- 1. McLeod MJ et al.. 2025. Structural mechanisms for cold-adapted activity of phosphoenolpyruvate carboxykinase.. Protein Sci 34(11):e70326 PMID: 41099612
- 3. Hanson RW et al.. 2003. Glyceroneogenesis revisited.. Biochimie 85(12):1199-205 PMID: 14739071
- 4. Novoa E et al.. 2026. Lack of PCK1 in hepatic stellate cells causes liver fibrosis by fueling tricarboxylic acid cycle and increasing glycolysis.. Cell Metab 38(4):729-745.e9 PMID: 41734768
- 5. Cui H et al.. 2025. Mitochondrial phosphoenolpyruvate carboxykinase 2 counteracts ferroptosis via catalytic activity independent of mitochondrial stress.. Biochem Biophys Res Commun 778:152383 PMID: 40712389
- 6. Latorre-Muro P et al.. 2021. Self-acetylation at the active site of phosphoenolpyruvate carboxykinase (PCK1) controls enzyme activity.. J Biol Chem 296:100205 PMID: 33334880
- 7. Mukhopadhyay B et al.. 2001. A GTP-dependent vertebrate-type phosphoenolpyruvate carboxykinase from Mycobacterium smegmatis.. J Biol Chem 276(19):16137-45 PMID: 11278451
- 8. McGraw CA et al.. 1986. Phosphoenolpyruvate carboxykinase activity in human liver.. Forensic Sci Int 30(2-3):143-54 PMID: 3957187
