GO:0016406 carnitine O-acyltransferase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0016406 carnitine O-acyltransferase activity describes the catalysis of acyl group transfer to the oxygen atom of carnitine, a central reaction in mitochondrial fatty acid oxidation.
• This activity is essential for shuttling long-chain fatty acids into mitochondria as acylcarnitines, linking lipid metabolism to energy production.
• Enzymes with this activity include carnitine palmitoyltransferases (CPT1A, CPT1B, CPT1C, CPT2) and carnitine O-acetyltransferase (CRAT), which together maintain acyl-CoA homeostasis.
• Dysregulation of carnitine O-acyltransferase activity is implicated in hepatic steatosis, steatohepatitis, and cancer metabolism.
• CRISPR-based knockout, point mutation, knock-in, and overexpression models enable precise interrogation of genes encoding carnitine O-acyltransferases.
• Studying this activity benefits from integrated methods such as RNA-seq, proteomics, metabolomics, and acylcarnitine profiling.
Description
Carnitine O-acyltransferase activity (GO:0016406) is a molecular function defined as the catalysis of acyl group transfer to an oxygen atom on the carnitine molecule. This reaction is fundamental to fatty acid metabolism because it converts acyl-CoAs into acylcarnitines, thereby facilitating the transport of fatty acids across the mitochondrial membrane for beta-oxidation. The activity is carried out by a family of enzymes including carnitine palmitoyltransferase 1 (CPT1) isoforms, carnitine palmitoyltransferase 2 (CPT2), and carnitine O-acetyltransferase (CRAT), which together regulate the flux of fatty acids into oxidative pathways. Researchers study this activity to understand energy homeostasis, lipid signaling, and the metabolic reprogramming observed in diseases such as steatohepatitis and cancer. Because carnitine O-acyltransferases sit at the crossroads of lipid synthesis and degradation, their functional characterization is critical for developing therapies targeting metabolic disorders.
carnitine O-acyltransferase activity At A Glance
| GO ID | GO:0016406 |
|---|---|
| GO term | carnitine O-acyltransferase activity |
| Ontology | molecular_function |
| Synonym | none |
| Major function | Transfer of an acyl group to the oxygen atom of carnitine, forming acylcarnitines |
| EC number | 2.3.1.- (acyltransferases acting on carnitine) |
| Representative enzymes | CPT1A, CPT1B, CPT1C, CPT2, CRAT |
| Pathway context | Mitochondrial fatty acid oxidation and acyl-CoA homeostasis |
| Disease relevance | Hepatic steatosis, steatohepatitis, cancer metabolism |
What Is GO:0016406?
In our own words, carnitine O-acyltransferase activity (GO:0016406) is the enzymatic capability to transfer an acyl group from an acyl-CoA donor to the hydroxyl oxygen of carnitine, producing acylcarnitine and free CoA. This activity is reversible and is central to the carnitine shuttle, which moves activated fatty acids into mitochondria for oxidation.
Why Is carnitine O-acyltransferase activity Important in Cell Biology?
Carnitine O-acyltransferase activity is indispensable for mitochondrial fatty acid oxidation, a process that supplies energy and maintains lipid homeostasis. Its dysregulation contributes to metabolic diseases such as hepatic steatosis and steatohepatitis, and it influences cancer cell survival by modulating lipid availability. Understanding this activity at the molecular level provides a foundation for therapeutic strategies aimed at metabolic reprogramming.
• Enables mitochondrial import of long-chain fatty acids for beta-oxidation.
• Regulates acyl-CoA/CoA ratios and cellular energy balance.
• Dysregulation is linked to non-alcoholic steatohepatitis and hepatic steatosis.
• Modulates cancer cell metabolism and autophagy, as shown for CPT2 inhibition in colorectal cancer.
• Impacts lipid droplet-associated mitochondrial metabolism in bovine liver.
• Influences dietary lipid utilization in aquaculture species.
• Provides targets for CRISPR-based functional genomics in metabolic research.
• Serves as a biomarker for fatty acid oxidation disorders and metabolic stress.
Molecular Mechanism of carnitine O-acyltransferase activity
Substrate recognition and acyl-CoA binding
In simple terms: The enzyme grabs an activated fatty acid (acyl-CoA) and a carnitine molecule.
Carnitine O-acyltransferases bind long-chain acyl-CoAs and carnitine in a sequential mechanism. The enzyme recognizes the acyl chain length and the CoA moiety, positioning the thioester bond for nucleophilic attack by the carnitine hydroxyl group. This step is critical for selecting which fatty acids enter the mitochondria.
Catalytic transfer of the acyl group
In simple terms: The fatty acid is handed over to carnitine, forming acylcarnitine.
The catalytic mechanism involves the transfer of the acyl group from acyl-CoA to the oxygen atom of carnitine, yielding acylcarnitine and free CoA. This reaction is reversible and is driven by substrate availability and product removal. The formation of acylcarnitine is the essential step for fatty acid transport across the mitochondrial membrane.
Cofactors and coenzyme A recycling
In simple terms: CoA is released and recycled for other metabolic reactions.
The reaction liberates free CoA, which can be reused in pathways such as the TCA cycle and fatty acid synthesis. The balance between acyl-CoA and free CoA is maintained by the activity of carnitine O-acyltransferases, influencing overall metabolic flux.
Regulation by malonyl-CoA and hormonal signals
In simple terms: The enzyme can be turned on or off by cellular signals.
CPT1, a key carnitine O-acyltransferase, is inhibited by malonyl-CoA, linking fatty acid oxidation to fatty acid synthesis. Hormonal signals such as insulin and glucagon modulate enzyme expression and activity, adjusting fatty acid oxidation to energy demand.
Tissue-specific isoforms and subcellular localization
In simple terms: Different versions of the enzyme work in different tissues and locations.
CPT1A (liver), CPT1B (muscle), and CPT1C (brain) are located on the outer mitochondrial membrane, while CPT2 is on the inner membrane. CRAT is peroxisomal and mitochondrial. This compartmentalization ensures efficient fatty acid trafficking and specialized metabolic roles.
Key Genes Involved in GO:0016406 carnitine O-acyltransferase activity
The following genes encode enzymes with carnitine O-acyltransferase activity or directly regulate this function.
| Gene | Major Role | Research Relevance |
|---|---|---|
| CPT1A | Liver isoform of carnitine palmitoyltransferase 1; catalyzes acyl transfer to carnitine on the outer mitochondrial membrane | Target for hepatic steatosis and metabolic studies |
| CPT1B | Muscle isoform of CPT1; regulates fatty acid oxidation in heart and skeletal muscle | Studied in energy homeostasis and cardiac metabolism |
| CPT1C | Brain-specific CPT1 isoform; involved in neuronal lipid sensing | Implicated in neurodegeneration and cancer |
| CPT2 | Inner mitochondrial membrane carnitine palmitoyltransferase; completes acyl transfer for beta-oxidation | Linked to autophagy and colorectal cancer proliferation |
| CRAT | Carnitine O-acetyltransferase; transfers acetyl groups to carnitine | Regulates acetyl-CoA homeostasis and gene expression |
| SLC25A20 | Carnitine-acylcarnitine translocase; transports acylcarnitines across inner membrane | Essential for carnitine shuttle function |
| ACADVL | Very long-chain acyl-CoA dehydrogenase; downstream of carnitine shuttle | Marker of fatty acid oxidation flux |
| PPARA | Peroxisome proliferator-activated receptor alpha; regulates CPT1A expression | Master regulator of lipid metabolism |
| TXNIP | Thioredoxin-interacting protein; modulates autophagy and fatty acid oxidation | Attenuates steatohepatitis via CPT1A regulation |
| DGAT1 | Diacylglycerol O-acyltransferase 1; involved in lipid droplet metabolism | Peridroplet mitochondrial fatty acid metabolism |
| DGAT2 | Diacylglycerol O-acyltransferase 2; synthesizes triglycerides | Linked to hepatic steatosis |
| GPAT4 | Glycerol-3-phosphate acyltransferase 4; glycerophospholipid biosynthesis | Modulates CPT2 inhibition effects in cancer |
| MALONYL-CoA | Not a gene; metabolite that inhibits CPT1 | Key regulator of fatty acid oxidation |
| INS | Insulin; hormone regulating CPT1 expression | Endocrine control of lipid metabolism |
| GCG | Glucagon; hormone stimulating fatty acid oxidation | Counter-regulatory hormone |
| LEP | Leptin; regulates energy balance and CPT1 activity | Studied in obesity models |
| SREBF1 | Sterol regulatory element-binding transcription factor 1; regulates lipogenic genes | Cross-talk with fatty acid oxidation |
How Is carnitine O-acyltransferase activity Regulated?
Carnitine O-acyltransferase activity is regulated at multiple levels. The CPT1 isoforms are inhibited by malonyl-CoA, the first committed intermediate in fatty acid synthesis, creating a reciprocal relationship between fatty acid oxidation and synthesis. Hormones such as insulin and glucagon modulate enzyme expression and activity in response to nutritional status. Additionally, the activity of CRAT is influenced by acetyl-CoA availability, affecting acetylcarnitine production and acetyl-CoA buffering. In disease states, inflammatory and metabolic signals can alter the expression of carnitine O-acyltransferases, as seen in steatohepatitis where TXNIP modulates fatty acid oxidation.
carnitine O-acyltransferase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| CPT1A | Hepatic steatosis, steatohepatitis | Liver-specific knockout mouse |
| CPT2 | Colorectal cancer, autophagy | Cancer cell line knockout |
| TXNIP | Steatohepatitis, autophagy | Txnip knockout mouse |
| DGAT1/DGAT2 | Bovine hepatic lipid metabolism | Bovine hepatocyte overexpression |
| GPAT4 | Cancer glycerophospholipid biosynthesis | GPAT4 knockout cancer cells |
Hepatic steatosis and steatohepatitis
Impaired carnitine O-acyltransferase activity contributes to lipid accumulation in the liver. Studies show that TXNIP deficiency attenuates steatohepatitis by enhancing autophagy and fatty acid oxidation, partly through regulation of CPT1A. Methionine restriction prevents the progression of hepatic steatosis in leptin-deficient obese mice, highlighting the role of fatty acid oxidation in disease progression.
Cancer metabolism
CPT2 inhibition enhances selective autophagy and proliferation in colorectal cancer via GPAT4-dependent glycerophospholipid biosynthesis, demonstrating that carnitine O-acyltransferase activity can influence tumor cell survival. This suggests that targeting this activity may be a therapeutic strategy in cancers with altered lipid metabolism.
Metabolic disorders in livestock and aquaculture
In bovine liver, diacylglycerol O-acyltransferase isoforms play a role in peridroplet mitochondrial fatty acid metabolism, indicating that carnitine O-acyltransferase activity is relevant to production animal health. In large yellow croaker, dietary lysolecithin and phosphatidylserine supplementation affect lipid metabolism and inflammation-related gene expression, including genes related to fatty acid oxidation.
From carnitine O-acyltransferase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of CPT1A reduce fatty acid oxidation? | CPT1A knockout cell line or mouse |
| Does a point mutation in CPT2 alter enzyme kinetics? | CRISPR point-mutation knock-in |
| Can CPT1B overexpression enhance muscle fatty acid oxidation? | CPT1B overexpression vector |
| Does tagging CRAT reveal its subcellular localization? | CRAT knock-in with fluorescent tag |
| Does CPT2 inhibition affect autophagy in cancer? | CPT2 knockout or inhibitor-treated cancer cells |
| Does dietary lipid modulate CPT1 expression? | Dietary intervention in fish models |
How to Study the carnitine O-acyltransferase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| RNA-seq | Gene expression levels | Transcriptional regulation of CPT1A, CPT2, CRAT |
| Proteomics | Protein abundance and modifications | Enzyme expression in disease models |
| Metabolomics | Acylcarnitine and acyl-CoA levels | Functional readout of enzyme activity |
| Enzymatic assay | Catalytic activity | Kinetic characterization of mutants |
| CRISPR screen | Gene essentiality and modifiers | Discovery of regulators |
| Western blot | Protein expression | Validation of knockout or overexpression |
| Immunofluorescence | Subcellular localization | Mitochondrial vs peroxisomal localization |
RNA-seq and transcriptomics
RNA sequencing can quantify expression of genes encoding carnitine O-acyltransferases and related metabolic genes under different conditions, such as TXNIP knockout or dietary interventions.
Proteomics and metabolomics
Mass spectrometry-based proteomics and metabolomics can measure enzyme abundance and acylcarnitine profiles, providing direct readouts of carnitine O-acyltransferase activity.
Enzymatic activity assays
Radiolabeled or fluorometric assays using acyl-CoA and carnitine substrates can quantify carnitine O-acyltransferase activity in cell lysates or mitochondrial fractions.
CRISPR screening and functional genomics
Genome-wide CRISPR knockout screens can identify genes that modulate carnitine O-acyltransferase activity or fatty acid oxidation, as demonstrated in cancer metabolism studies.
How CRISPR Can Be Used to Study GO:0016406 carnitine O-acyltransferase activity
Knockout
CRISPR knockout of CPT1A, CPT2, or CRAT can abolish carnitine O-acyltransferase activity, revealing its role in fatty acid oxidation and disease. For example, CPT2 knockout enhances autophagy in colorectal cancer cells.
Point Mutation
Introducing point mutations in catalytic residues of CPT1A or CPT2 can dissect the enzymatic mechanism and identify residues critical for acyl transfer.
Knock-in
Knock-in of tagged versions of CPT1A or CRAT allows tracking of protein localization and interactions in live cells, providing insights into the carnitine shuttle.
Overexpression
Overexpression of CPT1A or CPT1B can increase fatty acid oxidation capacity, useful for studying metabolic flux and energy homeostasis.
How EDITGENE Supports carnitine O-acyltransferase activity Research
Researchers studying carnitine O-acyltransferase activity-related genes often need to determine whether a candidate gene is causally involved in fatty acid oxidation, lipid homeostasis, or disease progression. EDITGENE provides comprehensive CRISPR-based services to generate precisely engineered cell models for such functional studies.
Contact EDITGENE today to design your custom CRISPR model for carnitine O-acyltransferase activity research.
Frequently Asked Questions About carnitine O-acyltransferase activity
What is carnitine O-acyltransferase activity?
Carnitine O-acyltransferase activity (GO:0016406) is the catalysis of acyl group transfer to the oxygen atom of carnitine, forming acylcarnitines, which is essential for mitochondrial fatty acid oxidation.
What genes are involved in carnitine O-acyltransferase activity?
Key genes include CPT1A, CPT1B, CPT1C, CPT2, and CRAT, which encode enzymes that catalyze this activity.
How is carnitine O-acyltransferase activity regulated?
It is regulated by malonyl-CoA inhibition of CPT1, hormonal signals such as insulin and glucagon, and substrate availability.
What diseases are associated with carnitine O-acyltransferase dysfunction?
Dysfunction is linked to hepatic steatosis, steatohepatitis, and cancer metabolism, among other metabolic disorders.
How can I study carnitine O-acyltransferase activity in the lab?
Common methods include enzymatic assays, RNA-seq, proteomics, metabolomics, and CRISPR-based knockout or overexpression models.
What is the role of CPT2 in cancer?
CPT2 inhibition enhances selective autophagy and proliferation in colorectal cancer via GPAT4-dependent glycerophospholipid biosynthesis.
Does TXNIP affect carnitine O-acyltransferase activity?
TXNIP attenuates steatohepatitis via autophagy and fatty acid oxidation, partly by regulating CPT1A expression.
Can CRISPR be used to study carnitine O-acyltransferase genes?
Yes, CRISPR knockout, point mutation, knock-in, and overexpression models are powerful tools to dissect gene function in this pathway.
What is the carnitine shuttle?
The carnitine shuttle is a transport system that uses carnitine O-acyltransferase activity to move fatty acids into mitochondria for beta-oxidation.
Which tissues express carnitine O-acyltransferases?
CPT1A is predominant in liver, CPT1B in muscle and heart, CPT1C in brain, and CRAT is widely expressed in mitochondria and peroxisomes.
Conclusion
Carnitine O-acyltransferase activity (GO:0016406) is a cornerstone of fatty acid metabolism, enabling mitochondrial import of fatty acids and maintaining acyl-CoA homeostasis. Its dysregulation is implicated in hepatic steatosis, steatohepatitis, and cancer, making it a compelling target for metabolic research. Advances in CRISPR-based models and multi-omics approaches continue to illuminate the mechanistic details and therapeutic potential of this activity.
References
- 1. Park HS et al.. 2021. TXNIP/VDUP1 attenuates steatohepatitis via autophagy and fatty acid oxidation.. Autophagy 17(9):2549-2564 PMID: 33190588
- 2. Wang S et al.. 2024. Diacylglycerol O-acyltransferase isoforms play a role in peridroplet mitochondrial fatty acid metabolism in bovine liver.. J Dairy Sci 107(11):9897-9914 PMID: 38851581
- 3. Weng M et al.. 2022. Effects of dietary lysolecithin on growth performance, serum biochemical indexes, antioxidant capacity, lipid metabolism and inflammation-related genes expression of juvenile large yellow croaker (Larimichthys crocea).. Fish Shellfish Immunol 128:50-59 PMID: 35843522
- 4. Malloy VL et al.. 2013. Methionine restriction prevents the progression of hepatic steatosis in leptin-deficient obese mice.. Metabolism 62(11):1651-61 PMID: 23928105
- 5. Chen M et al.. 2026. Effects of phosphatidylserine supplementation on growth performance, lipid metabolism, antioxidant capacity, and inflammatory response of juvenile large yellow croaker (Larimichthys crocea) fed with high soybean oil diets.. Comp Biochem Physiol B Biochem Mol Biol 284:111193 PMID: 41638302
- 6. Li K et al.. 2025. CPT2 inhibition enhances selective autophagy and proliferation in colorectal cancer via GPAT4-dependent glycerophospholipid biosynthesis.. Commun Biol 8(1):1480 PMID: 41107458
- 7. Zammit VA. 1981. Regulation of hepatic fatty acid metabolism. The activities of mitochondrial and microsomal acyl-CoA:sn-glycerol 3-phosphate O-acyltransferase and the concentrations of malonyl-CoA, non-esterified and esterified carnitine, glycerol 3-phosphate, ketone bodies and long-chain acyl-CoA esters in livers of fed or starved pregnant, lactating and weaned rats.. Biochem J 198(1):75-83 PMID: 7326003
- 8. Tol VA. 1975. Aspects of long-chain acyl-COA metabolism.. Mol Cell Biochem 7(1):19-31 PMID: 1134497
