GO:0004013 adenosylhomocysteinase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0004013 adenosylhomocysteinase activity catalyzes the reversible hydrolysis of S-adenosyl-L-homocysteine (SAH) to adenosine and L-homocysteine, a key step in the methionine cycle.
• The enzyme, often called AHCY or SAHase, is essential for maintaining the cellular methylation potential by removing SAH, a potent inhibitor of methyltransferases.
• AHCY is involved in diverse biological processes including embryonic stem cell pluripotency, redox sensing, and tumorigenesis [6,8,3].
• Dysregulation of AHCY is linked to cancers such as non-small cell lung cancer and microsatellite instability colorectal cancer, as well as retinal degeneration [2,4,8].
• AHCY is a target for small molecules like baicalein and carbocyclic nucleosides, offering therapeutic avenues [4,7].
• CRISPR-based models (knockout, point mutation, knock-in, overexpression) are powerful tools to dissect AHCY function in health and disease.
Description
Adenosylhomocysteinase activity (GO:0004013) is a fundamental enzymatic function that catalyzes the hydrolysis of S-adenosyl-L-homocysteine (SAH) into adenosine and L-homocysteine. This reaction is a critical node in the methionine cycle and one-carbon metabolism, influencing the availability of methyl groups for essential cellular processes such as DNA, RNA, and histone methylation. Because SAH is a product inhibitor of S-adenosylmethionine (SAM)-dependent methyltransferases, the activity of adenosylhomocysteinase directly modulates the methylation potential of the cell. Researchers study this activity to understand how cells regulate gene expression, maintain pluripotency, and respond to stress [6,8]. Recent studies have revealed that adenosylhomocysteinase is not merely a housekeeping enzyme but a key player in cancer metabolism, inflammation, and redox signaling [1,2,3,4]. For example, the AHCY-adenosine complex rewires mRNA methylation to enhance fatty acid biosynthesis in tumors, and in Drosophila, Ahcy acts as a redox sensor protecting against light-induced retinal degeneration. These findings underscore the importance of GO:0004013 in both basic biology and disease pathogenesis.
adenosylhomocysteinase activity At A Glance
| GO ID | GO:0004013 |
|---|---|
| GO term | adenosylhomocysteinase activity |
| Ontology | molecular_function |
| Synonym | adenosylhomocysteine hydrolase activity; AdoHcyase activity; S-adenosylhomocysteinase activity; S-adenosylhomocysteine hydrolase activity; S-adenosylhomocysteine synthase activity; S-adenosyl-L-homocysteine hydrolase activity; SAHase activity |
| Major function | Catalyzes the hydrolysis of S-adenosyl-L-homocysteine to adenosine and L-homocysteine |
| Reaction | S-adenosyl-L-homocysteine + H2O = adenosine + L-homocysteine |
| Cofactor | NAD+ (as a cofactor in the catalytic mechanism) |
| Subcellular location | Cytoplasm, nucleus, and mitochondria |
| Pathway | Methionine cycle, one-carbon metabolism |
What Is GO:0004013?
According to the Gene Ontology, adenosylhomocysteinase activity (GO:0004013) is defined as the catalysis of the reaction: S-adenosyl-L-homocysteine + H2O = adenosine + L-homocysteine. This enzymatic activity is also known by synonyms such as AdoHcyase activity, S-adenosylhomocysteine hydrolase activity, and SAHase activity. It is a molecular function that enables the breakdown of SAH, thereby regulating the cellular concentration of this metabolite and indirectly controlling methylation reactions.
Why Is adenosylhomocysteinase activity Important in Cell Biology?
Adenosylhomocysteinase activity is crucial because it controls the intracellular levels of S-adenosylhomocysteine (SAH), a potent inhibitor of SAM-dependent methyltransferases. By hydrolyzing SAH, the enzyme maintains the methylation potential (SAM/SAH ratio) required for epigenetic regulation, including DNA and histone methylation. This activity impacts gene expression, cell differentiation, and metabolic reprogramming. Dysregulation of AHCY has been implicated in various diseases, including cancer, where it supports tumorigenesis by rewiring mRNA methylation and fatty acid biosynthesis, and in inflammation through homocysteine metabolism. Moreover, AHCY is essential for embryonic stem cell identity and pluripotency, and its redox-sensing role in Drosophila highlights its protective function against oxidative stress. Thus, understanding GO:0004013 is fundamental for both developmental biology and disease research.
• Regulates cellular methylation potential by removing SAH, a methyltransferase inhibitor.
• Supports cancer progression by enhancing fatty acid biosynthesis and mRNA methylation in tumors.
• Involved in inflammation through homocysteine metabolism and N-homocysteinylation.
• Modulates ferroptosis in non-small cell lung cancer via hydrogen sulfide-mediated persulfidation.
• Targeted by baicalein to suppress cancer stemness in microsatellite instability colorectal cancer.
• Essential for maintaining embryonic stem cell identity and pluripotency.
• Acts as a redox sensor in Drosophila, protecting against light-induced retinal degeneration.
• Inhibited by carbocyclic nucleosides, providing a basis for antiviral and anticancer drug design.
• Plays a role in homocysteine metabolism, linking to cardiovascular and neurological disorders.
• Serves as a potential therapeutic target for metabolic and epigenetic diseases.
Molecular Mechanism of adenosylhomocysteinase activity
Substrate Binding and Catalysis
In simple terms: The enzyme grabs SAH and breaks it into two harmless molecules.
Adenosylhomocysteinase binds S-adenosyl-L-homocysteine (SAH) in its active site, where a NAD+ cofactor is essential for catalysis. The enzyme catalyzes the reversible hydrolysis of SAH to adenosine and L-homocysteine. This reaction proceeds through an oxidation-reduction mechanism involving the NAD+ cofactor, which abstracts a hydride from the substrate, facilitating the cleavage of the C-S bond. The enzyme's activity is critical for maintaining low intracellular SAH levels, thereby preventing product inhibition of methyltransferases.
Role of NAD+ Cofactor
In simple terms: A helper molecule called NAD+ is needed for the enzyme to work.
Adenosylhomocysteinase utilizes NAD+ as a cofactor, which is tightly bound to the enzyme. The NAD+ is involved in the catalytic mechanism by mediating the oxidation of the substrate's 3'-hydroxyl group, leading to the elimination of the homocysteine moiety. This mechanism is unique among hydrolases and is essential for the enzyme's function. The redox state of NAD+ can influence enzyme activity, as observed in Drosophila Ahcy, which acts as a redox sensor.
Regulation by Metabolites and Redox State
In simple terms: The enzyme's activity can be turned up or down by other molecules and the cell's redox balance.
Adenosylhomocysteinase activity is regulated by the availability of its substrate SAH and the redox state of the cell. In Drosophila, Ahcy is a redox sensor that modulates gene expression to protect against light stress-induced retinal degeneration. Additionally, hydrogen sulfide-mediated persulfidation regulates homocysteine metabolism and enhances ferroptosis in non-small cell lung cancer, implicating AHCY in redox-dependent regulation. The enzyme's activity can also be influenced by the cellular SAM/SAH ratio, as high SAH levels inhibit methyltransferases and may feedback on AHCY expression.
Interaction with Adenosine and mRNA Methylation
In simple terms: The adenosine produced by the enzyme can affect how RNA is modified.
The AHCY-adenosine complex rewires mRNA methylation to enhance fatty acid biosynthesis and tumorigenesis. This indicates that beyond its catalytic role, AHCY can interact with adenosine and influence epitranscriptomic modifications. The enzyme's product adenosine may act as a signaling molecule or be used in other metabolic pathways, linking AHCY activity to broader cellular processes such as lipid metabolism and cancer progression.
Inhibition by Small Molecules
In simple terms: Certain drugs can block the enzyme, which may be useful for therapy.
Adenosylhomocysteinase is inhibited by carbocyclic nucleosides, which are substrate analogs that bind to the active site and interfere with catalysis. More recently, baicalein has been shown to specifically suppress microsatellite instability colorectal cancer by targeting adenosylhomocysteinase to inhibit histone H3 lysine 4 trimethylation-mediated cancer stemness. These inhibitors provide tools to study the enzyme's function and potential therapeutic strategies.
Key Genes Involved in GO:0004013 adenosylhomocysteinase activity
The following genes and proteins are key players in adenosylhomocysteinase activity and its related pathways.
| Gene | Major Role | Research Relevance |
|---|---|---|
| AHCY | Encodes adenosylhomocysteinase, the enzyme catalyzing SAH hydrolysis | Central to methionine cycle; implicated in cancer, stem cell pluripotency, and redox sensing [3,6,8] |
| MAT1A | Methionine adenosyltransferase, synthesizes SAM from methionine and ATP | Regulates SAM levels, affecting AHCY substrate availability |
| MAT2A | Methionine adenosyltransferase, synthesizes SAM in extrahepatic tissues | Linked to cancer metabolism and methylation |
| MTR | Methionine synthase, remethylates homocysteine to methionine | Connects folate cycle to methionine cycle, influencing AHCY activity |
| CBS | Cystathionine beta-synthase, converts homocysteine to cystathionine | Regulates homocysteine levels, impacting AHCY product |
| BHMT | Betaine-homocysteine S-methyltransferase, remethylates homocysteine | Alternative pathway for homocysteine removal |
| GNMT | Glycine N-methyltransferase, uses SAM to methylate glycine | Inhibited by SAH, linking to AHCY |
| DNMT1 | DNA methyltransferase 1, methylates DNA | Sensitive to SAH inhibition; affected by AHCY activity |
| DNMT3A | DNA methyltransferase 3A, de novo methylation | Regulated by SAM/SAH ratio |
| H3K4me3 | Histone H3 lysine 4 trimethylation mark | Modulated by AHCY inhibition in cancer stemness |
| NFS1 | Cysteine desulfurase, involved in iron-sulfur cluster biogenesis | Linked to persulfidation and ferroptosis regulation |
| NF-κB | Transcription factor regulating inflammation | Affected by homocysteine metabolism and N-homocysteinylation |
| Ahcy (Drosophila) | Drosophila homolog of AHCY | Redox sensor protecting against light stress |
| AHCY-adenosine complex | Complex involving AHCY and adenosine | Rewires mRNA methylation for fatty acid biosynthesis |
| SAHH | Alternative name for AHCY in some organisms | Same enzymatic activity |
| MTHFR | Methylenetetrahydrofolate reductase | Folate cycle enzyme influencing methionine synthesis |
| MTRR | Methionine synthase reductase | Regenerates methionine synthase |
| AHCYL1 | AHCY-like protein 1, paralog with similar domain | Potential regulatory role in methylation |
How Is adenosylhomocysteinase activity Regulated?
Adenosylhomocysteinase activity is regulated at multiple levels. Transcriptionally, AHCY expression can be influenced by cellular demands for methylation and redox status. Metabolically, the enzyme is subject to product inhibition by adenosine and homocysteine, and its activity is sensitive to the NAD+/NADH ratio due to its NAD+ cofactor requirement. In cancer, AHCY-adenosine complex formation rewires mRNA methylation, suggesting post-translational or complex-mediated regulation. Additionally, hydrogen sulfide-mediated persulfidation can regulate homocysteine metabolism and enhance ferroptosis, implicating redox-dependent modifications of AHCY. Small molecule inhibitors like baicalein and carbocyclic nucleosides can also modulate its activity [4,7].
adenosylhomocysteinase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| AHCY | Non-small cell lung cancer (ferroptosis regulation) | A549 or H1299 KO cells; xenograft models |
| AHCY | Microsatellite instability colorectal cancer (cancer stemness) | HCT116 or SW48 KO cells; organoids |
| AHCY | Tumorigenesis and fatty acid biosynthesis | MDA-MB-231 or HeLa KO cells; lipidomics |
| AHCY | Inflammation and homocysteine metabolism | Macrophage KO cells; LPS-induced inflammation models |
| Ahcy (Drosophila) | Light-induced retinal degeneration | Drosophila Ahcy mutants; ERG recordings |
Cancer
Adenosylhomocysteinase activity is increasingly linked to cancer. In non-small cell lung cancer, hydrogen sulfide-mediated persulfidation regulates homocysteine metabolism and enhances ferroptosis, suggesting AHCY plays a role in redox balance and cell death. The AHCY-adenosine complex rewires mRNA methylation to enhance fatty acid biosynthesis and tumorigenesis, highlighting a metabolic-epitranscriptomic axis. In microsatellite instability colorectal cancer, baicalein targets AHCY to inhibit histone H3 lysine 4 trimethylation-mediated cancer stemness, indicating AHCY as a therapeutic target.
Inflammation and Metabolic Disorders
Homocysitaconate controls inflammation through reshaping methionine metabolism and N-homocysteinylation, a process that involves AHCY and homocysteine. Dysregulated homocysteine metabolism is associated with cardiovascular and neurological disorders, and AHCY activity influences homocysteine levels. Thus, AHCY may be a modulator of inflammatory and metabolic diseases.
Retinal Degeneration
In Drosophila, Ahcy acts as a redox sensor that modulates gene expression to protect against light stress-induced retinal degeneration. This suggests that AHCY's redox-sensing function is important for neuronal survival and may have implications for human retinal diseases.
Embryonic Development and Pluripotency
Adenosylhomocysteinase plays multiple roles in maintaining the identity and pluripotency of mouse embryonic stem cells. Disruption of AHCY activity could affect developmental processes and stem cell function, linking to developmental disorders.
From adenosylhomocysteinase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| What is the effect of AHCY loss on global methylation? | AHCY knockout cell lines (e.g., HEK293T, HeLa) followed by LC-MS for SAM/SAH and methylation arrays |
| How does AHCY point mutation affect catalytic activity? | CRISPR point mutation (e.g., NAD+ binding site) in AHCY, followed by enzymatic assays |
| Does AHCY interact with adenosine to regulate mRNA methylation? | Knock-in of tagged AHCY (e.g., FLAG) for immunoprecipitation and m6A sequencing |
| Can AHCY overexpression drive tumorigenesis? | Overexpression of AHCY in cancer cell lines, followed by proliferation and xenograft assays |
| What is the role of AHCY in stem cell pluripotency? | AHCY knockout mouse embryonic stem cells, followed by pluripotency marker analysis |
| How does AHCY redox sensing protect against retinal degeneration? | Drosophila Ahcy mutants with light stress, followed by transcriptomics |
How to Study the adenosylhomocysteinase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| LC-MS metabolomics | Quantification of SAM, SAH, adenosine, homocysteine | Assessing AHCY activity in cells and tissues [1,3] |
| Enzymatic coupled assay | AHCY catalytic activity | Kinetic studies and inhibitor screening |
| RNA-seq | Global gene expression changes | Identifying pathways affected by AHCY KO |
| m6A-seq | mRNA methylation sites | Linking AHCY to epitranscriptome |
| Western blot | Protein expression and modification | Validating AHCY KO or overexpression |
| Immunoprecipitation | Protein-protein interactions | Identifying AHCY complexes |
| CRISPR screening | Genome-wide fitness and synthetic lethality | Finding genes that interact with AHCY |
| Fluorescence microscopy | Subcellular localization | Visualizing AHCY dynamics |
Enzymatic Activity Assays
Adenosylhomocysteinase activity can be measured using coupled enzymatic assays that monitor the production of adenosine or homocysteine. For example, the hydrolysis of SAH can be coupled to adenosine deaminase and glutamate dehydrogenase reactions, measuring NADH consumption spectrophotometrically. Alternatively, HPLC or LC-MS can quantify SAH, adenosine, and homocysteine directly.
CRISPR-Cas9 Genome Editing
CRISPR-Cas9 is used to generate AHCY knockout, point mutation, knock-in, and overexpression models. Knockout cells are created by introducing indels in the AHCY gene, leading to loss of enzyme activity. Point mutations can be introduced to study catalytic residues or regulatory sites. Knock-in of tags (e.g., FLAG, GFP) allows for localization and interaction studies. Overexpression is achieved by inserting the AHCY coding sequence under a strong promoter [3,4,6].
Omics Approaches
Transcriptomics (RNA-seq) and proteomics can reveal global changes in gene expression and protein abundance upon AHCY modulation. Methylation-specific techniques, such as m6A-seq and MeDIP-seq, assess changes in RNA and DNA methylation, respectively. Metabolomics via LC-MS quantifies metabolites like SAM, SAH, adenosine, and homocysteine.
Imaging and Localization
Fluorescence microscopy of GFP-tagged AHCY can determine its subcellular localization and dynamics. Live-cell imaging can track AHCY in response to redox changes or drug treatment. Immunohistochemistry of patient samples can assess AHCY expression levels in tissues.
How CRISPR Can Be Used to Study GO:0004013 adenosylhomocysteinase activity
Knockout
CRISPR knockout of AHCY is used to completely ablate adenosylhomocysteinase activity, leading to elevated SAH levels and inhibition of methyltransferases. This model is valuable for studying the enzyme's role in methylation, stem cell pluripotency, and cancer cell proliferation. Knockout cells can be analyzed by metabolomics, transcriptomics, and phenotypic assays.
Point Mutation
Point mutations in AHCY can be introduced to dissect catalytic residues or regulatory sites. For example, mutating the NAD+ binding site can abolish enzymatic activity without affecting protein stability, allowing separation of catalytic and non-catalytic functions. Such models help identify specific residues critical for substrate binding or redox sensing.
Knock-in
Knock-in of epitope tags (e.g., FLAG, HA, GFP) into the endogenous AHCY locus enables studies of protein localization, interaction, and dynamics under native expression levels. Tagged AHCY can be immunoprecipitated to identify binding partners, such as the AHCY-adenosine complex. Knock-in of disease-associated mutations can model human disorders.
Overexpression
Overexpression of AHCY via CRISPR activation or lentiviral delivery is used to study gain-of-function effects, such as enhanced tumorigenesis and fatty acid biosynthesis. Overexpression models can reveal how excess AHCY activity alters methylation potential and metabolic flux, providing insights into its oncogenic role.
How EDITGENE Supports adenosylhomocysteinase activity Research
Researchers studying adenosylhomocysteinase activity-related genes often need to determine whether a candidate gene is causally involved in a specific phenotype, such as cancer progression or stem cell maintenance. EDITGENE provides comprehensive CRISPR-based services to generate precisely engineered cell models, enabling functional validation of AHCY and its interacting partners.
Contact EDITGENE today to design your custom CRISPR model for adenosylhomocysteinase activity research.
Frequently Asked Questions About adenosylhomocysteinase activity
What is adenosylhomocysteinase activity?
Adenosylhomocysteinase activity (GO:0004013) is the enzymatic function that catalyzes the hydrolysis of S-adenosyl-L-homocysteine (SAH) to adenosine and L-homocysteine, a key step in the methionine cycle.
What genes are involved in adenosylhomocysteinase activity?
The primary gene is AHCY, which encodes the enzyme adenosylhomocysteinase. Other related genes include MAT1A, MAT2A, MTR, CBS, and BHMT, which are part of the methionine cycle.
What is the role of AHCY in cancer?
AHCY supports tumorigenesis by rewiring mRNA methylation and fatty acid biosynthesis, and its inhibition can suppress cancer stemness in colorectal cancer [3,4]. It also regulates ferroptosis in lung cancer.
How is adenosylhomocysteinase activity regulated?
It is regulated by substrate availability, NAD+/NADH ratio, redox state, and small molecule inhibitors. In Drosophila, Ahcy acts as a redox sensor. Persulfidation also regulates homocysteine metabolism.
What diseases are associated with adenosylhomocysteinase dysfunction?
Dysfunction is linked to cancers (lung, colorectal), inflammation, retinal degeneration, and developmental defects due to impaired stem cell pluripotency [1,2,3,4,6,8].
What are the substrates and products of adenosylhomocysteinase?
The substrate is S-adenosyl-L-homocysteine (SAH) and water; the products are adenosine and L-homocysteine.
How can I study adenosylhomocysteinase activity in the lab?
You can use enzymatic assays, LC-MS metabolomics, CRISPR knockout/knock-in models, RNA-seq, and m6A-seq to measure activity and downstream effects [3,5].
What is the relationship between AHCY and methylation?
AHCY removes SAH, a potent inhibitor of methyltransferases, thereby maintaining the SAM/SAH ratio and supporting DNA, RNA, and histone methylation.
Are there inhibitors of adenosylhomocysteinase?
Yes, carbocyclic nucleosides and baicalein are known inhibitors. Baicalein specifically targets AHCY in colorectal cancer [4,7].
What model organisms are used to study AHCY?
Mouse embryonic stem cells, Drosophila melanogaster, and various human cancer cell lines are commonly used [6,8,3].
Conclusion
Adenosylhomocysteinase activity (GO:0004013) is a central enzymatic function in the methionine cycle, controlling methylation potential and influencing diverse biological processes from stem cell pluripotency to cancer progression. Its dysregulation is implicated in inflammation, retinal degeneration, and multiple cancers, making it a promising therapeutic target. Advances in CRISPR genome editing and omics technologies are accelerating our understanding of AHCY's molecular mechanisms and disease relevance. EDITGENE's suite of CRISPR services empowers researchers to create precise models for studying adenosylhomocysteinase activity and developing novel interventions.
References
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- 2. Zheng H et al.. 2024. Hydrogen sulfide-mediated persulfidation regulates homocysteine metabolism and enhances ferroptosis in non-small cell lung cancer.. Mol Cell 84(20):4016-4030.e6 PMID: 39321805
- 3. Liao K et al.. 2026. The AHCY-adenosine complex rewires mRNA methylation to enhance fatty acid biosynthesis and tumorigenesis.. Cell Res 36(2):152-172 PMID: 41549122
- 4. Zheng Y et al.. 2025. Baicalein specifically suppresses microsatellite instability colorectal cancer by targeting adenosylhomocysteinase to inhibit histone H3 lysine 4 trimethylation-mediated cancer stemness.. Phytomedicine 148:157291 PMID: 41038143
- 5. Chiang PK et al.. 1996. S-Adenosylmethionine and methylation.. FASEB J 10(4):471-80 PMID: 8647346
- 6. Jiang Q et al.. 2024. Adenosylhomocysteinase plays multiple roles in maintaining the identity and pluripotency of mouse embryonic stem cells†.. Biol Reprod 110(3):450-464 PMID: 38035769
- 7. Marquez VE et al.. 1986. Carbocyclic nucleosides.. Med Res Rev 6(1):1-40 PMID: 3512934
- 8. Stanhope SC et al.. 2025. Drosophila Ahcy is a redox sensor that modulates gene expression to protect against light stress-induced retinal degeneration.. Proc Natl Acad Sci U S A 122(38):e2511388122 PMID: 40971386
