GO:0008453 L-alanine:glyoxylate transaminase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0008453 describes the molecular function that catalyzes the reversible conversion of L-alanine and glyoxylate to pyruvate and glycine.
• The enzyme is best known as alanine-glyoxylate aminotransferase (AGT), which in humans is encoded by AGXT and is primarily localized to peroxisomes in hepatocytes.
• Deficiency or mistargeting of AGT activity causes primary hyperoxaluria type I, a severe metabolic disorder leading to oxalate kidney stones and renal failure.
• The activity is also present in mitochondria and cytosol of liver and kidney, where it participates in gluconeogenesis and amino acid metabolism.
• In plants, alanine aminotransferase and glycine aminotransferase homologs perform similar transamination reactions, linking photorespiration and nitrogen metabolism.
• Research on this activity employs spectrophotometric and HPLC-based enzyme assays, subcellular fractionation, and CRISPR-based models to dissect its physiological roles.
Description
L-alanine:glyoxylate transaminase activity (GO:0008453) is a molecular function that catalyzes the reversible transfer of an amino group from L-alanine to glyoxylate, yielding pyruvate and glycine. This reaction is a key step in the detoxification of glyoxylate and in the interconversion of amino acids, linking carbohydrate and amino acid metabolism. The enzyme responsible, alanine-glyoxylate aminotransferase (AGT), is highly expressed in the liver and kidney of mammals, where it is found in peroxisomes and mitochondria. In humans, AGT is encoded by the AGXT gene, and its correct subcellular localization is critical for preventing the accumulation of glyoxylate, which would otherwise be oxidized to oxalate. The clinical importance of this activity is underscored by primary hyperoxaluria type I, an inherited disorder caused by mutations in AGXT that lead to deficient or mistargeted enzyme activity. Beyond disease, the reaction contributes to gluconeogenesis from glyoxylate and to nitrogen recycling in plants. Understanding the catalytic mechanism, regulation, and physiological roles of GO:0008453 is therefore relevant to metabolic biochemistry, nephrology, and plant physiology. This article integrates authoritative QuickGO data with verified PubMed literature to provide a comprehensive overview of the term, its associated genes, and experimental approaches for studying it.
L-alanine:glyoxylate transaminase activity At A Glance
| GO ID | GO:0008453 |
|---|---|
| GO term | L-alanine:glyoxylate transaminase activity |
| Ontology | molecular_function |
| Synonym | AGT activity; alanine--glyoxylate aminotransferase activity; alanine-glyoxylate transaminase activity; L-alanine:glyoxylate aminotransferase activity |
| Major function | Catalyzes the reversible transamination of L-alanine and glyoxylate to pyruvate and glycine |
| Cofactor | Pyridoxal phosphate (PLP) |
| Subcellular localization | Peroxisomes, mitochondria, and cytosol (tissue-dependent) |
| Key enzyme | Alanine-glyoxylate aminotransferase (AGT), encoded by AGXT in humans |
| Associated disease | Primary hyperoxaluria type I (PH1) |
What Is GO:0008453?
GO:0008453, L-alanine:glyoxylate transaminase activity, is defined as the catalysis of the reaction: L-alanine + glyoxylate = pyruvate + glycine. This is a transamination reaction in which the amino group of L-alanine is transferred to glyoxylate, producing glycine and pyruvate. The activity requires pyridoxal phosphate (PLP) as a cofactor and is reversible. It is classified as a molecular function and is synonymous with alanine-glyoxylate aminotransferase (AGT) activity, among other names.
Why Is L-alanine:glyoxylate transaminase activity Important in Cell Biology?
GO:0008453 is critical for metabolic homeostasis because it removes glyoxylate, a reactive metabolite that can be converted to oxalate, which is insoluble and forms kidney stones. In humans, deficiency or mistargeting of AGT activity causes primary hyperoxaluria type I, a devastating disease characterized by recurrent calcium oxalate nephrolithiasis and progressive renal failure. The activity also participates in gluconeogenesis and amino acid metabolism, linking alanine and glyoxylate to central carbon pathways. In plants, homologous enzymes contribute to photorespiration and nitrogen assimilation. Therefore, understanding this activity has implications for human health, metabolic engineering, and comparative biochemistry.
• Prevents glyoxylate accumulation and oxalate production, protecting against kidney stone formation.
• Deficiency or mistargeting of AGT causes primary hyperoxaluria type I, a rare but severe inherited disorder.
• Participates in gluconeogenesis by converting glyoxylate to glycine and pyruvate, which can enter the TCA cycle.
• Contributes to amino acid metabolism and nitrogen balance in liver and kidney.
• Provides a model for studying protein mistargeting due to point mutations that activate cryptic targeting sequences.
• Enzyme activity assays are used clinically to diagnose hyperoxaluria type I.
• In plants, similar transaminases are involved in photorespiration and nitrogen recycling.
• The enzyme's dual localization (peroxisome vs. mitochondria) is regulated by genetic and metabolic factors.
• It is a target for therapeutic strategies aiming to reduce oxalate production in hyperoxaluria.
• Research on this activity informs protein engineering and drug development for metabolic diseases.
Molecular Mechanism of L-alanine:glyoxylate transaminase activity
Substrate Binding and Transamination
In simple terms: The enzyme grabs alanine and glyoxylate and swaps an amino group between them.
The catalytic mechanism follows a ping-pong bi-bi kinetic pattern typical of pyridoxal phosphate (PLP)-dependent transaminases. First, L-alanine binds to the enzyme-PLP complex, forming a Schiff base with the cofactor. The amino group is transferred to PLP, yielding pyridoxamine phosphate (PMP) and releasing pyruvate. Then, glyoxylate binds and accepts the amino group from PMP, producing glycine and regenerating the PLP-enzyme. This reversible reaction is essential for maintaining the balance of these metabolites.
Cofactor Requirement and Catalytic Residues
In simple terms: A vitamin B6 derivative helps the enzyme transfer amino groups.
The enzyme requires pyridoxal phosphate (PLP) as an essential cofactor. The PLP molecule is covalently bound to a conserved lysine residue in the active site, forming an internal aldimine. During catalysis, the lysine is displaced by the amino group of L-alanine, forming an external aldimine. Key catalytic residues, including the lysine and an aspartate, facilitate proton transfer and stabilize reaction intermediates. Mutations in these residues abolish activity, as observed in patients with primary hyperoxaluria type I.
Subcellular Localization and Targeting
In simple terms: The enzyme can be sent to different compartments inside the cell, which affects its function.
In humans, AGT is predominantly localized to peroxisomes in hepatocytes, but a point mutation can activate a cryptic mitochondrial targeting sequence, causing mistargeting to mitochondria. This mistargeting is a hallmark of primary hyperoxaluria type I. The peroxisomal targeting is mediated by a C-terminal PTS1 signal, while the mitochondrial targeting sequence is N-terminal and normally masked. The balance between these targeting signals determines the enzyme's subcellular distribution and its access to substrates.
Tissue Distribution and Isoforms
In simple terms: Different organs have different versions of this enzyme.
L-alanine:glyoxylate transaminase activity is found in liver, kidney, and other tissues. In rat liver, the enzyme is present in both peroxisomes and mitochondria, with distinct isoforms. In rat kidney and liver mitochondria, a separate enzyme, AGT II, possesses cysteine S-conjugate beta-lyase activity, linking it to the metabolism of halogenated alkenes and potential nephrotoxicity. These tissue-specific isoforms contribute to diverse metabolic roles.
Kinetic Properties and Regulation
In simple terms: The enzyme's speed and efficiency can be measured and are influenced by conditions.
The enzyme exhibits Michaelis-Menten kinetics with respect to both substrates. The reaction is reversible, but under physiological conditions, the removal of glyoxylate is favored. Enzyme activity can be regulated by substrate availability, cofactor levels, and hormonal signals. For example, gluconeogenic hormones may influence the expression of the enzyme to support glucose production from glyoxylate. Additionally, the enzyme's activity is sensitive to pH and temperature, which is important for assay design.
Key Genes Involved in GO:0008453 L-alanine:glyoxylate transaminase activity
The following genes encode enzymes or related proteins that exhibit L-alanine:glyoxylate transaminase activity or are directly involved in its metabolic pathways.
| Gene | Major Role | Research Relevance |
|---|---|---|
| AGXT | Encodes human alanine-glyoxylate aminotransferase, the primary enzyme for GO:0008453 | Mutations cause primary hyperoxaluria type I; target for gene therapy |
| AGXT2 | Encodes alanine-glyoxylate aminotransferase 2, a mitochondrial enzyme with broader substrate specificity | Involved in amino acid metabolism and detoxification |
| GPT | Encodes glutamate pyruvate transaminase (alanine aminotransferase), which can also use glyoxylate as a substrate | Marker of liver injury; potential off-target in assays |
| GPT2 | Encodes a mitochondrial alanine aminotransferase | Related to gluconeogenesis and amino acid metabolism |
| SHMT1 | Serine hydroxymethyltransferase, interconverts serine and glycine | Linked to glycine metabolism and one-carbon cycle |
| SHMT2 | Mitochondrial serine hydroxymethyltransferase | Provides glycine for mitochondrial metabolism |
| GLDC | Glycine decarboxylase, part of the glycine cleavage system | Defects cause non-ketotic hyperglycinemia; interacts with glyoxylate metabolism |
| HOGA1 | 4-hydroxy-2-oxoglutarate aldolase, involved in glyoxylate metabolism | Mutations cause primary hyperoxaluria type III |
| GRHPR | Glyoxylate reductase/hydroxypyruvate reductase, reduces glyoxylate to glycolate | Mutations cause primary hyperoxaluria type II |
| LDHA | Lactate dehydrogenase A, converts pyruvate to lactate | Indirectly linked to pyruvate produced by GO:0008453 |
| PC | Pyruvate carboxylase, converts pyruvate to oxaloacetate | Gluconeogenic enzyme using pyruvate from transamination |
| GOT1 | Glutamate oxaloacetate transaminase 1, cytosolic | Aminotransferase related to nitrogen metabolism |
| GOT2 | Glutamate oxaloacetate transaminase 2, mitochondrial | Participates in malate-aspartate shuttle |
| PSAT1 | Phosphoserine aminotransferase, uses pyridoxal phosphate | Serine biosynthesis, related transamination |
| PSPH | Phosphoserine phosphatase | Serine biosynthesis, links to glycine |
| MAO | Monoamine oxidase, produces hydrogen peroxide | May influence oxidative stress in peroxisomes |
| CAT | Catalase, detoxifies hydrogen peroxide in peroxisomes | Protects AGT from oxidative damage |
| PEX5 | Peroxisomal targeting signal 1 receptor | Required for peroxisomal import of AGT |
How Is L-alanine:glyoxylate transaminase activity Regulated?
The activity of L-alanine:glyoxylate transaminase is regulated at multiple levels. Transcriptional regulation of AGXT is influenced by metabolic and hormonal signals, including glucocorticoids and glucagon, which promote gluconeogenesis. The enzyme's subcellular localization is controlled by the balance of targeting signals; a point mutation can shift localization from peroxisomes to mitochondria, as seen in primary hyperoxaluria type I. Post-translational modifications, such as phosphorylation, may affect enzyme activity, although specific sites remain to be fully characterized. Additionally, the availability of cofactor PLP and substrates (L-alanine and glyoxylate) directly impacts reaction rate. In plants, light and nitrogen availability regulate homologous enzyme expression.
L-alanine:glyoxylate transaminase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| AGXT | Primary hyperoxaluria type I | AGXT knockout mice; patient-derived iPSCs; knock-in of G170R mutation |
| GRHPR | Primary hyperoxaluria type II | GRHPR knockout mice; cell models for oxalate production |
| HOGA1 | Primary hyperoxaluria type III | HOGA1 knockout mice; hepatocyte cell lines |
| AGXT2 | Halogenated alkene toxicity | AGT2 knockout rats; mitochondrial assays |
| SHMT1/2 | Glycine metabolism disorders | Knockout cell lines; metabolic flux analysis |
Primary Hyperoxaluria Type I
Primary hyperoxaluria type I (PH1) is an autosomal recessive disorder caused by mutations in AGXT, leading to deficient or mistargeted L-alanine:glyoxylate transaminase activity. The enzyme normally detoxifies glyoxylate in peroxisomes; when defective, glyoxylate is converted to oxalate, which forms insoluble calcium oxalate crystals in the kidneys and urinary tract. This results in recurrent kidney stones, nephrocalcinosis, and progressive renal failure. Some mutations, such as the common G170R, cause mistargeting of AGT to mitochondria, where it cannot access glyoxylate efficiently. Diagnosis relies on measuring enzyme activity in liver biopsy or genetic testing.
Hyperoxaluria Type II and III
Mutations in GRHPR cause primary hyperoxaluria type II, characterized by deficiency of glyoxylate reductase/hydroxypyruvate reductase, which also leads to glyoxylate accumulation and oxalate production. Primary hyperoxaluria type III is caused by mutations in HOGA1, encoding 4-hydroxy-2-oxoglutarate aldolase, which affects glyoxylate metabolism. Although these disorders do not directly involve GO:0008453, they highlight the importance of the glyoxylate detoxification pathway in which AGT participates.
Nephrotoxicity and Hepatotoxicity of Halogenated Alkenes
L-alanine-glyoxylate aminotransferase II (AGT II) in rat kidney and liver mitochondria possesses cysteine S-conjugate beta-lyase activity, which can bioactivate halogenated alkenes to toxic metabolites. This contributes to the nephrotoxicity and hepatotoxicity of compounds such as trichloroethylene. Thus, GO:0008453-related enzymes can play a role in xenobiotic metabolism and chemical toxicity.
Plant Metabolism and Photorespiration
In plants, alanine aminotransferase and glycine aminotransferase homologs participate in photorespiration and nitrogen recycling. While not directly linked to human disease, these enzymes are important for crop productivity and stress responses. Understanding their regulation could inform agricultural biotechnology.
From L-alanine:glyoxylate transaminase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of AGXT cause glyoxylate accumulation and oxalate stones? | AGXT knockout mouse (KO) |
| How does the G170R mutation affect subcellular localization? | Knock-in of G170R in HepG2 cells or mice |
| Can overexpression of AGXT rescue hyperoxaluria? | AAV-mediated AGXT overexpression in KO mice |
| What is the role of AGXT2 in xenobiotic metabolism? | AGXT2 knockout rat or human cell lines |
| How does AGT activity change during gluconeogenesis? | Primary hepatocytes with hormonal treatment |
| Can CRISPR activation increase AGXT expression? | dCas9-VP64 activation in hepatocytes |
How to Study the L-alanine:glyoxylate transaminase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Spectrophotometric assay | Enzyme activity via NADH oxidation | Clinical diagnosis of PH1 |
| HPLC | Glycine or pyruvate concentration | Enzyme kinetics and diagnosis |
| Subcellular fractionation | Localization of AGT in organelles | Studying mistargeting in PH1 |
| Immunofluorescence | Subcellular distribution of tagged AGT | Visualizing peroxisomal vs mitochondrial targeting |
| CRISPR knockout | Loss-of-function phenotype | Modeling PH1 in mice or cells |
| RNA-seq | Transcriptional changes upon AGT loss | Identifying compensatory pathways |
| 13C metabolic flux | Flux through transamination | Quantifying gluconeogenesis |
| Enzyme-linked immunosorbent assay | Protein levels of AGT | Validating expression in models |
Enzyme Activity Assays
L-alanine:glyoxylate transaminase activity is typically measured using spectrophotometric methods that couple the production of pyruvate to lactate dehydrogenase and NADH oxidation, monitored at 340 nm. Alternatively, high-performance liquid chromatography (HPLC) can quantify glycine or pyruvate directly. These assays are used for clinical diagnosis of hyperoxaluria type I and for characterizing enzyme kinetics.
Subcellular Fractionation and Imaging
To determine the subcellular localization of AGT, researchers use differential centrifugation and density gradient fractionation of liver homogenates, followed by enzyme activity assays or immunoblotting. Fluorescence microscopy with tagged AGT (e.g., GFP) can visualize peroxisomal versus mitochondrial targeting in cultured cells.
Genetic and Genomic Approaches
CRISPR-Cas9 knockout of AGXT in cell lines or mice allows study of loss-of-function phenotypes. Knock-in of patient mutations (e.g., G170R) recapitulates mistargeting. RNA-seq and proteomics can reveal global metabolic changes. In plants, homologous genes can be edited to study photorespiration.
Metabolic Flux Analysis
Isotope tracing with 13C-labeled alanine or glyoxylate can quantify flux through the transamination reaction in cells or perfused organs. This approach links GO:0008453 activity to gluconeogenesis and amino acid metabolism.
How CRISPR Can Be Used to Study GO:0008453 L-alanine:glyoxylate transaminase activity
Knockout
CRISPR-Cas9 knockout of AGXT in human hepatocyte cell lines (e.g., HepG2) or mouse models abolishes L-alanine:glyoxylate transaminase activity, leading to glyoxylate accumulation and oxalate production. These models mimic primary hyperoxaluria type I and are used to test therapeutic interventions.
Point Mutation
Knock-in of the common G170R mutation in AGXT using CRISPR-Cas9 and homology-directed repair recapitulates the mistargeting of AGT to mitochondria, a hallmark of PH1. This model is valuable for studying the molecular basis of mistargeting and for screening correctors.
Knock-in
Tagged knock-in of AGXT with fluorescent proteins (e.g., GFP) allows real-time imaging of enzyme localization and dynamics in live cells. This approach can be combined with organelle markers to quantify peroxisomal versus mitochondrial distribution.
Overexpression
CRISPR activation (CRISPRa) or lentiviral overexpression of AGXT can increase enzyme activity and reduce oxalate production in cellular models of PH1. Overexpression in mouse liver via AAV vectors is a potential gene therapy strategy.
How EDITGENE Supports L-alanine:glyoxylate transaminase activity Research
Researchers studying L-alanine:glyoxylate transaminase activity-related genes often need to determine whether a candidate gene is causally involved in glyoxylate detoxification, amino acid metabolism, or disease pathogenesis. EDITGENE provides comprehensive CRISPR-based services to create precise cell and animal models, enabling functional validation of genes like AGXT and its regulators.
Contact EDITGENE today to design your custom CRISPR model for L-alanine:glyoxylate transaminase activity research.
Frequently Asked Questions About L-alanine:glyoxylate transaminase activity
What is L-alanine:glyoxylate transaminase activity?
It is the enzymatic activity (GO:0008453) that catalyzes the reversible conversion of L-alanine and glyoxylate to pyruvate and glycine, using pyridoxal phosphate as a cofactor.
What genes are involved in L-alanine:glyoxylate transaminase activity?
The primary gene is AGXT, encoding alanine-glyoxylate aminotransferase. Related genes include AGXT2, GPT, GPT2, and GRHPR, which participate in glyoxylate and amino acid metabolism.
What diseases are associated with L-alanine:glyoxylate transaminase activity?
Deficiency or mistargeting of AGT causes primary hyperoxaluria type I, characterized by kidney stones and renal failure. Other hyperoxalurias involve related genes.
How is L-alanine:glyoxylate transaminase activity measured?
It is measured using spectrophotometric assays coupling pyruvate production to NADH oxidation, or by HPLC quantification of glycine or pyruvate.
Where is L-alanine:glyoxylate transaminase located in the cell?
In humans, it is primarily peroxisomal in hepatocytes, but can be mitochondrial or cytosolic depending on the tissue and isoform.
What is the role of AGXT in primary hyperoxaluria type I?
Mutations in AGXT reduce or mistarget the enzyme, leading to glyoxylate accumulation and oxalate production, which damages kidneys.
Can CRISPR be used to study L-alanine:glyoxylate transaminase activity?
Yes, CRISPR knockout, knock-in, and activation models allow precise manipulation of AGXT and related genes to study function and disease.
What are the substrates of L-alanine:glyoxylate transaminase?
The substrates are L-alanine and glyoxylate; the products are pyruvate and glycine.
Is L-alanine:glyoxylate transaminase activity reversible?
Yes, the reaction is reversible, but in vivo it primarily detoxifies glyoxylate by converting it to glycine.
What model organisms are used to study L-alanine:glyoxylate transaminase activity?
Mouse models (e.g., Agxt knockout), rat liver fractions, and plant systems like maize are used to study this activity.
Conclusion
L-alanine:glyoxylate transaminase activity (GO:0008453) is a fundamental metabolic function that safeguards against glyoxylate toxicity and contributes to amino acid and carbohydrate metabolism. Its clinical relevance is highlighted by primary hyperoxaluria type I, where mutations in AGXT lead to enzyme deficiency or mistargeting. Ongoing research using CRISPR models and advanced biochemical assays continues to unravel the regulation and therapeutic potential of this activity. Understanding GO:0008453 not only informs disease mechanisms but also provides insights into evolutionarily conserved metabolic pathways.
References
- 1. Cooper AJ et al.. 2003. L-alanine-glyoxylate aminotransferase II of rat kidney and liver mitochondria possesses cysteine S-conjugate beta-lyase activity: a contributing factor to the nephrotoxicity/hepatotoxicity of halogenated alkenes?. Biochem J 376(Pt 1):169-78 PMID: 12859250
- 2. Wanders RJ et al.. 1990. Human liver L-alanine-glyoxylate aminotransferase: characteristics and activity in controls and hyperoxaluria type I patients using a simple spectrophotometric method.. Clin Chim Acta 189(2):139-44 PMID: 2397596
- 3. Rowsell EV et al.. 1969. Liver-L-alanine-glyoxylate and L-serine-pyruvate aminotransferase activities: an apparent association with gluconeogenesis.. Biochem J 115(5):1071-3 PMID: 5360676
- 4. Petrarulo M et al.. 1992. High-performance liquid chromatographic microassay for L-alanine:glyoxylate aminotransferase activity in human liver.. Clin Chim Acta 208(3):183-92 PMID: 1499137
- 5. Purdue PE et al.. 1991. Mistargeting of peroxisomal L-alanine:glyoxylate aminotransferase to mitochondria in primary hyperoxaluria patients depends upon activation of a cryptic mitochondrial targeting sequence by a point mutation.. Proc Natl Acad Sci U S A 88(23):10900-4 PMID: 1961759
- 6. Nakatani T et al.. 1985. Peroxisome localized human hepatic alanine-glyoxylate aminotransferase and its application to clinical diagnosis.. Clin Biochem 18(5):311-6 PMID: 4053344
- 7. Rowsell EV et al.. 1972. The subcellular distribution of rat liver L-alanine-glyoxylate aminotransferase in relation to a pathway for glucose formation involving glyoxylate.. Biochem J 127(1):155-65 PMID: 5073739
- 8. Orzechowski S et al.. 1999. Alanine aminotransferase and glycine aminotransferase from maize (Zea mays L.) leaves.. Acta Biochim Pol 46(2):447-57 PMID: 10547044
