What Is CA5A? Gene, Protein, and Isoenzyme Context

Carbonic anhydrase VA (CA5A) is a member of the α-carbonic anhydrase family, a group of zinc-containing metalloenzymes that catalyze one of the fastest known enzymatic reactions: the reversible hydration of carbon dioxide (CO₂ + H₂O ⇌ HCO₃⁻ + H⁺). The human genome encodes at least 15 catalytically active CA isoenzymes, each distinguished by tissue distribution, subcellular localization, and kinetic properties.

CA5A is encoded by the CA5A gene and is one of only two mitochondrially targeted isoforms in humans, the other being CA5B. The CA5A protein contains an N-terminal mitochondrial targeting sequence that directs it to the mitochondrial matrix, where it supplies bicarbonate required for several anabolic pathways. Unlike cytosolic isoforms such as CA1 and CA2, CA5A's exclusive mitochondrial localization makes it a critical node in organelle-level carbon metabolism.

Recombinant Human CA5A Protein produced for research applications allows investigators to study the enzyme's catalytic mechanism, screen for isoform-selective inhibitors, and probe its role in disease-associated metabolic reprogramming without the need to isolate the native protein from mitochondria-rich tissues.

Biological Functions and Metabolic Significance

The primary biochemical role of CA5A is to maintain an adequate supply of bicarbonate (HCO₃⁻) within the mitochondrial matrix. Bicarbonate is an obligatory substrate for three key carboxylation reactions catalyzed by biotin-dependent enzymes:

• Carbamoyl phosphate synthetase I (CPS1): The rate-limiting step of the urea cycle, requiring bicarbonate to initiate nitrogen disposal.
• Pyruvate carboxylase (PC): Converts pyruvate to oxaloacetate, replenishing TCA cycle intermediates and supporting gluconeogenesis.
• Acetyl-CoA carboxylase 2 (ACC2): Involved in the regulation of mitochondrial fatty acid oxidation.

Without sufficient CA5A activity, the local concentration of bicarbonate in the mitochondrial matrix may become rate-limiting for these reactions, linking CA5A function directly to hepatic glucose output, nitrogen homeostasis, and lipid metabolism. Studies in model systems have suggested that CA5A inhibition can modulate glucose production in hepatocytes, highlighting the enzyme as a potential therapeutic target in type 2 diabetes and hyperammonemia.

Beyond its catalytic role, CA5A contributes to mitochondrial pH homeostasis by buffering proton concentrations, which is relevant to oxidative phosphorylation efficiency and overall mitochondrial membrane potential.

Research Applications of Recombinant Human CA5A Protein

Recombinant Human CA5A Protein is suitable for a range of in vitro research applications. Key uses include:

• Enzyme activity and kinetics assays: Measurement of CO₂ hydration or esterase activity using colorimetric or stopped-flow spectrophotometric methods enables characterization of CA5A kinetic parameters (Km, Vmax, kcat) and comparison across CA isoforms.
• Inhibitor screening and selectivity profiling: Because isoform-selective CA inhibitors are of pharmacological interest, recombinant CA5A serves as a key counter-screen target alongside other recombinant isoforms (CA1, CA2, CA9, CA12) to determine selectivity windows for candidate compounds.
• Structural and biophysical studies: Recombinant protein of defined purity is required for crystallography, cryo-EM, and biophysical interaction studies (e.g., surface plasmon resonance, isothermal titration calorimetry).
• Antibody validation: Defined recombinant antigen enables rigorous validation of CA5A-specific antibodies by ELISA, Western blot, and dot-blot assays.
• Metabolic pathway reconstitution: In cell-free systems, CA5A can be combined with CPS1 or pyruvate carboxylase to assess the impact of bicarbonate supply on downstream enzymatic flux.

When designing experiments, researchers should confirm that the recombinant protein preparation retains the zinc cofactor and exhibits measurable CO₂ hydration activity, as loss of zinc during purification can produce catalytically inactive protein.

Handling, Storage, and Quality Considerations

Proper handling of Recombinant Human CA5A Protein is essential to preserve catalytic activity and experimental reproducibility. General best-practice guidelines applicable to recombinant carbonic anhydrase preparations include:

• Storage temperature: Upon receipt, aliquot the protein to avoid repeated freeze-thaw cycles and store at −80 °C for long-term preservation. Short-term storage (up to one week) may be acceptable at −20 °C depending on the formulation buffer provided by the manufacturer.
• Avoid repeated freeze-thaw: Each freeze-thaw cycle risks denaturation and aggregation of the protein, leading to reduced specific activity. Single-use aliquots are strongly recommended.
• Buffer compatibility: CA inhibitors include certain anions (e.g., azide, phosphate at high concentrations). Verify that the storage or assay buffer does not contain components that interfere with zinc coordination or active-site access.
• Activity verification: Prior to use in critical experiments, confirm enzymatic activity using a validated CO₂ hydration assay or p-nitrophenyl acetate esterase assay as a functional QC step.
• Protein concentration determination: Use a method compatible with the formulation buffer (e.g., BCA assay or UV absorbance at 280 nm with the calculated extinction coefficient) to determine working concentration accurately.

Researchers should consult the product-specific datasheet provided with each lot for exact formulation, concentration, purity grade, and lot-specific activity data.

CA5A in Disease Research and Therapeutic Relevance

The metabolic centrality of CA5A has generated interest in its role in several disease contexts:

• Type 2 diabetes and gluconeogenesis: Because CA5A supplies bicarbonate to pyruvate carboxylase—an enzyme critical for hepatic gluconeogenesis—selective CA5A inhibition has been explored as a strategy to reduce fasting hyperglycemia. Preclinical data in rodent models have suggested that CA5A inhibitors can lower hepatic glucose output, although achieving sufficient isoform selectivity over the ubiquitous CA2 remains a challenge.
• Hyperammonemia and urea cycle disorders: CA5A delivers bicarbonate to CPS1, the gate-keeping enzyme of the urea cycle. Reduced CA5A activity may contribute to impaired ammonia disposal, and conversely, CA5A activation or gene therapy approaches have been discussed in the context of urea cycle deficiency research.
• Obesity and fatty acid metabolism: Given CA5A's indirect role in fatty acid synthesis via mitochondrial bicarbonate supply, its modulation may influence lipid homeostasis, making it a subject of metabolic syndrome research.
• Cancer metabolism: Metabolic reprogramming in cancer cells involves altered mitochondrial function, and differential CA isoform expression has been reported in several tumor types. CA5A expression changes in specific cancers have been noted in transcriptomic datasets, though its functional significance in oncology is an active research area.

Recombinant Human CA5A Protein from Aladdin Scientific supports these research areas by providing a well-defined, consistent enzyme source for mechanistic and translational studies.