Oxaloacetic Acid
Properties
| State | Solid (white to pale yellow crystalline powder; unstable) |
| Color | White to pale yellow |
| Solubility | Soluble in water; spontaneously decarboxylates to pyruvate in solution |
| Melting Point | 161 °C (decomposes) |
| Boiling Point | Decomposes before boiling |
About Oxaloacetic Acid
Oxaloacetic acid (OAA, oxaloacetate at physiological pH) is a 4-carbon dicarboxylic alpha-ketoacid with the formula C4H4O5 and a molar mass of 132.071 g/mol. It sits at the busiest intersection in central metabolism. Citrate synthase grabs OAA, condenses it with acetyl-CoA, and starts the citric acid cycle — and after one full turn, OAA is regenerated. That regeneration is what makes the TCA cycle catalytic with respect to oxaloacetate: a single OAA molecule can shuttle through the cycle thousands of times, oxidizing acetyl-CoA after acetyl-CoA. OAA is also the substrate that PEP carboxykinase (PEPCK) phosphorylates and decarboxylates to make phosphoenolpyruvate, the committed step of gluconeogenesis. It is the keto partner of aspartate (one transamination away), the input to the malate-aspartate shuttle that moves cytosolic NADH into mitochondria, and the anaplerotic refill point that pyruvate carboxylase produces from pyruvate and CO2 when cycle intermediates run low. Chemically, free OAA is unstable — the beta-keto acid spontaneously decarboxylates to pyruvate plus CO2 on the bench, with a half-life of hours at room temperature in aqueous solution. Cells get away with it because steady-state OAA in mitochondria is held below 10 micromolar.
Where you'll encounter it
If you've ever measured aspartate aminotransferase (AST) on a clinical chemistry panel, you measured OAA chemistry — the assay couples the AST-catalyzed transfer of the alpha-amino group from aspartate to alpha-ketoglutarate (which produces oxaloacetate) to malate dehydrogenase running in reverse, consuming NADH whose absorbance drop at 340 nm gives the rate. Cardiac troponin replaced AST as the preferred MI marker, but the chemistry is still in every clinical analyzer for liver function panels. In a research biochem lab, you store OAA stock solutions on ice and use them within an hour because they decarboxylate as you watch. Metabolic flux analysis with 13C-labeled OAA tracers has become the standard way to map cancer-cell rewiring of the TCA cycle, particularly the reductive carboxylation pathway that hypoxic tumors use to make citrate from glutamine.
Common Uses
- Substrate for citrate synthase in the citric acid cycle (TCA condensation step)
- Gateway substrate for gluconeogenesis through PEP carboxykinase (PEPCK)
- Anaplerotic product of pyruvate carboxylase, refilling depleted TCA intermediates
- Coupled-enzyme assay component for clinical AST measurement and lactate dehydrogenase studies
- Tracer substrate in 13C metabolic flux analysis of cancer and hypoxia metabolism
Safety Information
Non-toxic at the concentrations seen in cells. Bench-grade OAA can cause mild skin and eye irritation from its acidity. GHS: H315 (skin irritation), H319 (eye irritation). The bigger handling issue is chemical instability — solid OAA must be stored desiccated at -20 °C and solutions must be made fresh in cold buffer and used within an hour. Decomposition products (pyruvate and CO2) are themselves harmless but make stock concentrations unreliable for kinetics work if you let the bottle warm up.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.