Aspartic Acid
Properties
| State | Solid (white crystalline powder) |
| Color | White |
| Solubility | Slightly soluble in water (5.4 g/L at 25°C); soluble in dilute acids and bases |
| Melting Point | 270°C (decomposes) |
| Boiling Point | Decomposes before boiling |
About Aspartic Acid
Aspartic acid is one of the two acidic amino acids — the other is glutamic acid — and at physiological pH it exists almost entirely as the anionic aspartate, with the side-chain carboxyl deprotonated (pKa3 ≈ 3.65). Its compact four-carbon structure with carboxyls at both ends gives it an unusually central role in metabolism. Aspartate is one of the two nitrogen donors in the urea cycle (the other is ammonia), reacting with citrulline to form argininosuccinate and contributing the second nitrogen that ultimately ends up in urea. In nucleotide biosynthesis, aspartate is the source of the N1 atom in purines and contributes the entire pyrimidine ring carbon-nitrogen backbone — every cell synthesizing DNA needs aspartate continuously. As a residue in proteins, aspartate side chains often coordinate metal ions in active sites (the canonical aspartyl proteases, including HIV protease and renin, use two aspartate residues to activate water for amide-bond hydrolysis), and they participate in the catalytic triad of serine proteases like trypsin. The artificial sweetener aspartame is the methyl ester of the dipeptide L-aspartyl-L-phenylalanine, and roughly 200x sweeter than sucrose by mass — though metabolically the body hydrolyzes it back to its three components, including the aspartate.
Where you'll encounter it
If you've consumed any diet soda in the last forty years, you've consumed aspartame, which contains an aspartic acid residue that gets liberated by digestive proteases in your gut. In a biochemistry teaching lab, aspartate's role in the urea cycle is one of the canonical examples used to illustrate how amino-acid catabolism feeds nitrogen excretion: feed labeled aspartate to a hepatocyte preparation, follow the labeled nitrogen, and you'll see it appear in urea within minutes. In drug discovery, aspartyl-protease inhibitors are a major drug class — the HIV protease inhibitors (saquinavir, ritonavir, lopinavir) all target a pair of aspartate residues in the viral enzyme's active site, and the tactic is direct enough that the corresponding crystal structures appear in nearly every introductory medicinal-chemistry textbook.
Common Uses
- Urea-cycle nitrogen donor for liver-based ammonia clearance
- Building block for purine and pyrimidine nucleotide biosynthesis
- Aspartame precursor in artificial-sweetener manufacture
- Active-site residue in HIV protease and other aspartyl protease drug targets
- Excitatory neurotransmitter in select brain regions
Safety Information
GRAS for dietary use; non-toxic at the levels found in normal food and supplements. The aspartame controversy — whether the methanol released during aspartame hydrolysis poses health risks — has been studied repeatedly, and major regulatory bodies (FDA, EFSA, JECFA) have consistently concluded the dietary exposure is well below toxicity thresholds. People with phenylketonuria (PKU) need to avoid aspartame, but the warning is for the phenylalanine component, not the aspartate.
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.