The first amino acid ever discovered — isolated from asparagus juice in 1806, decades before anyone knew what an amino acid was.
Symbol
Asn · N
Discovered
1806
Mol. Weight
132.12 g/mol
Essential
No
N
Discovery: The First of Twenty
L-Asparagine
The story of amino acid chemistry begins in Paris, in 1806, with a simple experiment: two chemists, Louis-Nicolas Vauquelin and Pierre Jean Robiquet, took asparagus juice and slowly evaporated it. As the liquid concentrated, white crystals formed and settled. The crystals were something new — a compound nobody had isolated before.
They named it asparagine, after asparagus. It was a reasonable choice: they had no idea that they had just opened a 130-year chapter of chemistry. The concept of "amino acids" didn't exist yet. The molecular structure of asparagine wouldn't be understood for decades. All Vauquelin and Robiquet knew was that they had crystallized something interesting from a vegetable.
🌿 Paris, 1806: Asparagus and a New Kind of Chemistry
Louis-Nicolas Vauquelin was already one of France's most celebrated chemists — he had discovered the elements chromium and beryllium. His collaborator Pierre Jean Robiquet would go on to independently discover caffeine (1821) and isolate codeine (1832). But in 1806, their most historically significant contribution was a pile of white crystals from a pot of concentrated asparagus juice.
What they had found was the first amino acid — the first of the 20 standard building blocks of all proteins on Earth. They didn't know that yet. But every amino acid discovery that followed over the next 130 years would trace its intellectual lineage back to that single experiment.
Chemical and Physical Properties of Asparagine
Identity
IUPAC Name(2S)-2,4-Diamino-4-oxobutanoic acid
FormulaC₄H₈N₂O₃
Mol. Weight132.12 g/mol
CAS Number70-47-3
MDL NumberMFCD00064401
Physical
Melting point235 °C
Solubility20 g/L (20 °C)
pKa₁ (COOH)2.02
pKa₂ (NH₃⁺)8.80
pI5.41
Rf (BuOH/AcOH/H₂O = 12:3:5)0.50
Identifiers
Canonical SMILESC(C(C(=O)O)N)C(=O)N
Isomeric SMILESC([C@@H](C(=O)O)N)C(=O)N
InChIKeyDCXYFEDJOCDNAF-REOHCLBHSA-N
CategoryPolar
EssentialNo
The Amide Group: Chemistry's Subtle Modifier
Asparagine is structurally very similar to aspartic acid — with one key difference. Where aspartic acid has a carboxyl group (–COOH) at the end of its side chain, asparagine has an amide group (–CONH₂). This single substitution changes everything about the molecule's behavior: aspartic acid is acidic and carries a negative charge at cellular pH; asparagine is neutral and polar but uncharged.
That amide group also makes asparagine one of the most important attachment points for sugars in glycoproteins. When the cell wants to decorate a protein with carbohydrate chains — for signaling, structural support, or cell surface recognition — it often does so by linking sugars to the nitrogen atom of asparagine. This process, called N-linked glycosylation, is one of the most common protein modifications in all of biology.
Functions of L-Asparagine in the Body
Asparagine is a non-essential amino acid, synthesized by the body primarily in the liver. It participates in several important biological processes.
Glycoprotein biosynthesis
One of asparagine's most critical roles is as the attachment site for N-linked glycosylation — the process by which carbohydrate chains are added to proteins. The cell recognizes a specific sequence (Asn-X-Ser/Thr) as the signal for this modification. Many essential proteins, including antibodies, cell surface receptors, and clotting factors, depend on this modification for their correct folding, stability, and function.
Nitrogen transport
Asparagine is one of the principal amino acids used to transport nitrogen between tissues. Its amide group carries an extra nitrogen atom, making it an efficient vehicle for moving nitrogen in a non-toxic form through the bloodstream — particularly from sites of protein breakdown to sites of protein synthesis.
Nervous system function
Asparagine is involved in the synthesis of proteins required for neuronal development and synaptic transmission. Adequate asparagine availability is important for the normal functioning of the nervous system, where it contributes to the pool of amino acids needed to build and maintain signaling proteins.
Liver function
The liver both synthesizes and processes asparagine as part of normal amino acid metabolism. Asparagine participates in transamination reactions in the liver and supports the broader metabolic processes involved in urea synthesis and nitrogen balance.
Did You Know?
The asparagine in potatoes reacts with sugars at high temperatures to form acrylamide — explaining why golden-brown fried potatoes contain a compound that was once thought to be purely industrial.
Asparagine and Acrylamide
In 2002, Swedish researchers discovered something unexpected in fried and baked starchy foods: significant amounts of acrylamide, a compound that had long been considered an industrial chemical with no place in food. The source turned out to be asparagine.
Chemistry in the Kitchen
🍟 Why Fried Potatoes Contain Acrylamide
When foods rich in asparagine (potatoes, cereals, bread) are heated above about 120°C in the presence of reducing sugars, the asparagine undergoes a reaction pathway that produces acrylamide. The same Maillard browning reaction that creates the delicious golden crust on fried potatoes also generates this byproduct. It's not a contamination — it's chemistry inherent to cooking starchy, asparagine-rich foods at high temperatures.
Interesting Facts
🥇
The very first. Asparagine is the oldest known amino acid, isolated 14 years before glycine (1820) and 129 years before the last standard amino acid, threonine (1935). Every amino acid ever named was discovered in the wake of Vauquelin and Robiquet's asparagus experiment.
🔗
The sugar attachment site. N-linked glycosylation — attaching carbohydrate chains to proteins — almost always happens on asparagine residues. The cell uses a specific sequence (Asn-X-Ser/Thr, where X is any amino acid except proline) as the recognition signal. Many critical proteins, including antibodies and cell surface receptors, are decorated with sugars at asparagine sites.
🎯
Targeted in cancer treatment. Some leukemia cells cannot synthesize asparagine and depend entirely on asparagine from the bloodstream. The drug asparaginase exploits this by breaking down blood asparagine — starving the cancer cells while leaving normal cells (which can synthesize their own) relatively unaffected. It's one of the most elegant examples of metabolic targeting in oncology.
💧
Why asparagus makes urine smell. Asparagine itself isn't responsible for the notorious post-asparagus urinary odor — it's the breakdown products, particularly methanethiol and dimethyl sulfide, that form when asparagine and other compounds in asparagus are metabolized. Interestingly, not everyone can detect the smell: the ability to notice it is genetically determined.
Where Asparagine Is Found
True to its name, asparagine is particularly concentrated in asparagus. It is also found across a wide range of plant and animal proteins. Since the body synthesizes asparagine on its own, there is no specific dietary requirement — a varied, balanced diet provides adequate amounts for most people.
