[6][7] Apart from a few rare exceptions, D-aspartic acid is not used for protein synthesis but is incorporated into some peptides and plays a role as a neurotransmitter/neuromodulator.

[5] Under physiological conditions (pH 7.4) in proteins the side chain usually occurs as the negatively charged aspartate form, −COO−.

[9] Aspartic acid was first discovered in 1827 by Auguste-Arthur Plisson and Étienne-Ossian Henry[10][11] by hydrolysis of asparagine, which had been isolated from asparagus juice in 1806.

[15] In plants and microorganisms, aspartate is the precursor to several amino acids, including four that are essential for humans: methionine, threonine, isoleucine, and lysine.

It carries reducing equivalents in the malate-aspartate shuttle, which utilizes the ready interconversion of aspartate and oxaloacetate, which is the oxidized (dehydrogenated) derivative of malic acid.

Current applications include biodegradable polymers (polyaspartic acid), low calorie sweeteners (aspartame), scale and corrosion inhibitors, and resins.

[citation needed] One area of aspartic acid market growth is biodegradable superabsorbent polymers (SAP), and hydrogels.

[22] Around 75% of superabsorbent polymers are used in disposable diapers and an additional 20% is used for adult incontinence and feminine hygiene products.

[22][23][24] In addition to SAP, aspartic acid has applications in the fertilizer industry, where polyaspartate improves water retention and nitrogen uptake.