HOOCCHNH2CH2COOH

HOOCCHNH2CH2COOH corresponds to aspartic acid, an α-amino acid characterized by two carboxyl groups and a four-carbon backbone. The molecule carries an amino group on the α-carbon and carboxyl groups on both the α-carboxyl and the side-chain carboxyl, giving it acidic properties. In solution it exists mainly as a zwitterion, with the amino group as NH3+ and both carboxyls as COO− at physiological pH. The biologically common enantiomer is L-aspartic acid; the D-enantiomer occurs in some organisms.

Aspartic acid participates broadly in metabolism and biosynthesis. It is synthesized in humans and many organisms from oxaloacetate via transamination, using an amino donor such as glutamate. It can be converted to asparagine by asparagine synthetase, and it serves as the nitrogen donor in the urea cycle when it combines with citrulline to form argininosuccinate. Through its interconversion with oxaloacetate, aspartate links amino acid metabolism with the citric acid cycle and other pathways, contributing to nucleotide and amino acid biosynthesis.

Biological roles and properties: aspartic acid is one of the standard amino acids incorporated into proteins during translation. It also functions as a neurotransmitter (aspartate) in some contexts and participates in various metabolic processes, including energy metabolism, nucleotide synthesis, and the regulation of enzyme activities. Its two carboxyl groups confer high polarity and multiple ionization states, making it highly soluble in water and negatively charged at physiological pH.

Chemical identity and notation: molecular formula C4H7NO4; molar mass about 133.10 g/mol; IUPAC name 2-aminobutanedioic acid. In life, it occurs widely in dietary proteins and is available as a free amino acid and in derivative forms; it is generally regarded as non-essential for humans, since it can be synthesized endogenously.