Aspartate

Aspartate is the deprotonated form of the amino acid aspartic acid and, in biology, refers to the L- and D- enantiomers. In proteins, the L-enantiomer is the form incorporated into polypeptides. At physiological pH, the molecule carries a negative charge due to its side-chain carboxylate, making it an acidic amino acid.

Chemically, aspartate has two carboxylate groups: the alpha-carboxyl and a side-chain carboxylate. This arrangement yields a negatively charged molecule under normal cellular conditions. Aspartate participates in numerous metabolic processes and can be interconverted with oxaloacetate through transamination, linking amino acid and carbohydrate metabolism and contributing to the malate-aspartate shuttle that transfers reducing equivalents across mitochondrial membranes.

Biologically, aspartate serves several roles. It donates an amino group in the urea cycle, forming argininosuccinate with citrulline. It is also a nitrogen donor for the synthesis of nucleotides (both purines and pyrimidines). Additionally, aspartate residues are one of the standard amino acids in proteins, and in humans small amounts of D-aspartate are found in certain tissues with specialized roles.

Occurrence and clinical relevance: aspartate is present in many dietary proteins. The enzyme aspartate aminotransferase (AST) is commonly measured in liver function tests; elevated AST activity can indicate tissue damage or disease. Aspartate is a precursor for various biomolecules and, in some contexts, derivatives such as aspartame (a sweetener) are used commercially.