Aspartic acid, also known as L-aspartate, is thought to help promote a robust metabolism, and is sometimes used to treat fatigue and depression. Aspartic acid plays an important role in the citric acid cycle, or Krebs cycle, during which other amino acids and biochemicals, such as asparagine, arginine, lysine, methionine, threonine, and isoleucine, are synthesized.
As its name indicates, aspartic acid is the carboxylic acid analog of asparagine. It is non-essential in mammals, and might serve as an excitatory neurotransmitter in the brain. Note that aspartic acid has an a-keto homolog, oxaloacetate, just as pyruvate is the a-keto homolog of alanine.