Aspartate

What is aspartate?

Aspartate is the ionized form of the amino acid aspartic acid, which is used to build proteins and support metabolism. The body can make it, which is what “nonessential” means in this context.

Aspartate vs. aspartic acid

The names refer to closely related chemical forms. More precisely, L-aspartate(1−) is the conjugate base of L-aspartic acid: it has lost a hydrogen ion and carries a net negative charge.

Metabolism: nitrogen and energy

Nitrogen transfer and the urea cycle

Amino-group transfer moves nitrogen between molecules. One example is the formation of aspartate when an amino group from glutamate is transferred to oxaloacetate. In the liver’s urea cycle, aspartate then supplies one of the two nitrogen atoms in urea. The cycle packages waste nitrogen into urea for removal in urine.

The malate–aspartate shuttle

The malate–aspartate shuttle solves a different problem. NADH, an electron carrier produced outside mitochondria during glucose breakdown, cannot simply cross the inner mitochondrial membrane. A linked series of reactions and exchanges involving malate and aspartate transfers its reducing power to NADH inside. The electrons can then enter the respiratory chain, supporting ATP production. The shuttle transfers reducing power across the membrane, rather than transporting the original NADH molecule through it.

Aspartate function in the brain

Alongside its metabolic roles, aspartate can activate NMDA receptors. Its role as a neurotransmitter, however, is less well established than glutamate’s.

Rae, Rowlands, and Balcar’s review explains the distinction. Activating a receptor is only one part of the evidence needed; evidence about vesicular storage and release in response to stimulation remains incomplete.

Connection to Canavan disease

Canavan disease involves a related compound, N-acetylaspartate, and a deficiency of the enzyme aspartoacylase that breaks it down. The disease damages the brain’s white matter, including the myelin that insulates nerve fibers.

Aspartate, N-acetylaspartate, and the enzymes involved have distinct roles.