Aspartate, also known as aspartic acid, is one of the 20 standard amino acids that serve as the fundamental building blocks for proteins in the human body. It is an alpha-amino acid with a specific chemical structure. Aspartate is classified as a non-essential amino acid, meaning the human body can produce it internally and does not strictly require it from dietary sources. In biological discussions, “aspartate” and “aspartic acid” are often used interchangeably. This amino acid plays a role in various biological processes, extending beyond its direct incorporation into proteins.
Biochemical Functions
Beyond its role as a building block for proteins, aspartate participates in several cellular processes. It is involved in the synthesis of new proteins, where it is incorporated into growing polypeptide chains. Aspartate makes up around 7% of the amino acid content found in human proteins.
Aspartate also plays a role in the urea cycle, a metabolic pathway that helps the body eliminate excess nitrogen, a byproduct of amino acid breakdown. In this cycle, aspartate donates one of the two nitrogen atoms incorporated into urea, which is then excreted. This process helps sustain the cycle’s flow of nitrogen and prevents harmful ammonia buildup.
Aspartate also participates in the malate-aspartate shuttle, a system that facilitates cellular energy production. This shuttle transports energy packages, in the form of NADH, from the cytosol into the mitochondria, the cell’s energy-generating compartments. Since the inner mitochondrial membrane is not permeable to NADH, the shuttle uses malate to carry these equivalents across the membrane. Aspartate is transported out of the mitochondria in exchange for glutamate, supporting the efficient generation of ATP.
Role as a Neurotransmitter
Aspartate functions as an excitatory neurotransmitter within the brain and nervous system. Excitatory neurotransmitters stimulate nerve cells, increasing the likelihood that they will generate an electrical signal, known as an action potential. Aspartate primarily interacts with specific receptors on nerve cells, particularly the N-methyl-D-aspartate (NMDA) receptor. Along with glutamate, aspartate is considered one of the primary excitatory amino acid neurotransmitters.
The NMDA receptor is a type of ligand-gated ion channel that plays a role in neuronal communication and synaptic plasticity. Under resting conditions, a magnesium ion blocks this receptor’s channel, preventing ion flow. When the nerve cell membrane depolarizes, this magnesium block is dislodged, allowing calcium ions to enter the cell upon activation by aspartate or glutamate.
This calcium influx is important for synaptic plasticity, a cellular mechanism that underpins learning and memory formation. Strong and sustained activation of NMDA receptors contributes to long-term potentiation, which strengthens connections between neurons and is considered the basis for lasting memories. Proper NMDA receptor function is therefore linked to cognitive abilities.
While its stimulatory role is necessary for normal brain function, excessive activation by excitatory neurotransmitters, including aspartate, can become harmful. This overstimulation is known as excitotoxicity, where prolonged calcium passage into nerve cells can lead to cellular damage or death. This process is implicated in various neurological disorders, showing that maintaining a balanced level of aspartate activity is important for overall brain health.
Dietary Sources and Synthesis
The primary pathway for aspartate production occurs through transamination, where an amino group is transferred to another molecule. This process involves the transfer of an amino group from glutamate to oxaloacetate, a key intermediate in the body’s central energy-generating pathway, the citric acid cycle. This reaction yields aspartate.
Beyond the body’s internal production, aspartate is naturally present in a variety of foods. As a constituent of many proteins, it is widely distributed across protein-rich dietary sources.
- Animal-based sources include meat (beef, poultry, fish), eggs, and dairy products (milk, cheese).
- Plant-based sources include legumes, soy products, whole grains, and nuts.
- Specific vegetables like asparagus, avocados, and potatoes also contain aspartic acid.
Aspartic acid or its salts, like magnesium aspartate, can also be found in some dietary supplements.
Aspartate and Aspartame
It is important to clarify that aspartate and aspartame are distinct substances, despite their similar names. Aspartame is a synthetic artificial sweetener, widely used as a sugar substitute in various foods and beverages to reduce calorie content. It is approximately 200 times sweeter than sucrose, or table sugar, meaning only a very small amount is needed to achieve desired sweetness. Common brand names for aspartame include NutraSweet and Equal.
Aspartame is chemically a methyl ester of a dipeptide, meaning it is formed by chemically linking two specific amino acids: aspartic acid and phenylalanine. It also contains a small amount of methanol. When aspartame is consumed and digested in the small intestine, it is rapidly broken down by digestive enzymes into its constituent parts: aspartic acid, phenylalanine, and methanol.
These breakdown products are then absorbed by the body, similar to how these compounds are absorbed from other food sources. Importantly, the amount of aspartic acid, phenylalanine, and methanol derived from typical aspartame consumption is less than or comparable to amounts found naturally in many common foods and drinks, such as fruit juices and vegetables. Due to its rapid and complete metabolism, no intact aspartame is found in the bloodstream after ingestion.