Aspartic acid is a non-essential amino acid that is adequately supplied in the diet. It is a component of most proteins. Along with glutamate, aspartic acid functions as a neurotransmitter.
What is aspartic acid?
Aspartic acid represents a nonessential amino acid that is sufficiently present in all protein-containing foods. It contains two acid groups, making it an acidic amino acid. Its biosynthesis takes place in the body very simply from oxalic acid by transamination. It occurs in two optically active forms, with D-aspartic acid having no biological significance. Only the L-aspartic acid is a proteinogenic amino acid. When aspartic acid is mentioned, the L-form is always meant in the following. In biochemistry, it is often also referred to as L-aspartate because it is usually present in the body deprotonated. In the urea cycle, aspartate serves as an amino group donor. Aspartic acid is also produced industrially by the addition of ammonia to the double bond of fumaric acid. It is of great importance as a starting material for the production of the sweetener aspartame. Aspartame is a dipeptide of the amino acids aspartic acid and phenylalanine. It is also used for parenteral nutrition in infusion solutions or as a salt former. Its technical use as a polyaspartic acid ester in modern paint systems is also interesting.
Function, action, and tasks
The most important function of aspartic acid is its participation in protein assembly. It is one of the 20 proteinogenic amino acids. Along with glutamate, L-aspartate functions as a neurotransmitter in over half of all synapses in the vertebrate central nervous system. The exact mode of action of aspartic acid has not yet been researched in detail. Among other things, it is thought to be active in the climbing fibers of the cerebellum and in the mossy fibers of the ammonium horn formation. Overall, however, it is said to exert a weaker effect than glutamate. Aspartic acid acts by stimulating NMDA receptors. It is also a precursor for the formation of nucleic bases. In this process, it is available for the synthesis of pyrimidine bases. In the urea cycle, aspartic acid is converted to argininosuccinate with the help of the enzyme argininosuccinate synthetase. Argininosuccinate is a metabolite of the urea cycle. It is a non-proteinogenic amino acid which is degraded by the enzyme argininosuccinate lyase into the proteinogenic amino acid arginine and fumarate. As part of the urea cycle, L-arginine releases ammonia. The ammonia released by L-arginine is converted to urea, which is excreted by the kidneys. Fumarate converts back to oxaloacetate (oxalic acid). The oxalic acid is transaminated again to aspartic acid with the help of an alpha amino acid. Glutamic acid is usually available for this purpose, which is then converted to ketoglutarate.
Formation, occurrence, properties, and optimal values
Aspartic acid is widely distributed. It is difficult to imagine malnutrition leading to a deficiency of aspartic acid. L-aspartate is present in all protein-containing foods. Particularly high concentrations are found in vegetable asparagus. Asparagus, with its Latin name Asparagus officinalis, is the eponym for the amino acids asparagine and aspartic acid. Very high levels of L-aspartate are also found in legume sprouts, soy protein, dried egg white, cod, peanut flour, dried spirulina, tofu and also sunflower seed flour. However, dietary intake is not necessary. Aspartic acid is one of the amino acids that can also be synthesized in sufficient quantities in the metabolism. Even if L-aspartate were not supplied in the diet, a deficiency would not occur because it is one of the amino acids with the simplest structure and easy to synthesize.
Diseases and disorders
The main health effect of aspartic acid is to convert ammonia to urea via the urea cycle and to channel it out of the body. The additional intake of L-aspartate is thought to help improve ammonia detoxification. In this regard, studies have reportedly found aspartate to have positive effects on fatigue, fatigue, and low exercise tolerance. However, the research results are not so clear that the effect can be conclusively assessed.However, evidence has been found that a low concentration of aspartic acid in the organism is associated with stressful situations and states of exhaustion. Together with lysine, aspartic acid can also be used for heavy metal elimination by forming complexes with heavy metals. There are contradictory statements about possible negative side effects when taking too high doses of l-aspartate. According to some sources, there are no side effects, while other reports talk about bad nerve damage. Effects on nerve function are suspected because aspartic acid acts as a neurotransmitter along with glutamate. However, no clear statements have been made on this so far. The sweetener aspartame has caused much discussion. Aspartame is a dipeptide of phenylalanine and aspartic acid. Studies have been conducted that have produced controversial results. Thus, after the consumption of sweetened food and beverages with aspartame, isolated cases of migraine, other headaches, mood disorders, depressive moods and many more have been described. However, a connection with the sweetener could not be proven and in some cases even excluded. However, there is a clear contraindication of aspartame for people with phenylketonuria. In phenylketonuria, the amino acid phenylalanine leads to severe metabolic disorders. In this disease, a special low-phenylalanine diet must also be followed in other ways. The incidence of this disease is approximately 1 in 8000, which is why aspartame is labeled as containing phenylalanine. However, this contraindication has nothing to do with the aspartic acid contained in aspartame. Overall, it can be said that quite contradictory statements are available for aspartic acid with regard to health effects, which do not allow a conclusive assessment.
