Dicarboxylic Amino Acids

Dicarboxylic amino acids is a broad concept; there are very many of them. Primarily, they are glutamic and aspartic acids, whose share in the overall mass of dicarboxylic acids is very large. This section will discuss these specifically. Their conversion products (which are also amino acids) are glutamine and asparagine.

Glutamic and aspartic acids are becoming increasingly popular. They are available as drugs, dietary supplements, and are part of complex sports nutrition compositions, and are even produced as flavour enhancers (salts of glutamic acid). What do these amino acids represent? Let’s examine their role in the body.

There is a concept of „integration of nitrogen metabolism in the body“. Each food product contains a different set of amino acids. At certain times, the body may lack certain amino acids, and then they are synthesized from others.

All amino acids are divided into two main groups: dispensable and indispensable. Dispensable amino acids are those that are capable of mutual transformation (i.e. the body synthesizes them from each other): arginine, cystine, tyrosine, histidine, alanine, serine, proline, glycine, aspartic and glutamic acids. Indispensable amino acids are those that are not capable of mutual transformation: valine, isoleucine, leucine, lysine, methionine, threonine, tryptophan, phenylalanine.

The uniqueness of glutamic and aspartic amino acids lies in the fact that for mutual conversion into each other, all dispensable amino acids must first be converted into glutamic or aspartic acid. That is why they are said to play an integrating role in nitrogen metabolism. However, this role is not limited to compensating for the amino acids not obtained from food – there is also the phenomenon of „redistribution of nitrogen in the body“. In case of protein deficiency in an organ due to illness or hyperfunction (the need for working hypertrophy), there is a redistribution of nitrogen: protein is „extracted“ from some internal organs and directed to others. The most common source of easily mobilized protein are the transport proteins of the blood. When their reserve is exhausted, the proteins of the spleen, liver, kidneys, and intestines are used. The proteins of the heart and brain are never „spent“, as they are the most important organs of the body.

With heavy physical exertion and simultaneous dietary protein restriction, the protein of the internal organs is used to build muscle tissue of the skeletal muscles and the heart. High-level athletes may develop liver and kidney diseases due to the phenomenon of nitrogen redistribution. Hence, it becomes clear how necessary it is to receive a sufficiently large amount of protein from food.

In the redistribution of nitrogen in the body, all dispensable amino acids are first converted to glutamic and aspartic, and then to the amino acids that are lacking in the working organ.

Functions of Glutamic and Aspartic Acids

Glutamic acid is converted into glutamine by adding a molecule of ammonia. Ammonia is a highly toxic compound that is formed as a by-product of nitrogen metabolism and accounts for 80% of all nitrogen toxins. By adding ammonia, glutamic acid is converted into non-toxic glutamine, which in turn is incorporated into amino acid metabolism. Both glutamic acid and glutamine are used in complex sports nutrition formulations and dietary supplements. Which one is preferable? The answer to this question is unambiguous. Considering the detoxifying effect of glutamic acid, preference should be given to it. If the body needs glutamine for some purpose, it can easily obtain it by combining glutamic acid with ammonia (since the latter is always present in excess).

The biosynthesis of glutamic acid from carbohydrates (and primarily from glucose) is an extremely important backup mechanism for supplying the brain with glucose in the absence of carbohydrate nutrition or with very heavy physical exertion.

Glucose is the main energy supplier for the brain and spinal cord. It is absorbed by a non-insulin-dependent pathway, i.e. without the involvement of insulin. Without glucose, the brain dies very quickly, so the body has evolved reliable mechanisms for its endogenous synthesis. In case of glucose deficiency in the blood, the synthesis from amino acids, fats, lactic and pyruvic acids, ketoacids, alcohols, etc. is immediately activated. The process of glucose synthesis in the body is called gluconeogenesis, i.e. „new formation“ of glucose. Gluconeogenesis is most active in the liver; then the kidneys join this process and finally the intestines.

Glutamic acid is particularly actively converted into glucose in the intestines. In this process, it not only is able to transform itself, but also activates the synthesis of glucose (gluconeogenesis) from other substances in the liver and kidneys. Stimulation of gluconeogenesis leads to the utilization of lactic acid in the liver to form glucose. For this ability, glutamic acid is called a gluconeogenic amino acid. In its ability to stimulate (directly or indirectly) gluconeogenesis, it is inferior only to alanine.

The main pathway of glucose synthesis is the use of amino acids, and here the role of glutamic acid is very high.

A single dose of a large amount of glutamic acid after a workout can significantly reduce fatigue – due to more complete utilization of lactic acid, neutralization of ammonia, the energy-producing function of glutamic acid, and many other reasons.

Glutamic acid is involved in the biosynthesis of purine and pyrimidine nucleotides, which in turn are involved in the construction of DNA and RNA molecules. Purine and pyrimidine nucleotides have a distinct anabolic effect, especially on rapidly dividing cells, so they primarily improve hematopoiesis (blood-forming cells divide very quickly). Their anabolic effect on the gastrointestinal tract is slightly weaker, and even weaker on the skeletal musculature. But even if it were completely absent, purine and pyrimidine nucleotides would still have a positive effect on muscle growth – at least by improving the digestive capacity of the gastrointestinal tract.

Other Functions

Folic acid (vitamin Bc) is nothing other than pteroylglutamic acid and is naturally synthesized from glutamine. Folic acid does not act in isolation, by itself – it manifests its vitamin activity only in combination with vitamin B12 (cyanocobalamin). The main function of folic acid is an anabolic effect: it significantly improves protein metabolism by activating the activity of amino acids, purine and pyrimidine bases, as well as choline. Without folic acid, cell multiplication is impossible. Together with vitamin B12, it is present in chromosomes and regulates their division.

p-Aminobenzoic acid, or paraaminobenzoic acid (PABA for short), is another vitamin that is synthesized from glutamine. At first, it was thought that this acid was merely a precursor to the synthesis of folic acid, but later it turned out that this was not the case. PABA has great independent significance for the body: it is necessary for the normal pigmentation of hair, skin, and the iris of the eye, etc. In this case, pigmentation depends on a special kind of pigment – melanin. In recent years, it has been found that melanin not only contributes to pigmentation, but also performs adaptive and trophic functions. The highest content of melanin is in the brain. Melanin influences the strength and mobility of nervous processes. Some authors believe that it can be a source of the synthesis of catecholamines – neurotransmitters of an excitatory type of action. In the light of these studies, the appearance of gray hair can be interpreted as the result of age-related depletion of the catecholamine depot. Their synthesis consumes all the available reserves of melanin, and for the hair there is not enough of it left.

Glutamic acid is one of the few compounds that, along with glucose, can serve as the main source of energy for the brain.