Alanine is a nonessential proteinogenic amino acid that serves as a building block for the synthesis of proteins. It is a chiral compound, and only the L form can be incorporated into proteins. In this context, alanine acts as a link between amino acid and carbohydrate metabolism.
What is alanine?
Alanine represents a proteinogenic amino acid. It can be synthesized by the human organism and is therefore nonessential. The amino acid referred to as alanine is actually called alpha-L-alanine. In this name, the position of the amino group with respect to the carboxyl group becomes clear. In addition, only the L-form of alanine is used for protein synthesis. The D form is used by bacteria to synthesize murein, which forms the cell membrane of bacteria. Another amino acid in this context is beta-alanine. Here the amino group is located at the beta carbon atom. Beta-alanine is not a proteinogenic amino acid. However, it also plays a major role in biological processes. However, when alanine is referred to here, it is always alpha-L-alanine. Alanine has a positive center at the nitrogen atom and a negative center at an oxygen atom of the carboxyl group. Thus, alanine represents a zwitterion. At the isoelectric point of alanine at a pH of 6.1, almost all molecules exist as zwitterions. Therefore, under these conditions, its water solubility is lowest. However, alanine is a hydrophilic amino acid and this property also helps determine the secondary and tertiary structure of proteins.
Function, action, and roles
The most important function of alanine is to participate as a basic building block in protein assembly. The structure of alanine makes it preferentially occur in the alpha helix of the protein. Together with the amino acids glutamic acid or leucine, alanine thus determines the formation of the helix and thus also the secondary structure of the protein. In metabolism, alanine is synthesized from pyruvate by transamination. Pyruvate is an intermediate product of metabolism. It is formed during the breakdown of sugars, fatty acids or amino acids. Either it is further degraded or it serves again as a starting material for further syntheses. The degradation of alanine functions as a reverse reaction to the transamination of pyruvate. With the aid of the enzyme alanine dehydrogenase, alanine is deaminated back to pyruvate. Since pyruvate can also be rapidly converted back to glucose, the close link between amino acid metabolism and carbohydrate metabolism becomes clear. In the event of a sudden demand for energy, hypoglycemia can occur for a short time. This causes the release of stress hormones, which stimulate the deamination of alanine and the conversion of pyruvate to glucose in the liver. This process keeps the blood glucose level constant. Because of this fact, alanine supplements are often given in the event of hypoglycemia to prevent sugar shock. Alanine also has a strengthening effect on the immune system. Furthermore, it also inhibits the formation of kidney stones. Alanine is an important component of muscle proteins. Muscle fibers contain up to 6 percent alanine. It is released again when the muscles are broken down. The alanine contained in the blood comes to 30 percent from the muscles. The main metabolic organ is the liver. It is in the liver that most of the conversion reactions of alanine take place. Via liver metabolism, the amino acid has a regulating effect on insulin production. Furthermore, decongestant effects on the prostate have been noted.
Formation, occurrence, properties, and optimal values
Particularly high concentrations of alanine are found in meat and fish products. Mushrooms, sunflower seeds, soy flour, wheat germ or even parsley also have a high alanine content. Normally, the amount of alanine produced in the body and the amount supplied through food are completely sufficient. Due to its water solubility, alanine is washed out of food when it comes into contact with water for a long time. For this reason, alanine-rich products should never be soaked or cooked for long periods of time. Deficiency states occur only rarely. However, in competitive sports there is an increased need for alanine, so that an additional application via protein-rich food or protein powder can be useful. In any case, alanine has a positive effect on training success. It is contained in high concentrations in both muscle fibers and connective tissue.
Diseases and disorders
What health effects an alanine deficiency has on the body has hardly been studied.Such a deficiency state can normally only occur in cases of extreme malnutrition. In this case, however, there is no longer an isolated alanine deficiency. Alanine is generally sufficiently available to the body both from food and from the body’s own biosynthesis. Alanine synthesis takes place in the liver. The same applies to the breakdown of alanine. The enzyme alanine aminotransferase is available in the liver for this purpose. Alanine aminotransferase is a transaminase and is known by the abbreviation GPT. GPT catalyzes the conversion of L-alanine with alpha-ketoglutarate. In this process, the amino group is transferred to alpha-ketoglutarate to form L-glutamate. Alanine is converted to pyruvate in the process. These reactions take place within the liver cells. Transaminase is therefore present in the blood only in low concentrations. An increase in the enzyme concentration in the blood indicates destruction of the liver cells. Besides GPT (alanine aminotransferase or newly glutamate pyruvate transaminase), other enzyme levels are also elevated. This is called elevation of liver enzymes. With the help of liver values it becomes possible to diagnose liver diseases. The first sign of liver disease may be an increase in liver enzymes. This applies to all forms of hepatitis, liver cirrhosis or even liver cancer. If liver disease continues to progress, the organ can no longer fulfill its many tasks for metabolism and detoxification.
