Products
Some preparations containing amino acids are approved as medicinal products. These include, for example, methionine tablets or infusion preparations for parenteral nutrition. Amino acids are also marketed as dietary supplements, such as lysine, arginine, glutamine, and cysteine tablets. Protein powders such as whey protein can also be counted as amino acid supplements. Amino acids are found in protein-rich foods. These include meat, fish, eggs, milk, hard cheeses, legumes, grains, soybeans, potatoes and nuts.
Structure and properties
Amino acids are organic compounds bearing a carboxy group and a primary amino group (secondary in the case of proline). The functional groups are differently protonated or deprotonated depending on pH. They are zwitterions. Of particular importance for human biology are the α-amino acids, which carry the amino group and the side chain (R) on the carbon atom in the α-position relative to the carboxy group. This C atom is chiral – with the exception of glycine. For humans, amino acids with the L-configuration are of primary importance. D-amino acids are rarer and occur, for example, in microorganisms. The L-α-amino acids differ in their side chain, which can be classified according to various criteria. They are referred to as branched, polar, apolar, acidic, basic, aliphatic, aromatic, cyclic, heterocyclic, sulfuric, and neutral amino acids. All chemical structures can be found later in the text. The simplest amino acid is glycine, which carries only one hydrogen atom as a “side chain” and is therefore non-chiral. Another simple amino acid is alanine with the methyl group as a side chain. The nine essential amino acids are not formed by the body itself and must be taken in with food. These include histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. Animal sources of protein contain all essential amino acids. Plant sources are incomplete but can be combined. The essential amino acids also include the branched-chain amino acids, the so-called BCAA (Branched-Chain Amino Acids): isoleucine, leucine and valine. Among other things, they are important for building up and supplying energy to the muscles and are therefore taken by bodybuilders. Amino acids can form two peptide bonds with two other amino acids. Linear chains (amides) are formed, which are called oligopeptides with few amino acids, peptides and proteins, depending on the length. The sequence is stored in the genetic code.
Important representatives
The 20 canonical and proteinogenic amino acids include:
| Alanine | Ala | A | Glucose metabolism |
| Arginine | Arg | R | Muscle formation, precursor of NO |
| Asparagine | Asn | N | Brain structure |
| Aspartic acid | Asp | D | Purine and pyrimidine synthesis. |
| Cysteine | Cys | C | Component of glutathione, for hair and nails |
| Glutamine | Gln | Q | Precursor of glutamate, important for intestinal mucosa |
| Glutamic acid | Glu | E | Neurotransmitter |
| Glycine | Gly | G | Neurotransmitter |
| Histidine | His | H | Precursor of histamine |
| Isoleucine | Ile | I | BCAA, muscle building |
| Leucine | Leu | L | BCAA, muscle building |
| Lysine | Lys | K | Prevention of cold sores |
| Methionine | Met | M | Prevention of cystitis |
| Phenylalanine | Phe | F | Precursor of catecholamines |
| Proline | Pro | P | Component of collagen (e.g., skin, hair) |
| Serine | Ser | S | Catalytic role in enzymes |
| Threonine | Thr | T | Precursor of glycine |
| Tryptophan | Trp | W | Precursor of serotonin and melatonin |
| Tyrosine | Tyr | Y | Precursor of hormones |
| Valine | Val | V | BCAA, muscle building |
In addition, there are numerous other amino acids such as β-alanine, ornithine, citrulline, carnitine, selenocysteine (also proteinogenic), GABA or sarcosine. By the way, taurine is not one of the amino acids, as it is an aminosulfonic acid.
Structures of amino acids
Effects
Proteinogenic L-amino acids are the building blocks from which proteins and peptides are constructed. Proteins have numerous functions in the organism and are found in every cell of the body. Among other things, they are found in muscle, skin, connective tissue and bone. Receptors, enzymes, transport proteins, antibodies, clotting factors and many hormones are all part of the protein family. In addition, amino acids have multiple metabolic effects that are important for health, growth, development, reproduction, and homeostasis. For example, amino acids are used for the synthesis of biologically active substances. Thyroid hormones and adrenaline are formed from tyrosine, serotonin and melatonin from tryptophan, histamine from histidine, and GABA from glutamate. Amino acids can also be used in the body to produce energy.
Areas of application
Amino acids are administered, among other things, for parenteral nutrition, convalescence, loss of appetite, hair loss, as tonics, and for muscle building. Defined areas of application exist for individual representatives (selection):
- Methionine for the prevention of cystitis.
- Lysine for the prevention of cold sores
- Tryptophan for depression and sleep disorders
- Glutamic acid for the promotion of mental performance
- Cysteine for the promotion of hair growth
- Glutamine in the context of “intestinal cleansing”.
- BCAA for muscle building
- Arginine for cardiovascular disease and to promote fertility.
In addition, there are numerous other uses. These usually follow the principle that a substitution (an increased selective supply) to achieve an enhanced effect.
Dosage
Nutritionists recommend a daily intake of 0.8 g of protein per kilogram of body weight for adults. Thus, for a body weight of 70 kg, the daily requirement is 56 g. The requirement is increased for pregnant and breastfeeding women.
Adverse effects
Gastrointestinal symptoms such as diarrhea, nausea, flatulence, and abdominal pain may occur when high doses are taken.
