Arginine (non-essential amino acid).
Arginine is a nonessential amino acid that is used in the biosynthesis of proteins. It is physiologically active in the L-form and is one of the 20 genetically encoded amino acids.
Arginine is referred to as nonessential because it can be synthesized by the body. It is synthesized from citrulline in arginine and proline metabolism by the sequential action of the cytosolic enzymes argininosuccinate synthetase (ASS) and argininosuccinate lyase (ASL). This is an energetically costly process, because for each molecule of argininosuccinate that is synthesized, one molecule of adenosine triphosphate (ATP) is hydrolyzed to adenosine monophosphate (AMP), consuming two ATP equivalents.
Although nonessential in humans, arginine is classified as a semi essential or conditionally essential amino acid, depending on the developmental stage and health status of the individual. Preterm infants are unable to synthesize or create arginine internally, making the amino acid nutritionally essential for them. Most healthy people do not need to supplement with arginine because it is a component of all protein-containing foods and can be synthesized in the body from glutamine via citrulline.
Important in the regulation of blood pressure.
Involved in the synthesis of creatine.
Arginine plays an important role in cell division, wound healing, removing ammonia from the body, immune function, and the release of hormones. It is a precursor for the synthesis of nitric oxide (NO), making it important in the regulation of blood pressure.
Arginine's side chain is amphipathic, because at physiological pH it contains a positively charged guanidinium group, which is highly polar, at the end of a hydrophobic aliphatic hydrocarbon chain. Because globular proteins have hydrophobic interiors and hydrophilic surfaces, arginine is typically found on the outside of the protein, where the hydrophilic head group can interact with the polar environment, for example taking part in hydrogen bonding and salt bridges. For this reason, it is frequently found at the interface between two proteins. The aliphatic part of the side chain sometimes remains below the surface of the protein.
Arginine residues in proteins can be deiminated by PAD enzymes to form citrulline, in a post-translational modification process called citrullination.This is important in fetal development, is part of the normal immune process, as well as the control of gene expression, but is also significant in autoimmune diseases. Another post-translational modification of arginine involves methylation by protein methyltransferases.
Arginine is the immediate precursor of nitric oxide (NO), an important signaling molecule which can act as a second messenger as well as an intercellular messenger which regulates vasodilation, and also has functions in the immune system's reaction to infection.
Arginine is also a precursor for urea, ornithine, and agmatine; is necessary for the synthesis of creatine; and can also be used for the synthesis of polyamines (mainly through ornithine and to a lesser degree through agmatine), citrulline, and glutamate. The presence of asymmetric dimethylarginine (ADMA), a close relative, inhibits the nitric oxide reaction; therefore, ADMA is considered a marker for vascular disease, just as L-arginine is considered a sign of a healthy endothelium.
Sources: meat, diary, eggs, and plant seeds.
Arginine is a conditionally essential amino acid in humans, as it may be required depending on the health status or life cycle of the individual. For example, while healthy adults can supply their own requirement for arginine, immature and rapidly growing individuals require arginine in their diet, and it is also essential under physiological stress, for example during recovery from burns, injury and sepsis, or when the small intestine and kidneys, which are the major sites of arginine biosynthesis have been damaged.
Animal sources of arginine include meat, dairy products and eggs, and plant sources include seeds of all types, for example grains, beans, and nuts.
Deficiency can cause hair loss and impende wound healing.
Deficiency can cause a buildup of ammonia in the blood.
Although arginine is a nonessential amino acid, it is semi essential in certain conditions like starvation, following low protein diets etc. Deficiency can also be caused by decreased rate of endogenous arginine synthesis.
The amino acid arginine plays a variety of roles in many different cell types. In addition to serving as substrate for protein synthesis, arginine is a precursor to nitric oxide (NO), polyamines, proline, glutamate, creatine, and agmatine. Consequently, deficiencies of arginine have the potential to disrupt many cellular and organ functions.
L-Arginine is a precursor of nitric oxide (NO) in the human body. In the 1990s, scientists discovered that not only is NO an essential compound that helps blood circulation, but it is important to normal sexual function in both men and women. A deficiency would therefore impair sexual functioning in both men and women.
Arginine deficiency can also cause problems with the skin such as rash and hair loss due to its reported ability to increase blood supply to the skin. More serious conditions such as poor wound healing may also result, particularly important for those with burns and infections.
Arginine is also involved in the removal of ammonia in the body. Deficiency can cause a buildup of ammonia in the blood. Ammonia is toxic if levels become too high; the nervous system is especially sensitive to the effects of excess ammonia.
Excess can cause abdominal cramps and diarrhea.
Oral supplementation with L-arginine at doses up to 15 grams daily are generally well tolerated. The most common adverse reactions of higher doses from 15 to 30 grams daily are nausea, abdominal cramps and diarrhea. Some may experience these symptoms at lower doses.
L-arginine is generally recognized as safe (GRAS-status) at intakes of up to 20 grams per day.