Arginine

Arginine (abbreviated as Arg or R) is one of the 20 amino acids found in proteins. In liver tissue, arginine can be synthesized in the ornithine cycle (or urea cycle). This amino acid or total amino acid is involved in many of the activities of the endocrine glands. Its side chain is formed by a guanidino group.

Chemistry

Arginine is a conditionally essential amino acid (needed in the diet only under certain conditions), and it can stimulate immune function by increasing the number of white blood cells. Arginine is involved in the synthesis of creatine, polyamines and in DNA. It has been shown that in vascular endothelial cells, L-arginine is the precursor of the synthesis of nitric oxide (NO). It can lower cholesterol to improve the capacity of the circulatory system, as well as stimulate the release of growth hormone (somatropin), reduce body fat levels and facilitate recovery in athletes due to the effects it has of removing ammonia (muscle residue resulting from anaerobic exercise) from the muscles and converting it into urea that is excreted in the urine. It is used in the biosynthesis of creatine. It is usually found in certain ergogenic products that contain nitric oxide (NO) as it enhances the vasodilatory effects.

Arginine is characterized by having a guanidinium group (H-N=(NHR)NH2), and therefore, when ionized, it has a lower charge density than other amino acids such as lysine, and higher than histidine.

Arginine is an amino acid that is included in cats' balanced diets; its absence can cause serious disorders related to excess ammonia in their tissues.

History

Arginine was isolated for the first time from lupine seed extract in 1886. Arginine is an amino acid that is used in ingredients of many cosmetic creams, with the false idea that its epidermal application would be capable of stimulating protein and transform it into muscle. Many studies have tried in various ways to extract arginine in its pure form or in oils, but this is difficult, since like vitamin C and many other substrates, it is destroyed by heat, between 39 and 50 °C.

Arginine is found in the vast majority of sea products, fish, shellfish, crustaceans, large aquatic mammals such as whales make an oil with them, this oil is demanded by various cosmetic companies for its arginine content.

Summary

Arginine is synthesized from citrulline by the sequential action of the cytosolic enzymes argininosuccinate synthetase (ASS) and argininosuccinate lyase (ASL). This is energetically expensive, since the synthesis of each argininosuccinate molecule requires the hydrolysis of adenosine triphosphate (ATP) to adenosine monophosphate (AMP); i.e., two ATP equivalents.

Citrulline can be supplied from multiple sources:

• arginine via synthesized nitric oxide (NOS);
• of the ornithine via catabolism of proline or glutamine/glutamate;
• of asymmetric dimethylarginine (ADMA) via DDAH.

The pathways of arginine, glutamine, and proline links are bidirectional. That is, the net utilization or production of these amino acids is highly dependent on the cell type and stage of development.

In the body, arginine synthesis occurs primarily via the intestinal–renal axis, where the epithelia of the small intestine, which produce citrulline primarily from glutamine and glutamate, collaborate with the proximal tubular cells of the kidney, which extract citrulline. circulation and converts it to arginine, which is placed in the circulation. Consequently, intestinal or renal function abnormalities may reduce endogenous arginine synthesis, making it necessary to increase the dietary requirement for the amino acid.

Arginine synthesis from citrulline occurs at a low level in many other tissues, and tissue capacity to synthesize arginine can be markedly increased under circumstances that also induce nitric oxide synthetase (iNOS). Thus, citrulline, a co-product of the NOS-catalyzed reaction, can be recycled to arginine in the biochemical citrulline-NO pathway or arginine-citrulline pathway. This is demonstrated by the type of tissues, citrulline can be substituted for arginine to various degrees to support NO synthesis. However, citrulline accumulates along with nitrates and nitrites, the final stable forms of NO, in NO-producing cells.