Arginine Totally Explained

Everything about Arginine totally explained

Arginine (abbreviated as Arg or R) is an α-amino acid. The L-form is one of the 20 most common natural amino acids. Its codons are CGU, CGC, CGA, CGG, AGA, and AGG. In mammals, arginine is classified as a semiessential or conditionally essential amino acid, depending on the developmental stage and health status of the individual. Infants are unable to meet their requirements and thus arginine is nutritionally essential for infants. Arginine was first isolated from a lupin seedling extract in 1886 by the Swiss chemist Ernst Schulze.

Structure

Arginine consists of a 4-carbon aliphatic straight chain, the distal end of which is capped by a complex guanidinium group. With a pK_a of 12.48, the guanidinium group is positively charged in neutral, acidic and even most basic environments, and thus imparts basic chemical properties to arginine. Because of the conjugation between the double bond and the nitrogen lone pairs, the positive charge is de-localized, enabling the formation of multiple H-bonds.

Sources

Dietary Sources

Arginine is a nonessential amino acid, meaning it can be manufactured by the human body, and doesn't need to be obtained directly through the diet. The biosynthetic pathway however doesn't produce sufficient arginine, and some must still be consumed through diet. Arginine is found in a wide variety of foods, including:

Animal sources: dairy products (for example cottage cheese, ricotta, milk, yogurt, whey protein drinks), beef, pork (for example bacon, ham), poultry (for example chicken and turkey light meat), wild game (for example pheasant, quail), seafood (for example halibut, lobster, salmon, shrimp, snails, tuna in water)
Vegetarian sources: wheat germ and flour, buckwheat, granola, oatmeal, nuts (coconut, pecans, cashews, walnuts, almonds, Brazil nuts, hazel nuts, pine nuts, peanuts), seeds (pumpkin, sesame, sunflower), chick peas, cooked soybeans, chocolate
Other: some energy drinks and body building supplements

Biosynthesis

Arginine is synthesized from citrulline by the sequential action of the cytosolic enzymes argininosuccinate synthetase (ASS) and argininosuccinate lyase (ASL). This is energetically costly, as the synthesis of each molecule of argininosuccinate requires hydrolysis of adenosine triphosphate (ATP) to adenosine monophosphate (AMP); for example, two ATP equivalents.
Citrulline can be derived from multiple sources:

from arginine via nitric oxide synthase (NOS);

from ornithine via catabolism of proline or glutamine/glutamate;

from asymmetric dimethylarginine (ADMA) via DDAH. The pathways linking arginine, glutamine, and proline are bidirectional. Thus, the net utilization or production of these amino acids is highly dependent on cell type and developmental stage.
On a whole-body basis, synthesis of arginine occurs principally via the intestinal–renal axis, wherein epithelial cells of the small intestine, which produce citrulline primarily from glutamine and glutamate, collaborate with the proximal tubule cells of the kidney, which extract citrulline from the circulation and convert it to arginine, which is returned to the circulation. Consequently, impairment of small bowel or renal function can reduce endogenous arginine synthesis, thereby increasing the dietary requirement.
Synthesis of arginine from citrulline also occurs at a low level in many other cells, and cellular capacity for arginine synthesis can be markedly increased under circumstances that also induce iNOS. Thus, citrulline, a coproduct of the NOS-catalyzed reaction, can be recycled to arginine in a pathway known as the citrulline-NO or arginine-citrulline pathway. This is demonstrated by the fact that in many cell types, citrulline can substitute for arginine to some degree in supporting NO synthesis. However, recycling isn't quantitative because citrulline accumulates along with nitrate and nitrite, the stable end-products of NO, in NO-producing cells.

Function

Arginine plays an important role in cell division, the healing of wounds, removing ammonia from the body, immune function, and the release of hormones. Arginine, taken in combination with proanthocyanidins or yohimbine, has also been used as a treatment for erectile dysfunction. Unlike synthetically created L-Arginine.
The benefits and functions attributed to oral ingestion of L-arginine include:
• Precursor for the synthesis of Nitric Oxide (NO)
• Stimulation of the release of the most important anti-aging hormone in the body, growth hormone.
• Improves immune function
• Reduces healing time of injuries (particularly bone)
• Reduces risk of heart disease
• Increases muscle mass
• Reduces adipose tissue body fat
• Helps improve insulin sensitivity
• Helps decrease blood pressure
• Alleviates male infertility, improving sperm production and motility

In proteins

The geometry, charge distribution and ability to form multiple H-bonds make arginine ideal for binding negatively charged groups. For this reason arginine prefers to be on the outside of the proteins where it can interact with the polar environment. Incorporated in proteins, arginine can also be converted to citrulline by PAD enzymes. In addition, arginine can be methylated by protein methyltransferases.

As a precursor

Arginine is the immediate precursor of NO, 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. For being a precursor of NO, (relaxes blood vessels), arginine is used in many conditions where vasodilation is required. 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.

Treatment of Herpes simplex virus

A low ratio of arginine to lysine may be of benefit in the treatment of Herpes simplex. For more information, refer to Herpes simplex - Treatment.

Possible Increases in risk of death from heart disease

A clinical trial found that patients taking an L-arginine supplement following a heart attack didn't improve in their vascular tone or their hearts' ability to pump. In fact, more patients died who were taking L-arginine than placebo and the study was stopped early with the recommendation the supplement not be used by heart attack patients. The supplement still is widely marketed.

Growth hormone

Arginine increases the production of growth hormone. Reports of its effects on male muscular development are not clearly proven.

Prolactin

Although there haven't been thorough studies, some sources claim that arginine helps release prolactin, an estrogenic compound which is associated with lactation, and like all estrogenic compounds may curb the secretion of testosterone. Thus some bodybuilders stay away from pure arginine, intaking only amounts naturally found in protein.

Further Information

Get more info on 'Arginine'.

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