Is Arginine in Proteins?

Proteins are complex molecules constructed from simpler, nitrogen-containing molecules called amino acids. Your body uses 20 amino acids to manufacture the entire range of proteins it needs. Ten of these -- what nutritionists call the "essential" amino acids -- must be obtained from your diet because your cells do not possess the synthetic machinery to produce them. Arginine, a "conditionally essential" amino acid, is found in many proteins, but it has nonprotein functions as well.

Conditionally Essential

Arginine is usually synthesized in your cells from citrulline, another amino acid. However, the November 2002 issue of "Biomedicine and Pharmacotherapy" reports that arginine is a "conditionally essential" amino acid in some people. Infants and young children, who require additional amino acids to support growth and development, cannot manufacture enough arginine to meet their metabolic demands. Even some adults -- pregnant women or trauma victims, for example -- might require extra dietary arginine, as their cells cannot synthesize enough to meet their additional needs.

Protein Functions

According to Dr. Elson Haas, author of "Staying Healthy with Nutrition," proteins serve more functions than any other nutritional component in your body, and arginine is in dozens of proteins. For example, albumin, the most abundant protein in your bloodstream, contains arginine, which is also found in hemoglobin, the oxygen-carrying protein in your red blood cells; pepsin, a digestive enzyme produced by your stomach; and insulin, a pancreatic hormone that drives glucose metabolism in your cells. Many food proteins -- casein, whey, egg whites and tuna, for example -- contain arginine.

Nonprotein Functions

Like many amino acids, arginine serves various roles beyond its participation in building proteins. Nitric oxide, an important signaling molecule in your body, is produced from arginine, a critical component of a metabolic pathway called the urea cycle, which enables your body to rid itself of toxic ammonia. Arginine has a beneficial effect on your immune system, and it encourages the release of growth hormone, a property that is sometimes exploited by bodybuilders.

Considerations

Although healthy adults can usually synthesize enough arginine for their daily needs, growing children, pregnant women and individuals under stress -- trauma, surgery, illness or extreme exertion -- might need additional arginine from their diet or supplemental sources; 3 to 4 grams of arginine daily are needed to increase your growth hormone levels, but these doses can trigger nausea and diarrhea in some people. Ask your doctor if you need additional arginine.