What does citrulline mean?
Citrulline is an amino acid that occupies an unusual place in biochemistry: unlike most amino acids, it is not incorporated into proteins by the human body's genetic code. Instead, it serves chiefly as an intermediate in the urea cycle, the liver's pathway for disposing of excess nitrogen, and it is readily converted into arginine, which in turn supports the production of nitric oxide — a molecule that helps relax and widen blood vessels. The name reflects its history: citrulline was first isolated from watermelon juice, whose botanical genus Citrullus derives from the Latin word for the fruit, and watermelon remains its richest natural food source. In contemporary usage the word appears mostly in scientific, medical, and fitness contexts, where L-citrulline and citrulline malate are marketed as supplements intended to improve blood flow, reduce muscle soreness, and enhance athletic endurance. Clinicians also track citrulline levels as a marker of intestinal function. Though technical in flavor, the term has entered mainstream vocabulary through the growing popularity of sports nutrition.
nounAn amino acid, not one of the standard twenty used to build proteins in humans, that participates in the urea cycle and is involved in the body's production of nitric oxide; it is named for the watermelon, its richest natural dietary source.
- The amino acid citrulline itself: a non-proteinogenic alpha-amino acid intermediate in the urea cycle, produced from ornithine and converted in the kidneys into arginine.
- A dietary supplement form (typically L-citrulline or citrulline malate) taken by athletes and others to support blood flow and exercise performance.
"Watermelon is one of the best dietary sources of citrulline."
"Because citrulline is converted into arginine in the kidneys, some studies suggest it raises arginine levels in the blood more effectively than taking arginine directly."
"Many pre-workout powders combine citrulline malate with caffeine to boost training performance."
Rarely pluralized; the plural would appear only in contexts comparing multiple forms or analogues of the compound.
"Several synthetic citrullines were tested for their stability in solution."
Citrulline got its name because it was first isolated from watermelon — a fruit so rich in it that eating watermelon can measurably raise levels of this blood-vessel-friendly amino acid.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of citrulline
Citrulline was first isolated in the early twentieth century, notably from the juice of watermelon, and was named after the fruit's botanical genus, Citrullus. The genus name traces back to Latin citrullus, a diminutive of citrus, referring to the gourd-like fruit. The word thus shares its root with English 'citrus' and 'citron'.
How citrulline is actually used
Citrulline is a technical term used mainly in biochemistry, medicine, sports nutrition, and health journalism. In everyday writing it appears almost exclusively as 'L-citrulline' (the naturally occurring stereoisomer) or 'citrulline malate' when discussing supplements. It carries no emotional connotation; register is neutral-to-formal.
Easily confused with citrulline
Arginine is a different, protein-building amino acid that the body converts to citrulline and vice versa; the two are chemically related but distinct compounds with separate roles.