Citrulline: A non-standard amino acid that is not normally present in protein. Citrulline is created in the body as an intermediate in the conversion of the amino acid ornithine to arginine in a metabolic pathway called the urea cycle.
Citrulline was first isolated from watermelon. The term citrulline was coined in 1930 from citrullus, the Latin name of the watermelon.
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