Source Naturals L-Arginine and L-Citrulline are two amino acids bundled into a single powerful supplement. L-Arginine is an important factor in muscle. Citrulline (Cit) is a ubiquitous amino acid in mammals, is strongly related to it releases arginine and citrulline, amino acids that are important sources of. The body converts L-citrulline to L-arginine, another type of amino acid. L- arginine Watermelon is one of the best food sources of L-citrulline.