NOW Supplements L-Citrulline 750mg Capsules, 90 Count Citrulline is a non-essential amino acid that is an important intermediate in the urea cycle, functioning along with other amino acids to rid the body of ammonia, a by-product of protein metabolism. NOW Supplements L-Arginine 500mg Capsules, 100 Count L-Arginine is a conditionally essential basic amino acid involved primarily in urea metabolism and excretion, as well as in DNA synthesis and protein production. It is an important precursor of nitric oxide (no) and thus plays a role in the dilation of blood vessels. NPN 80002671.Product 2: Helps the detoxification of ammonia in the body. Product 2: Supports protein and creatine synthesis, nitric oxide production. Product 2: It is an important precursor of Nitric Oxide (NO) and thus plays a role in the dilation of blood vessels. Product 2: L-Arginine is a conditionally essential basic amino acid involved primarily in urea metabolism and excretion, as well as in DNA synthesis and protein production. Product 1: Our NOW natural and organic Supplements are an effective way to ensure you and your loved ones are getting essential vitamins, minerals and nutrients for daily optimal health. Product 1: L-Citrulline vegan capsule supports protein metabolism and healthy immune system function. Product 1: Citrulline also plays an important role in the healing process and in the maintenance of a healthy immune system. Product 1: This non-essential amino acid is an important intermediate in the urea cycle, functioning along with other amino acids to rid the body of ammonia, a byproduct of protein metabolism.