From the Manufacturer:
Supports Muscle Metabolism. Works To Transport, Store, And Excrete Nitrogen. Source Naturals® L-Arginine is a crystalline, free-form amino acid. It is an important factor in muscle metabolism, and works to transport , store and excrete nitrogen. It is also a precursor of guanidophosphate, phosphoarginine, and creatine, three high-energy compounds found in muscles.