L-Arginine is a conditionally essential basic amino acid involved primarily in urea metabolism and excretion as well as DNA synthesis. Arginine also plays an important role in several important pathways, including the synthesis of proteins, the production of creatine phosphate, needed to produce ATP, and the synthesis of nitric oxide, a secondary messenger involved in blood flow.

Articles:

http://www.mayoclinic.com/health/l-arginine/NS_patient-arginine

http://en.wikipedia.org/wiki/Arginine