Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. The enzyme ornithine decarboxylase (ODC) participates in the urea cycle, and in the metabolism of glutathione and amino groups. In humans, this protein has 461 amino acids and forms a homodimer. The urea cycle (also known as the ornithine cycle) is a cycle of biochemical reactions occurring in many animals that produces urea (NH2)2CO from ammonia (NH3). This cycle was the first metabolic cycle discovered (Hans Krebs and Kurt Henseleit, 1932). In mammals, the urea cycle takes place primarily in the liver, and to a lesser extent in the kidney.