Arginase

Arginase (ARG) is an enzyme involved in urea cycle, where it catalyzes the hydrolysis of L-arginine into L-ornithine and urea. There are two distinct isoforms of arginase, arginase I and II, which are encoded by separate genes and display differences in tissue distribution, subcellular localization, and molecular regulation. Arginase activity has two major homeostatic purposes: first, to rid the body of ammonia through urea synthesis, and second, to produce ornithine, the precursor for polyamines and prolines. Polyamines produced through ornithine decarboxylase (ODC) are necessary for cell proliferation and regulation of several ion channels. Proline produced through ornithine aminotransferase (OAT) is necessary for production of collagen.

Arginase I is a cytosolic enzyme that is abundantly expressed in the liver and plays an essential role in hepatic urea cycle. In contrast, arginase II is a mitochondrial enzyme that is widely expressed outside the liver, most prominently in the kidney and prostate. Arginase functions important for protection against NH3 toxicity and cell growth and repair. Excessive arginase activity in mammals has been associated with cardiovascular and nervous system dysfunction and disease. Two relevant aspects of this elevated activity may be involved in these disease states. First, excessive arginase activity reduces the supply of L-arginine needed by nitric oxide (NO) synthase to produce NO. Second, excessive production of ornithine leads to vascular structural problems and neural toxicity. In addition, Arginase is a potential therapeutic target for the treatment of sexual arousal disorders in men and women.