Arginase catalyzes the fifth and final step in the urea cycle, a series of biochemical reactions in mammals during which the body disposes of harmful ammonia. Specifically, arginase converts L-arginine into L-ornithine and urea.[2] Mammalian arginase is active as a trimer, but some bacterial arginases are hexameric.[3] The enzyme requires a two-molecule metal cluster of manganese in order to maintain proper function.