H2O + L-arginine = L-ornithine + urea Binds 2 manganese ions per subunit. Nitrogen metabolism; urea cycle; L-ornithine and urea from L-arginine: step 1/1. Homotrimer. Strongest expression in liver. First expressed at stage 10/11 of gastrulation. Higher levels found at stages 23/24 and 60-62. In the intestine, expression increased during metamorphosis (stage 62/64) and then, decreased. In the tail region, highest levels were found at the time of tail resorption. Activated, but at low levels, at stages 56-58 of hindlimb development. Slow-response activation by thyroid hormone (T3). Belongs to the arginase family.