L-ornithine is one of the products of the action of the enzyme arginase on L-arginine, the creation of urea.
Therefore, ornithine is a central part of the urea cycle, which allows for the sale of excess nitrogen. Ornithine is recycled and in a way, a catalyst. First of all, ammonia is converted to carbamoyl phosphate (phosphate-CONH 2), which takes care of the one half of urea. Ornithine is converted into a urea derivative to the δ (terminal) of nitrogen by carbamoyl phosphate. Another nitrogen is added from aspartate, that the denitrogenated fumarate, and the resulting arginine (a guanidinium compound) is hydrolyzed back to ornithine, urea production.
The nitro-gens of urea are obtained from the ammonia and aspartate, and the nitrogen in ornithine remains intact.
Ornithine is not an amino acid encoded in DNA, and in that sense, is not involved in protein synthesis. However, in mammals, non-hepatic tissues, the main use of the urea cycle is arginine biosynthesis, therefore, as an intermediate in metabolic processes, ornithine is very important.