ornithine metabolic process

Definition

Target type: biologicalprocess

The chemical reactions and pathways involving ornithine, an amino acid only rarely found in proteins, but which is important in living organisms as an intermediate in the reactions of the urea cycle and in arginine biosynthesis. [GOC:jl, ISBN:0192801023]

Ornithine metabolism is a critical process in the biosynthesis of urea, the primary means by which mammals excrete excess nitrogen. It also plays a role in the synthesis of polyamines, essential for cell growth and differentiation. The process begins with the conversion of L-arginine to ornithine and urea by the enzyme arginase. Ornithine then enters the urea cycle, where it serves as a carrier of ammonia to the mitochondria. Inside the mitochondria, ornithine reacts with carbamoyl phosphate, a molecule containing ammonia and carbon dioxide, to form citrulline. Citrulline exits the mitochondria and enters the cytosol, where it combines with aspartate to form argininosuccinate. Argininosuccinate is then cleaved to form arginine and fumarate. The arginine produced can be used to generate more urea or can be utilized in other metabolic pathways, such as the biosynthesis of polyamines. Ornithine can also be synthesized from glutamate via the enzyme glutamate-5-semialdehyde dehydrogenase. This pathway is particularly important in tissues that do not express arginase, such as the brain. Disruptions in ornithine metabolism can lead to various genetic disorders, including citrullinemia, argininemia, and hyperornithinemia-hyperammonemia-homocitrullinemia syndrome (HHH syndrome). These conditions are characterized by elevated levels of ornithine and/or other urea cycle intermediates in the blood and urine, leading to neurological dysfunction and potentially life-threatening hyperammonemia.'
"

Proteins (1)

Compounds (3)