Ornitina

Ornitina, known in English as ornithine, is a non‑proteinogenic α‑amino acid that plays a central role in the urea cycle, a metabolic pathway responsible for converting toxic ammonia into urea for excretion. Chemically, it is a diamino acid with the formula C5H12N2O2; its side chain contains a secondary amine, distinguishing it from the proteinogenic amino acids.

In mammals, ornitina is synthesized primarily from arginine via the enzyme arginase, which releases urea and yields ornithine. The regenerated ornithine then combines with carbamoyl phosphate, forming citrulline in the first step of the urea cycle, which continues through a series of enzymatic reactions to ultimately produce urea. This cycle occurs mainly in liver mitochondria and is essential for nitrogen homeostasis.

Beyond the urea cycle, ornitina serves as a precursor for polyamine biosynthesis. Through decarboxylation by ornithine decarboxylase, it generates putrescine, which can be further converted into spermidine and spermine, compounds important for cell growth, differentiation, and stabilization of nucleic acids. Dysregulation of ornithine metabolism is implicated in certain metabolic disorders, such as hyperornithinemia‑hyperammonemia‑homocitrullinuria (HHH) syndrome, often linked to deficiencies in the mitochondrial transporter responsible for ornithine uptake.

Dietary sources of ornithine include protein‑rich foods such as meat, fish, dairy, and legumes, although the body can also synthesize sufficient amounts endogenously. Supplementation is sometimes explored for its potential to support liver function and wound healing, but scientific evidence remains limited.