ornithine
Ornithine - An organic compound of the α-amino acid group, not belonging to the 20 basic α-amino acids building proteins but playing an important role in the ornithine cycle. It belongs to the basic amino acids. It occurs in living organisms, is involved in metabolism, is formed from arginine by enzymes. Ornithine in the ornithine cycle is transported from the cytosol to the mitochondria, in the presence of the enzyme ornithine carbamoyltransferase, attaches a carbamoylphosphate carbamoyl group to form citrulline, which is transported to the cytosol. Citrulline is combined with aspartic acid to form arginine succinate. The process requires energy from ATP. Arginine succinate is broken down by arginine succinate lyase into arginine, which is a precursor of urea. After leaving the urea cycle, arginine is transformed into ornithine and the cycle is repeated. As a result of decarboxylation, putrescine is produced from ornithine. Footnotes ...