Ornithine Cycle Explained

The ornithine cycle is a fascinating process that involves the conversion of arginine to ornithine. The process involves the reactions of Argininosuccinate and Ornithine transcarbamoylase. Despite its complex nature, there are many factors that can affect the cycle. In this article, we will look at the role of each enzyme in the process.


The Ornithine cycle helps the body eliminate toxic ammonia, arginine, and citrulline. During the process, carbon dioxide is produced and enters the cytosol. The synthesis of ornithine requires the presence of the enzyme, ornithine transcarbamoylase. The enzyme is activated by glutamate and n-acetylglutamate.

Ornithine is synthesized in the liver using amino acids. The excess amino acids are transported to liver cells through the portal vein (hepatic portal vein). Once there, the liver removes the amino group from the amino acid. The resulting product is organic acid, which is useful for the body’s cells. However, it also produces a toxic substance known as ammonia. Then, the process repeats itself.

During the first step of citrulline synthesis, the enzyme ornithine transcarbamoylase reacts with aspartate. Aspartate is the source of the second amine group on urea. In the second step, argininosuccinate is cleaved into arginine. Afterwards, arginine undergoes hydrolysis by arginase, which converts it into urea and ornithine.


The Ornithine cycle is a metabolic pathway that helps the liver detoxify nitrogenous waste. It is a very energy-intensive process, consuming nearly a third of the hepatic energy budget. Each turn of the Ornithine cycle uses about three ATPs, and ligation of citrulline to aspartate requires argininosuccinate synthetase. The enzyme argininosuccinate synthetase catalyzes the conversion of one ATP to AMP. This process may be essential for maintaining nitrogen balance.

Argininosuccinate synthase is a protein in the liver that catalyzes the condensation of citrulline with aspartate to produce arginine and NO. It was initially discovered as a limiting enzyme in the urea cycle, but is now recognized as a ubiquitous enzyme in mammalian cells. It is thought that the regulation of this protein varies between cells and tissues, and its regulation may affect the synthesis of other a-keto acids.


The Ornithine cycle is a complex chemical process in the human body. Arginine and H2O are used to produce urea. Arginase is an enzyme that converts arginine into urea. This enzyme is essential for a healthy body. In the human body, this enzyme is present in most cells. The following is a description of its function.

Arginine is a building block of urea. Arginine is converted into urea through a series of reactions. The urea is then converted back into ornithine. This process is important for the body’s ability to eliminate waste products. But how does the Arginase enzyme work? Here are the details:

Arginase and NOS compete for the same substrate, l-arginine. NOS also oxidizes arginine into citrulline. Arginase and NOS are expressed in tissues, and their coexpression raises interesting questions about how arginine flux is regulated. It is important to note that there is little direct evidence to support a link between the two enzymes, but this may not be the case.

Ornithine transcarbamoylase

Ornithine transcarbamolylase (OTCase) is a liver-specific enzyme involved in the conversion of l-ornithine to citrulline. Its activity is increased during acute liver failure. This enzyme is also involved in polyamine metabolism. The enzyme is present in the mitochondria of hepatocytes.

Deficiency of ornithine transcarbamylase causes elevated levels of ammonia in the blood. Ammonia is a natural waste product of protein breakdown, and the body needs to eliminate this waste product through the urine. If the amount of ammonia is too high in the body, it can affect the nervous system and liver. In cases of OTC deficiency, symptoms may range from vomiting and lethargy to coma.

The urea cycle is carried out in the liver. There are six enzymes in the urea cycle. Arginase, carbmyl phosphate synthase and ornithine transcarbamylase are intramitochondrial enzymes. The other three enzymes are cytosolic, ornithine transcarbamylase and arginase.

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