ureakierroksen

Ureakierroksen, also known as the "urea cycle" or "ornithine cycle," is a biochemical cycle that converts ammonia, a toxic byproduct of protein metabolism, into urea, which is much less toxic and can be excreted by the kidneys. This cycle primarily takes place in the liver and is crucial for maintaining ammonia levels within a safe range in the bloodstream.

The urea cycle involves a series of five enzymatic reactions that incorporate nitrogen, derived from ammonia and aspartate, into urea. The cycle starts with the synthesis of carbamoyl phosphate from ammonia and carbon dioxide, a reaction catalyzed by the enzyme carbamoyl phosphate synthetase I. This enzyme is activated by N-acetylglutamate, which is synthesized from acetate and glutamate.

The next step involves the combination of carbamoyl phosphate with ornithine to form citrulline, a reaction catalyzed by ornithine transcarbamylase. Citrulline is then combined with aspartate to form argininosuccinate, a reaction catalyzed by argininosuccinate synthetase. Argininosuccinate is then cleaved to form arginine and fumarate, a reaction catalyzed by argininosuccinate lyase. Finally, arginine is hydrolyzed to form urea and ornithine, a reaction catalyzed by arginase. Ornithine is then recycled back into the cycle, hence the name "urea cycle."

Disruptions in the urea cycle can lead to a group of genetic disorders known as urea cycle disorders, which can result in the accumulation of ammonia in the blood, a condition known as hyperammonemia. Symptoms of hyperammonemia can include vomiting, seizures, and coma, and if left untreated, can be fatal. Treatment for urea cycle disorders typically involves a combination of dietary modifications, medications, and in some cases, liver transplantation.