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ASS (argininosuccinate synthetase) is a human gene that provides instructions for making an enzyme called argininosuccinate synthetase. This enzyme participates in the urea cycle, which is a sequence of chemical reactions that takes place in the cells of the liver. The urea cycle processes excess nitrogen (which is generated as the body uses proteins) into a compound called urea that is excreted from the body in urine.
Argininosuccinate synthase is responsible for the third step of the urea cycle. This reaction combines two amino acids (building blocks of proteins), citrulline and aspartate, to form a molecule called argininosuccinic acid. A series of additional chemical reactions uses argininosuccinic acid to form urea.
The ASS gene is located on the long (q) arm of chromosome 9 at position 34.1, from base pair 130,349,861 to base pair 130,406,214.
Related conditions
Citrullinemia: At least 50 mutations that cause type I citrullinemia have been identified in the ASS gene. Most of these mutations substitute one amino acid for another amino acid in the argininosuccinate synthetase enzyme. These mutations likely affect the structure of the enzyme and its ability to bind to citrulline, aspartate, and other molecules. A few mutations lead to the production of an abnormally short enzyme that cannot effectively play its role in the urea cycle.
Defects in argininosuccinate synthase disrupt the third step of the urea cycle, preventing the liver from processing excess nitrogen into urea. As a result, nitrogen (in the form of ammonia) and other byproducts of the urea cycle (such as citrulline) build up in the bloodstream. Ammonia is toxic, particularly to the nervous system. An accumulation of ammonia during the first few days of life leads to poor feeding, vomiting, seizures, and the other signs and symptoms of type I citrullinemia.
See also
References
- PMID 12815590
- PMID 11941481
External links
"ASS (gene)"