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Citrullinemia type I (CTLN1), also known as arginosuccinate synthetase deficiency, is a rare disease caused by a deficiency in argininosuccinate synthetase, an enzyme involved in excreting excess nitrogen from the body. [1] There are mild and severe forms of the disease, which is one of the urea cycle disorders.
Argininosuccinate synthetase is a homotetramer, with each subunit consisting of 412 residues. [6] The interfaces between subunits contain a number of salt bridges and hydrogen bonds, and the C-terminus of each subunit is involved in oligomerization by interacting with the C-termini and nucleotide-binding domains of the other subunits.
The enzyme made by this gene, argininosuccinate synthetase (EC 6.3.4.5), is responsible for one step of the urea cycle. Mutations in the ASS gene reduce the activity of the enzyme, which disrupts the urea cycle and prevents the body from processing nitrogen effectively. Excess nitrogen, in the form of ammonia, and other byproducts of the urea ...
Argininosuccinate synthetase is an enzyme that in humans is encoded by the ASS1 gene. [ 5 ] [ 6 ] [ 7 ] The protein encoded by this gene catalyzes the penultimate step of the arginine biosynthetic pathway .
Argininosuccinate lyase is an intermediate enzyme in the urea synthesis pathway and its function is imperative to the continuation of the cycle. A non-functioning enzyme results in patients' accumulation of ammonia, argininosuccinate, and citrulline in the blood, and argininosuccinate is excreted in the urine. [ 9 ]
Argininosuccinic aciduria is an inherited disorder that causes the accumulation of argininosuccinic acid (also known as "ASA") in the blood and urine. Some patients may also have an elevation of ammonia, a toxic chemical, which can affect the nervous system.
The enzyme that catalyzes the reaction is argininosuccinate synthetase. [ 3 ] [ 4 ] Argininosuccinic acid is a precursor to fumarate in the citric acid cycle via argininosuccinate lyase .
Due to accumulation of argininosuccinate, citrulline, and arginine in the liver when the urea cycle is deficient. Hyperammonemia , or high ammonia levels , is a metabolic disturbance characterised by an excess of ammonia in the blood .