Biochem/physiol Actions

Arginosuccinic acid is a basic amino acid, which is synthesized by some cells from citrulline, aspartic acid and used as a precursor for arginine in the urea cycle or Citrulline-NO cycle. The reaction is catalyzed by the enzyme argininosuccinate synthetase. Argininosuccinic acid is a precursor to fumarate in the citric acid cycle via argininosuccinate lyase. Defects in the arginosuccinate lyase enzyme can lead to arginosuccinate lyase deficiency. Argininosuccinate (ASA) lyase deficiency results in defective cleavage of ASA. This leads to an accumulation of ASA in cells and an excessive excretion of ASA in urine (arginosuccinic aciduria). In virtually all respects, this disorder shares the characteristics of other urea cycle defects. The most important characteristic of ASA lyase deficiency is its propensity to cause hyperammonemia in affected individuals. ASA in affected individuals is excreted by the kidney at a rate practically equivalent to the glomerular filtration rate (GFR). Whether ASA itself causes a degree of toxicity due to hepatocellular accumulation is unknown; such an effect could help explain hyperammonemia development in affected individuals. Regardless, the name of the disease is derived from the rapid clearance of ASA in urine, although elevated levels of ASA can be found in plasma. ASA lyase deficiency is associated with high mortality and morbidity rates.