THEME AND FOCUS: AMINO ACIDS Case Study: A female neonate did well until approximately 24 hours of age when she became lethargic. A sepsis workup proved negative. At 54 hours, she staed showing focal seizure activity. The plasma ammonia level was found to be 1,000 mmol/L (normal 5-35 mmol/L). Quantitative plasma amino acid levels revealed a marked elevation of argininosuccinate. Lead Question: Which one of the following enzymic activities is most likely to be deficient in this patient?
Genetic deficiencies of each of the five enzymes of the urea cycle, as well as deficiencies in N-acetyglutamate synthase, can lead to increase in plasma ammonia levels. The accumulation of argininosuccinate in the plasma of this patient means that the enzymes required for its synthesis are functional But the enzyme required for its cleavage (argininosuccinate lyase or argininosuccinase) to arginine plus fumarate is not
Arginase.
Argininosuccinate lyase.
Argininosuccinate synthase.
Carbamoyl phosphate synthetase I.
Urea cycle