Carbamoyl phosphate synthetase I

Definition

Carbamoyl phosphate synthetase I (CPS I) is an essential enzyme in the urea cycle that catalyzes the formation of carbamoyl phosphate from ammonia and bicarbonate, using ATP as a phosphate donor. This reaction occurs in the mitochondria of liver cells and is a crucial step in the detoxification of ammonia, ultimately leading to the production of urea for excretion. The activity of CPS I is tightly regulated by the availability of its substrates and allosteric effectors, making it a key player in nitrogen metabolism.

5 Must Know Facts For Your Next Test

1. CPS I is located in the mitochondrial matrix, where it initiates the urea cycle by converting ammonia and bicarbonate into carbamoyl phosphate.
2. The reaction catalyzed by CPS I is irreversible and is considered the committed step of the urea cycle, making it crucial for regulating nitrogen elimination.
3. CPS I requires ATP to function, and its activity increases in response to high levels of ammonia in the blood, which signals the need for more urea production.
4. N-acetylglutamate acts as an important regulator of CPS I, enhancing its activity when amino acid breakdown leads to elevated ammonia levels.
5. Deficiencies in CPS I can lead to hyperammonemia, a condition characterized by elevated ammonia levels in the blood that can cause severe neurological problems.

Review Questions

• How does carbamoyl phosphate synthetase I contribute to the detoxification of ammonia?
  • CPS I plays a critical role in detoxifying ammonia by catalyzing the conversion of ammonia and bicarbonate into carbamoyl phosphate. This reaction is the first step in the urea cycle, which processes excess nitrogen from amino acid metabolism. By facilitating this conversion, CPS I helps prevent the accumulation of toxic ammonia in the bloodstream, allowing it to be safely converted into urea for excretion.
• Discuss the regulation of carbamoyl phosphate synthetase I and its importance in maintaining nitrogen balance.
  • CPS I is regulated through allosteric activation by N-acetylglutamate, which signals increased amino acid breakdown and elevated ammonia levels. The enzyme's activity adjusts according to the metabolic needs of the body, ensuring that excess nitrogen is efficiently processed into urea. This regulation is crucial for maintaining nitrogen balance and preventing hyperammonemia, which can lead to serious health issues.
• Evaluate the consequences of a deficiency in carbamoyl phosphate synthetase I on human health and metabolism.
  • A deficiency in CPS I leads to hyperammonemia due to impaired conversion of ammonia to urea. This condition can cause severe neurological effects, including confusion, lethargy, and even coma if untreated. The inability to efficiently process nitrogen results in metabolic imbalances and highlights the importance of CPS I in maintaining overall health. Understanding these consequences underscores the need for effective management strategies for individuals with this enzyme deficiency.

Related terms

Urea Cycle: A series of biochemical reactions in the liver that convert ammonia, a toxic byproduct of protein metabolism, into urea for excretion.

Ammonia: A nitrogenous waste product generated from amino acid metabolism, which is highly toxic and must be converted into less harmful substances like urea.

N-acetylglutamate: An allosteric activator of CPS I, formed from glutamate and acetyl-CoA, that enhances the enzyme's activity in response to increased levels of ammonia.