Carbamoyl phosphate synthetase I

Definition

Carbamoyl phosphate synthetase I (CPS I) is an enzyme that catalyzes the first step in the urea cycle by converting ammonia and bicarbonate into carbamoyl phosphate, using ATP as a phosphate donor. This reaction is crucial for the detoxification of ammonia produced during amino acid degradation, linking amino acid metabolism to the urea cycle, which ultimately helps to eliminate excess nitrogen from the body.

5 Must Know Facts For Your Next Test

1. CPS I is located in the mitochondria of liver cells and is primarily responsible for initiating the urea cycle.
2. The enzyme requires N-acetylglutamate as an essential allosteric activator for optimal activity.
3. CPS I is regulated by the levels of ammonia; high ammonia concentrations increase its activity to facilitate more rapid urea formation.
4. Deficiencies in CPS I can lead to hyperammonemia, a dangerous condition characterized by elevated ammonia levels in the blood.
5. CPS I uses two molecules of ATP to convert one molecule of bicarbonate and one molecule of ammonia into one molecule of carbamoyl phosphate.

Review Questions

• How does carbamoyl phosphate synthetase I contribute to the urea cycle and why is it vital for nitrogen metabolism?
  • Carbamoyl phosphate synthetase I initiates the urea cycle by converting ammonia and bicarbonate into carbamoyl phosphate, which is then used in subsequent reactions to eventually form urea. This process is crucial because it helps detoxify ammonia, a potentially harmful byproduct of amino acid degradation. By efficiently converting excess nitrogen into urea for excretion, CPS I plays a key role in maintaining nitrogen balance and preventing toxic accumulation.
• Discuss the regulatory mechanisms that influence the activity of carbamoyl phosphate synthetase I and their physiological significance.
  • The activity of carbamoyl phosphate synthetase I is regulated primarily by N-acetylglutamate, which acts as an allosteric activator. This regulation is significant because it ensures that CPS I operates effectively when there is an increased need for urea synthesis, particularly during times of high protein intake or increased amino acid catabolism. Additionally, higher levels of ammonia can stimulate CPS I activity, providing a feedback mechanism that allows for rapid detoxification when ammonia concentrations rise.
• Evaluate the clinical implications of deficiencies in carbamoyl phosphate synthetase I and how such conditions might affect overall metabolism.
  • Deficiencies in carbamoyl phosphate synthetase I can lead to severe hyperammonemia, resulting in neurological impairments and potentially life-threatening conditions due to toxic ammonia buildup. The inability to effectively convert ammonia into urea disrupts normal nitrogen metabolism and can have cascading effects on amino acid levels and overall metabolic balance. Understanding these implications is critical for developing therapeutic strategies, such as dietary management or alternative therapies, to mitigate the effects of such enzymatic deficiencies on patient health.

Related terms

Urea Cycle: A series of biochemical reactions in the liver that convert ammonia into urea for excretion, playing a critical role in nitrogen metabolism.

Ammonia: A toxic byproduct of amino acid catabolism that must be converted into less harmful substances, like urea, for safe excretion from the body.

ATP: A high-energy molecule that provides energy for various biochemical reactions, including the phosphorylation process in carbamoyl phosphate synthesis.