Carbamoyl Phosphate Synthetase I

Definition

Carbamoyl phosphate synthetase I (CPS I) is a mitochondrial enzyme that catalyzes the first committed and rate-limiting step in the urea cycle, which is the primary pathway for the disposal of excess nitrogen in the body. This enzyme plays a crucial role in protein metabolism by converting ammonia and bicarbonate into carbamoyl phosphate, an essential precursor for the synthesis of urea.

5 Must Know Facts For Your Next Test

1. CPS I is located in the mitochondria of liver cells and is the first and rate-limiting enzyme in the urea cycle.
2. The enzyme catalyzes the condensation of ammonia and bicarbonate to form carbamoyl phosphate, which is then used in subsequent steps of the urea cycle.
3. Deficiency or dysfunction of CPS I can lead to a build-up of ammonia in the body, a condition known as hyperammonemia, which can be life-threatening if not properly managed.
4. The activity of CPS I is regulated by various factors, including the availability of substrates (ammonia and bicarbonate), allosteric modifiers, and hormonal signals.
5. CPS I is essential for maintaining nitrogen balance and preventing the accumulation of toxic ammonia in the body, which is particularly important for individuals with certain inborn errors of metabolism or liver disease.

Review Questions

• Explain the role of carbamoyl phosphate synthetase I (CPS I) in the urea cycle and protein metabolism.
  • Carbamoyl phosphate synthetase I (CPS I) is the first and rate-limiting enzyme in the urea cycle, which is the primary pathway for the disposal of excess nitrogen in the body. CPS I catalyzes the condensation of ammonia and bicarbonate to form carbamoyl phosphate, an essential precursor for the synthesis of urea. This process is crucial for protein metabolism, as it allows the body to convert toxic ammonia, a byproduct of protein breakdown, into a less toxic compound that can be safely excreted. By facilitating the removal of excess nitrogen, CPS I plays a key role in maintaining nitrogen balance and preventing the accumulation of ammonia, which can be life-threatening if not properly managed.
• Describe the potential consequences of a deficiency or dysfunction of carbamoyl phosphate synthetase I (CPS I).
  • A deficiency or dysfunction of carbamoyl phosphate synthetase I (CPS I) can lead to a build-up of ammonia in the body, a condition known as hyperammonemia. Hyperammonemia can have severe consequences, including brain swelling, seizures, coma, and even death if not properly managed. This is because ammonia is a highly toxic substance that can damage the central nervous system and other vital organs. Individuals with certain inborn errors of metabolism or liver disease may be particularly susceptible to CPS I deficiency, which can disrupt the normal functioning of the urea cycle and result in the accumulation of harmful levels of ammonia in the body. Prompt diagnosis and appropriate treatment, such as dietary modifications and medication, are crucial for managing CPS I deficiency and preventing the potentially life-threatening effects of hyperammonemia.
• Analyze the factors that regulate the activity of carbamoyl phosphate synthetase I (CPS I) and explain how these factors contribute to the enzyme's role in protein metabolism.
  • The activity of carbamoyl phosphate synthetase I (CPS I) is regulated by various factors, including the availability of substrates (ammonia and bicarbonate), allosteric modifiers, and hormonal signals. The availability of these substrates is crucial, as CPS I catalyzes the condensation of ammonia and bicarbonate to form carbamoyl phosphate, the first and rate-limiting step in the urea cycle. Allosteric modifiers, such as N-acetylglutamate, can enhance the enzyme's activity, while other factors may inhibit it. Hormonal signals, particularly those related to the regulation of nitrogen balance and protein metabolism, can also influence CPS I activity. By responding to these regulatory mechanisms, CPS I is able to adjust its function in accordance with the body's changing metabolic needs, ensuring the efficient disposal of excess nitrogen and maintaining overall protein homeostasis. This tight regulation of CPS I is essential for preventing the accumulation of toxic ammonia and supporting the proper functioning of the urea cycle, which is a critical component of protein metabolism.

Related terms

Urea Cycle:

The urea cycle, also known as the ornithine cycle, is a metabolic pathway that converts toxic ammonia into urea, which can be safely excreted by the kidneys.

Ammonia:

Ammonia is a toxic byproduct of protein metabolism that must be converted into a less toxic compound, such as urea, for elimination from the body.

Bicarbonate:

Bicarbonate is a chemical compound that acts as a buffer in the body, helping to maintain the appropriate pH level and providing a substrate for the CPS I enzyme.