Ornithine transcarbamylase

Definition

Ornithine transcarbamylase (OTC) is an enzyme that catalyzes the reaction between ornithine and carbamoyl phosphate to produce citrulline, playing a crucial role in the urea cycle. This enzyme helps convert excess nitrogen from amino acid metabolism into urea for excretion, effectively linking amino acid and protein metabolism to nitrogen removal in the body.

5 Must Know Facts For Your Next Test

1. Ornithine transcarbamylase is primarily found in the mitochondria of liver cells, where it plays a key role in the urea cycle.
2. Deficiency in OTC can lead to hyperammonemia, a condition characterized by elevated levels of ammonia in the blood, which can cause severe neurological damage.
3. OTC is regulated by substrate availability; increased levels of its substrates can enhance its activity, while higher concentrations of intermediates can inhibit it.
4. The activity of ornithine transcarbamylase is essential for removing excess nitrogen derived from amino acid breakdown, thus preventing toxicity.
5. Ornithine transcarbamylase deficiency is inherited in an X-linked manner, meaning it predominantly affects males and can be passed down through carrier females.

Review Questions

• How does ornithine transcarbamylase contribute to the urea cycle and nitrogen metabolism?
  • Ornithine transcarbamylase plays a critical role in the urea cycle by catalyzing the reaction that combines ornithine with carbamoyl phosphate to form citrulline. This step is essential for converting toxic ammonia, produced from amino acid breakdown, into urea for safe excretion. By facilitating this reaction, OTC helps maintain nitrogen balance in the body and prevents toxic accumulation.
• Discuss the implications of ornithine transcarbamylase deficiency on human health and how it affects overall amino acid metabolism.
  • Deficiency in ornithine transcarbamylase can lead to serious health issues such as hyperammonemia, where ammonia builds up in the blood due to ineffective conversion to urea. This condition can result in neurological problems and can be life-threatening if not managed properly. The inability to effectively process nitrogen from amino acids disrupts overall metabolism and requires dietary management to limit protein intake.
• Evaluate how ornithine transcarbamylase regulation affects metabolic processes involving amino acids and nitrogen waste elimination.
  • The regulation of ornithine transcarbamylase is crucial for balancing amino acid metabolism and nitrogen waste elimination. When levels of substrates like carbamoyl phosphate are high, OTC activity increases to help process excess nitrogen effectively. Conversely, when intermediates accumulate due to disruptions or deficiencies, OTC activity may decrease, leading to elevated ammonia levels. This regulation highlights the enzyme's central role in maintaining metabolic homeostasis and preventing toxicity from nitrogenous waste.

Related terms

Urea Cycle:

A series of biochemical reactions that occur in the liver, converting ammonia and other nitrogenous wastes into urea, which is then excreted by the kidneys.

Citrulline: An amino acid produced during the urea cycle as a result of the reaction between ornithine and carbamoyl phosphate, eventually leading to the formation of arginine.

Carbamoyl Phosphate: A molecule that serves as a key substrate in the urea cycle, formed from ammonia and bicarbonate, and used by OTC to produce citrulline.