Question

List and explain the role of the enzymes needed for the following routing of nitrogen into the urea cycle: Start with a molecule of aspartate in peripheral tissue (e.g., muscle) and end with the nitrogen derived from that original aspartate molecule released as free ammonia in the liver. (Hint: routing should be by the major non-toxic carrier of nitrogen in the blood).

Answer 1

The urea cycle (also known as the ornithine cycle) is a cycle of biochemical reactions that produces urea.

Following enzymes are needed for routing of nitrogen into the urea cycle:-

• Arginosuccinate synthetase
• Arginosuccinase
• Arginase
• carbamyl phosphate synthase
• ornithine transcarbamylase

Function of these enzymes described below:-

1. argininosuccinate synthetase is involved in the production of nitric oxide.
2. Argininosuccinate, Located in liver cytosol, helps in biosynthesis arginine production and release of fumarate.
3. An important ureohydrolase enzyme arginase is a manganese-containing enzyme, which catalyzes the final step in the urea cycle to dispose of toxic ammonia by converting l-arginine to l-ornithine and urea .
4. Ornithine enhances liver function and helps detoxify harmful substances.Ornithine transcarbamoylase (OTC) is an enzyme that catalyzes the reaction of citrulline formation from l-ornithine and carbamoyl phosphate.responsible for 80% of the nitrogen excretion in the body.
5. The main role of the carbamoyl phosphate synthetase I enzyme is to control the first step of the urea cycle,

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