Urea Synthesis And Regulation: The First Step In Nitrogen Metabolism

Urea Synthesis And Regulation: The First Step In Nitrogen Metabolism

Question 1. Describe the synthesis of urea and add a note on its regulation.
Answer:

Synthesis of Urea Regulation:

1. Carbamoyl phosphate synthase -1.
   • It is involved in the first reaction of the urea cycle.
   • Activated by N-acetylglutamate which is synthesized from glutamate and acetyl CoA by synthase.
   • It’s regulation.
     • Increased level of arginine increases N-acetyl glutamate (NAG)
     • The protein-rich diet increases NAG.
2. Other enzymes of the urea cycle.
   • Controlled by the concentration of their respective substrates.

Question 2. Describe the different processes of catabolism of amino acids. Mention the different fates of the carbon skeleton of amino acids after catabolism.
Answer:

Catabolism of amino acids:

• Amino acids undergo transamination and deamination to liberate ammonia.

Transamination Definition:

• The transfer of an amino group from an amino to a keto acid is known as transamination.

Enzymes involved:

• Group of transaminases.

Enzymes Features:

• Enzymes require pyridoxal phosphate for their activity.
• Enzymes are specific for specific amino acids.
• Only amino groups are transferred in the reaction without any liberation of ammonia.
• It is a reversible reaction.
• It involves the catabolism of amino acids as well as the synthesis of non-essential amino acids.
• It uses, excess of amino acids for energy production.
• It results in concentrating nitrogen in glutamate.
• All amino acids with some exception undergoes transamination.
• It is not restricted to a-amino groups.
• Enzymes involved in this reaction are used for diagnostic am! prognostic purposes.

Enzymes  Mechanism:

1. The amino group is transferred to the coenzyme pyridoxal phosphate.
   • Results in the formation of pyridoxamine phosphate.
2. The amino group is transferred from pyridoxamine phosphate to a keto acid.
   • Produces a new amino acid.

2. Deamination Definition:

• The removal of amino groups from the amino acids as NH3 is deamination.

Deamination Types:

1. Oxidative deamination:
   • It is the liberation of free ammonia from the amino group of amino acids along with oxidation.
   • Glutamate dehydrogenase.
     • It catalyzes glutamate by oxidative deamination to liberate ammonia.
   • Amino acid oxidases.
     • They act on corresponding amino acids to produce cx-koto acids and NH3.
2. Non-oxidative determination:
3. It is the deamination of amino acids without undergoing oxidation
   • Amino acid dehydrases.
     • Hydroxy amino acids undergo non-oxidative deamination by PEP-dependent dehydrases.
   • Amino acid desulfhydrases.
     • Sulfur amino acids undergo non-oxidative deamination by desulfhydrases.
4. Mislidases.
   • It acts on histidine to undergo non-oxidative deamination.

Fates of the carbon skeleton of amino acids:

• Generation of energy.
• Glucose synthesis
• Formation of fat or ketone bodies.
• Production of non-essential amino acids.