Dr. Nagla El-Melegy: Protein Metabolism

Amino Acids

• Amino acids are organic acids that contain an NH2 group.
• They are composed of carbon, hydrogen, oxygen, and nitrogen.
• Chains of amino acids are classified as:
  • Peptides: fewer than 50 amino acids
  • Dipeptides: 2 amino acids
  • Tripeptides: 3 amino acids
  • Polypeptides: more than 10 amino acids
  • Proteins: more than 50 amino acids (typically 100 to 10,000 amino acids linked together)

Transamination

• Transamination is the reversible transfer of an amino group (in the form of ammonia) from an α-amino acid to an α-keto acid.
• It forms a new amino acid and a new α-keto acid.
• This process occurs mostly in the liver and kidney.
• Transamination involves both catabolism (degradation) and anabolism (synthesis) of amino acids.
• It diverts excess amino acids towards energy generation.
• The amino acids undergo transamination to finally concentrate nitrogen in glutamate.

Metabolism of Amino Acids

• Amino acids undergo certain common reactions, including transamination followed by deamination for the liberation of ammonia.
• This process is involved in the production of non-essential amino acids.
• The purpose of oxidative deamination is to provide NH3 for urea synthesis and α-keto acids for a variety of reactions, including energy generation.

Aminotransferases

• Aminotransferases are active both in the cytoplasm and mitochondria.
• They catalyze transamination reactions, where α-ketoglutarate acts as an amino group acceptor.
• The reaction involves the transfer of an amino group from an amino acid to an α-keto acid, resulting in a new amino acid and a new keto acid.