Amino Acid Metabolism

Introduction

• Focus: Amino acid metabolism
• Specifics: Metabolization and utilization of amino acids for energy
• Processes Discussed: Transamination, oxidative deamination

Amino Acids in Muscle

• Role: Protein synthesis
• Example: Alanine

Structure of Alanine

• NCC backbone
  • NH₃⁺ group
  • Alpha hydrogen
  • Methyl group (for alanine)
  • Carboxyl group

Alanine Transamination

• Partner: α-Ketoglutarate (AKG)
• Enzyme: Alanine Aminotransferase (transaminase)
• Cofactor: Pyridoxal phosphate (derived from vitamin B6)
• Key Reaction: Exchange of amino group from alanine with oxygen from α-ketoglutarate
  • Alanine → Pyruvate
  • α-Ketoglutarate → Glutamate

Transamination Process

• Definition: Transfer of an amino group from amino acid (alanine) to a keto acid (α-ketoglutarate)
• Catalyzed by: Alanine Aminotransferase (ALT)
• Mechanism: Pyridoxal phosphate acts as a carrier

Fate of Pyruvate and Glutamate

Pyruvate

• Muscle cell pathways:
  • Convert to lactic acid (Cori cycle)
  • Convert to Acetyl-CoA (Krebs cycle, Electron Transport Chain)
• Ultimate outcomes:
  • ATP production
  • Gluconeogenesis in the liver (via Cori cycle)
    • Lactic acid → Pyruvate → Glucose-6-Phosphate → Glucose

Glutamate

• Transport to liver:
  • Removal of amino group as ammonia (via Glutamate Dehydrogenase)
  • Ammonia incorporation into urea (Urea cycle)
• Oxidative Deamination Process:
  • NADP⁺ → NADPH
  • Glutamate → α-Ketoglutarate + Ammonia
  • Enzyme: Glutamate Dehydrogenase

Secondary Transamination Example: Aspartate

• Aspartate + α-Ketoglutarate:
  • Enzyme: Aspartate Aminotransferase (AST)
  • Products: Oxaloacetate + Glutamate
• Oxaloacetate Roles:
  • Krebs cycle intermediate
  • Gluconeogenesis precursor

Interconnectedness of Amino Acid Metabolism

• Reversibility of transamination reactions
• Role of various amino acids
• Important intermediates: Pyruvate, Oxaloacetate, Acetyl-CoA, and Krebs cycle intermediates
• Resulting processes: ATP production, gluconeogenesis

Enzyme Distribution

• ALT (Alanine Aminotransferase): Found in liver, muscle, heart
• AST (Aspartate Aminotransferase): Found in liver, muscle, heart
• Clinical significance: Elevated enzyme levels may indicate liver damage or myocardial infarction

Conclusion

• Purpose and significance of amino acid metabolism in energy production and gluconeogenesis
• Next topic: Urea cycle