Amino Acid Metabolism

Overview

• Focus on how amino acids are metabolized and utilized for energy.
• Key processes include transamination and the role of specific amino acids in muscle and liver.

Amino Acids and Their Structures

• Amino acids are essential for protein synthesis, found in muscle.
• Example: Alanine
  • Basic structure: NH3 group, alpha hydrogen, methyl group (CH3), carboxyl group (COOH).
  • Zwitterion form: overall neutral with + and - charges.

Key Process: Transamination

• Definition: Transfer of an amine group from one amino acid to a keto acid.
• Example Reaction: Alanine + Alpha-ketoglutarate.
  • Alanine transfers its amino group to alpha-ketoglutarate.
  • Catalyzed by Alanine Aminotransferase (ALT).
  • Forms Pyruvate and Glutamate.

Enzymatic Mechanism

• Pyridoxal Phosphate: vitamin B6 derivative involved in the transamination process.
• Enzyme linked to pyridoxal phosphate via Schiff base linkage (imine formation).
• Reaction summary:
  • Alanine (NH2) → Pyruvate
  • Alpha-ketoglutarate (O) → Glutamate.

Fate of Pyruvate and Glutamate

1. Pyruvate
   • Can be converted to:
     • Lactic acid (in muscles)
     • Acetyl CoA (enters Krebs cycle).
   • Both pathways lead to ATP production.
2. Glutamate
   • Transported to liver for further processing.
   • In liver: undergoes oxidative deamination.
   • Enzyme: Glutamate Dehydrogenase.
   • Converts glutamate to alpha-ketoglutarate and releases ammonia (toxic).

Oxidative Deamination

• Process: Removal of the amine group from glutamate.
• Generates NADPH (reducing agent) via NADP+ to NADPH reduction.
• Result: Conversion to alpha-ketoglutarate and release of ammonia.

Corey Cycle

• Lactic Acid Cycle:
  • Lactic acid from muscles → blood → liver.
  • Converted back to pyruvate by Lactate Dehydrogenase.
  • Pyruvate can then be converted to glucose through gluconeogenesis.

Importance of Transamination and Deamination

• Amino acids can produce energy (ATP) or glucose (gluconeogenesis).
• Significant for energy metabolism, especially in starvation or low-carb conditions.

Enzymatic Activity in Tissues

• ALT and AST enzymes found in:
  • Liver, cardiac muscle, skeletal muscle.
• Elevated enzyme levels in blood tests can indicate:
  • Liver damage (elevated ALT)
  • Cardiac damage (elevated AST).

Conclusion

• Amino acid metabolism involves complex inter-conversions between amino acids and keto acids.
• Essential for maintaining energy balance and metabolic homeostasis.

Next Topic

• Upcoming discussion on the Urea Cycle.