Lecture: Amino Acid Metabolism

Overview

• Focus on amino acids metabolism and their utilization for energy.
• Key processes in muscle and liver:
  • Transamination
  • Role of enzymes and intermediates like alanine, alpha-ketoglutarate, and glutamate.

Amino Acids in Muscle

• Amino Acids are crucial for protein synthesis in muscles.
• Example: Alanine structure
  • Contains NH3 group (+ charge), alpha hydrogen, methyl group, and carboxyl group.
  • Exists in zwitterion form (neutral overall charge).

Transamination Process

• Alanine reacts with Alpha-ketoglutarate:
  • Catalyzed by: Alanine Aminotransferase (transaminase enzyme with pyridoxal phosphate from Vitamin B6).
  • Transaminase swaps the amine group of alanine with the oxygen of alpha-ketoglutarate.
  • Products: Pyruvate and Glutamate

Outcomes of Transamination

• Pyruvate can:
  • Convert to Lactic Acid or Acetyl CoA.
  • Acetyl CoA enters Krebs Cycle → Electron Transport Chain → ATP production.
• Lactic Acid enters the Cori Cycle:
  • Converted to Pyruvate in the liver by lactate dehydrogenase.
  • Pyruvate → Glucose 6-phosphate → Glucose (via glucose 6-phosphatase).
  • Supports Gluconeogenesis.

Glutamate in the Liver

• Glutamate from muscle undergoes Oxidative Deamination:
  • Catalyzed by Glutamate Dehydrogenase with NADP+ to NADPH conversion.
  • Produces: Alpha-ketoglutarate and Ammonia (toxic, converted to ammonium).
  • Ammonium enters mitochondria for the urea cycle.

Aspartate and Alpha-ketoglutarate Reaction

• Aspartate reacts with Alpha-ketoglutarate:
  • Catalyzed by: Aspartate Aminotransferase.
  • Swaps amine group from aspartate to alpha-ketoglutarate.
  • Produces: Glutamate and Oxaloacetate

Significance of Amino Acid Metabolism

• ATP Production and Gluconeogenesis:
  • Amino acids can be converted into Krebs Cycle intermediates.
  • Can lead to ATP production or glucose generation.
  • Gluconeogenesis: Conversion of non-carb sources (amino acids) to glucose.

Clinical Relevance

• Elevated enzyme levels (AST, ALT) in blood tests may indicate:
  • Liver or cardiac muscle damage.
  • Potential myocardial infarction if accompanied by high creatine kinase and troponin levels.

Next Steps

• Upcoming discussion: Urea Cycle

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These notes cover the key processes of amino acid metabolism, focusing on transamination processes, the role of specific enzymes and molecules, and the clinical significance of enzyme levels. Further exploration in subsequent lectures will continue with the urea cycle.