Discuss metabolism of amino acids, focusing on energy production.
Key Processes: Transamination and subsequent reactions in the liver.
Amino Acids in Muscle
Amino acids are vital for protein synthesis.
Example: Alanine metabolism.
Alanine Structure
Basic structure: N-C-C backbone.
Contains NH3+ group, alpha hydrogen, and a methyl group.
Zwitterion form has both positive and negative charges.
Transamination Process
Alanine reacts with alpha-ketoglutarate (derived from glutamate).
Catalyzed by enzyme: Alanine aminotransferase (ALT).
Involves pyridoxal phosphate (derived from Vitamin B6) as a coenzyme.
Swap groups: Alanine’s amine group is transferred to alpha-ketoglutarate.
End products: Pyruvate and Glutamate.
Key Points
Transamination is the transfer of an amine group from an amino acid to a keto acid.
ALT enzyme catalyzes the transfer via a Schiff base linkage.
Pyruvate Pathways
Pyruvate can convert into:
Lactic acid (Cori Cycle).
Acetyl-CoA (Krebs cycle, leading to ATP production).
Cori Cycle: Lactic acid -> Pyruvate in the liver -> Glucose (via gluconeogenesis).
Glutamate Pathway
Transports from muscle to liver.
Undergoes oxidative deamination by glutamate dehydrogenase.
Produces NADPH (reducing agent for fatty acid synthesis).
Releases toxic ammonia, which converts to urea in the mitochondria.
End product: Alpha-ketoglutarate.
Oxidative Deamination
Removal of amine group from glutamate, forming ammonia.
Ammonia combines with a proton -> Ammonium -> Urea Cycle.
Results in production of Alpha-ketoglutarate.
Aspartate Transamination
Aspartate reacts with alpha-ketoglutarate.
Catalyzed by Aspartate aminotransferase (AST).
Produces oxaloacetate and glutamate.
Significance
Oxaloacetate enters the Krebs cycle.
Reversible reactions allow interconversion of amino acids and Krebs cycle intermediates.
Broader Impacts of Amino Acid Metabolism
Can use amino acids for ATP production or glucose production (gluconeogenesis).
Key amino acids: Alanine, Aspartate, Glutamate.
Enzyme Locations and Diagnostic Value
ALT and AST enzymes found in heart, skeletal muscles, and liver.
Elevated levels in blood tests can indicate tissue damage (e.g., myocardial infarction, liver damage).
Other markers: Elevated creatine kinase and troponin levels.
Summary
Amino acid metabolism involves intricate processes in muscle and liver cells, significantly contributing to energy homeostasis and diagnosis of tissue damage.