LSM2101 Part II Lecture 2 Ammonia Production and Detoxification

Conversion of AA to Keto Acids

• Oxidative Deamination
• L-AA Oxidase + FMN + Catalase

• L-Glutamate Dehydrogenase + NAD+

• Transamination
• Mechanism: 
• Transfer of amine group from AA to PLP: 1. Transamination 2. Tauromerization 3. Hydrolysis
• Transfer of amine group from PLP to Keto-Acid: reverse of above

• General: 

• Aspartate-Aminotransferase (Glutamate-oxaloacetate transaminase)

• Alanine-Aminotransferase (Glutamate-pyruvate Transaminase)

• AST & AST: indication of damaged cells if found in blood serum.
• Trasndeamination: Transamination + Oxidative Deamination

• Importance:
• Funneling to glutamate for conversion to ammonia.
• Synthesis of non-essential amino acids.
• Non-Oxidative Deamination
• Ammonia Lyases

• Specific Deaminases:
• Serine dehydratase (L-serine hydrolase)

• Threonine dehydratase

• Cysteine desulfhydrase

Excretion of Ammonia

• AA -> Glu (1 eq NH3) -> Gln (2 eq NH3): happens in everywhere, transported to kidney or liver.
• Gln (2 eq NH3) -> Glu (1 eq NH3) + NH4+: only happens in kidney and liver.
• Ion-trapping mechanism: since NH4+ can't cross cell's membrane, ammonium ions in kidney lumen cannot enter kidney cells.