LSM2101 Part II Lecture 3 The Urea Cycle and Disorders

Lecture 3: Urea Cycle / Ornithine Cycle

• Urea: NH2-CO-NH2 (first N is from Asp, the other one is from ammonia, C is from CO2)
• Carbamoyl Phosphate synthesis is a rate-limiting step

•  Regulation:  Carbamoyl Phosphate Synthetase
• CP I: ammonia dependent, N-acetylglutamate -> activator, mitochondrial
• CP II: Amide-N of glutamine, independent from  N-ace glu, cytoplasmic
• N-acetylglutamate: from Glu + Arg using Acetylglutamate Synthase (N-acteyl Transferase)

• Kreb's Bicycle

 

•  Metabolic Disorder - Hyperammonemia (Defects in enzymes)
• Hyperammonemia Type I: Carbamoyl Phosphate Synthetase I
• Hyperammonemia Type II: Ornithine Transcarbamoylase
• Citrullinemia: Argininosuccinate Synthetase
• Argininosuccinic aciduria/acidemia: Argininosuccinate lyase/Argininosuccinase
• Argininemia: Arginase

• Nitrogen Disposal
• Ureotelic-Urea: Mammals
• Ammonotelic-Ammonia: Fishes
• Uricotelic-Ric Acid: Birds