Urea Cycle

Enzymes

• AT = Aminotransferase = transaminase
• GDH = Glutamate dehydrogenase
  • Requires NAD(P)⁺ and H₂O
• CPS = Carbamoyl phosphate synthase
  • Requres 2 ATP
• OTC = Ornithine transcarbamoylase
• AS Synthase = Argininosuccinate synthase
• ASase = Arginosuccinase
• PC = Pyruvate carboxylase = enzyme in glucogenesis.
• Fumarate → Malate → Oxaloacetate uses enzymes in krebs cycle.

Deamination of N-terminal Amine

• Aminotransferase
  • Takes N-terminal amine of amino acid and places it on αKG to make glutamate. Aka. Transamination.
  • Requires PLP (pyridoxal-5-phosphate), which is derived from pyridoxine (vitamin B₆).
• Glucose-alanine cycle
  
  • Amino acids in muscle passes amino group to alanine, which travels to liver and passes the amino group on to glutamate.
• Glutamate dehydrogenase
  • Accepts either NAD⁺ or NADP⁺.
  • Activated by NAD⁺, ADP, Leucine.
  • Inhibited by NADH, GTP.
• Amino acid oxidase
  • Amino acid → NH₄⁺ + α-keto acid (uses FAD and H₂O)
• Some amino acids are deaminated non-oxidatively (something other than α-keto acid results)

Urea Cycle

• What goes in: NH₄⁺ + HCO₃^- + Aspartate
• What comes out: Urea + Fumarate
  • Urea gets one amino group from NH₄⁺, the other form aspartate, and the carbon atom from HCO₃^-. Fumarate is derived from the carbon skeleton of aspartate.
• 3 ATP hydrolyzed: CPS converts 2ATP → 2ADP. AS Synthase converts ATP → AMP.