Rate limiting enzyme
Transport of ammonia by alanine
- In the liver, alanine is transaminated by alanine aminotransferase to pyruvate with the amino group being transferred to α-ketoglutarate to form glutamate. Almost all aminotransferase enzymes use α-ketoglutarate as the amino group acceptor.
- Thus, amino groups are funneled into glutamate during protein catabolism.
- Glutamate is further metabolized by the enzyme glutamate dehydrogenase, which liberates free ammonia and regenerates α-ketoglutarate.
- Ammonia then enters the urea cycle to form urea, the primary disposal form of nitrogen in humans.
- Urea subsequently enters the blood and is excreted in the urine.
Cori cycle & Cahill cycle
Lactate/alanine is transported to the liver, where it is converted into glucose. It is then transported back to the muscles for energy production.