Glucose-Alanine Cycle

The glucose-alanine cycle is an important cycle in muscle, where glycolysis is active, because it helps to remove toxic ammonia as it builds up (Figure 20.14). The cycle operates as follows:

1. Glutamate dehydrogenase links ammonia to -ketoglutarate to form glutamate.

2. Glutamate donates its amine group to pyruvate (from glycolysis) to form alanine and -ketoglutarate.

3. Alanine is transported to the liver, where it loses the amine group by a reversal of the previous processes, yielding ammonia for urea synthesis and pyruvate.

4. Pyruvate undergoes gluconeogenesis to form glucose, which is released to the blood and travels back to the muscles.

Thus, muscle gets rid of ammonia and pyruvate and receives glucose (ultimately) in exchange.