Alanine (Cahill) Cycle
The Alanine or Cahill Cycle is the biochemical pathway for shuttling amino groups from the muscle to the liver.
In the muscle, amino groups are produced from the breakdown of amino acids. α-ketoglutarate accepts these amino groups, and is converted into glutamate after accepting an amino group. Glutamate then transfers the amino group to pyruvate, producing alanine in a reaction catalyzed by the enzyme, alanine transaminase, better known as ALT (see Pyruvate Metabolism). Alanine can then exit to the bloodstream to reach the liver.
At the liver, alanine is taken up and converted into pyruvate. This involves the removal of an amino group, catalyzed by alanine transaminase (ALT) working in reverse. The amino groups are transferred to α-ketoglutarate, producing glutamate. Glutamate then contributes the amino groups in ammonia for the Urea Cycle, where they are packaged for elimination. The pyruvate produced in the liver is then used for gluconeogenesis, making glucose. This glucose is exported to the bloodstream, and some of it ends up back in the muscle, finishing the cycle.
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