Alanine cycle
Oxford Dictionary of Biochemistry:
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glucose-alanine cycle
or alanine cycle
a metabolic cycle in which alanine is formed peripherally, e.g. in muscle, by transamination of glucose-derived pyruvate, and is transported to the liver where its carbon skeleton is reconverted to glucose.
a metabolic cycle in which alanine is formed peripherally, e.g. in muscle, by transamination of glucose-derived pyruvate, and is transported to the liver where its carbon skeleton is reconverted to glucose.
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Alanine cycle
The alanine cycle is quite similar to the Cori cycle. When muscles produce lactate during times of decreased oxygen, they also produce alanine. This alanine is shuttled to the liver where it is used to make glucose.
The alanine cycle is less productive than the Cori Cycle, which uses lactate, since a byproduct of energy production from alanine is production of urea. Removal of the urea is energy-dependent,requiring four "high-energy" phosphate bonds (3 ATP hydrolyzed to 2 ADP and one AMP), thus the net ATP produced is less than that found in the Cori Cycle. However, unlike in the Cori Cycle, NADH is conserved because lactate is not formed. This allows for it to be oxidized via the electron transport chain. This pathway requires the presence of alanine aminotransferase, which is restricted to tissues such as muscle, liver, and the intestine. Therefore, this pathway is used instead of the Cori Cycle only when an aminotransferase is present and when there is a need to transfer ammonia to the liver.
Alanine cycle also serves other purposes:
- Recycles carbon skeletons between muscle and liver
- Transports ammonium to the liver and is converted into urea.
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Oxford Dictionary of Biochemistry
Oxford University Press. Oxford Dictionary of Biochemistry and Molecular Biology © 1997, 2000, 2006 All rights reserved.
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