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Transcript of GLUCOSE-ALANINE CYCLE
Also known as Cahill cycle or alanine cycle.A series of reactions in which amino groups from the muscle are transported to the liver.
It is quite similar to the Cori cycle.
In muscle, pyruvate is converted to alanine, while in liver, alanine is converted to pyruvate. When this process occur simultaneously, it is known as glucose-alanine cycle.
Anaerobic (no or decrease in oxygen)
During extended periods of fasting (eg baby not feeding well, Ramadan fasting/puasa bulan Ramadhan), skeletal muscle is degraded as an alternative source of energy.
Alanine is a nonessential amino acid.
Alanine is found in a wide variety of foods, but is particularly concentrated in meats.
Alanine is the major amino acid present when muscle (protein) is degraded.
Good sources of alanine include:
Animal sources: meat, seafood, dairy products, eggs, fish, gelatine.
Vegetarian sources: beans, nuts, seeds, soy,, brown rice, corn, legumes, whole grains
THE END :)
PRODUCTION OF ALANINE
Directly from protein degradation
Transamination of pyruvate by alanine transaminase, ALT (also referred to as serum glutamate-pyruvate transaminase, SGPT).
Glutamate is synthesized by the reductive amination of α-ketoglutarate catalyzed by glutamate dehydrogenase
Glutamate arises by aminotransferase reactions, with the amino nitrogen being donated by a number of different amino acids glutamate is a general collector of amino nitrogen
Reactions in skeletal muscle:
In muscle cells and other peripheral tissues, glycolysis produces pyruvate.
Pyruvate can be transaminated to alanine.
The transamination reaction requires an α-amino acid as donor of the amino group, generating an α-keto acid in the process.
This reaction is catalyzed by alanine transaminase, ALT.
The alanine then enters the blood stream and is transported to the liver.
Alanine is returned to the liver for gluconeogenesis.
Reactions in liver:
Within the liver, alanine is converted back to pyruvate by deamination.
Pyruvate is a source of carbon atoms for gluconeogenesis.
Gluconeogenesis converts pyruvate to form glucose.
The newly formed glucose can then enter the blood for delivery back to the muscle.
This pathway is termed the glucose-alanine cycle.
The glucose-alanine cycle occurs in skeletal muscle to eliminate nitrogen while replenishing (renewing) the energy supply for muscle.
The amino group transported from the muscle to the liver in the form of alanine, is converted to urea in the urea cycle and excreted.
Alanine is converted back to pyruvate which is then a source of carbon atoms for gluconeogenesis
The key feature of the cycle is that in 1 molecule, alanine, peripheral tissue exports pyruvate and ammonia to the liver, where the carbon skeleton is recycled and most nitrogen eliminated.
Harpers Biochemistry 24th edition