Gluconeogenesis of Amino Acids

[rohudc]

ALT converts alanine to pyruvate using α-ketoglutarate. How is this reaction useful when α-ketoglutarate will anyway be converted to pyruvate?

This is solely in the context of producing glucose from glucogenic amino acids. When amino acids are the only option, the body uses them but if they are going to need TCA cycle intermediates to produce other TCA cycle intermediates/pyruvate, I don’t see any net gain.

Edited March 12, 2017 by rohudc

[BabcockHall]

Would you mind defining ALT? I will assume that it is an aminotransferase. IMO your assumption about alpha-ketoglutarate is not correct: alpha-ketoglutarate will be converted into glutamate by the transamination that converts alanine into pyruvate. When the body has to use amino acids as fuel, something has to happen to the nitrogen. What is it? Your answer to this question should help answer your question.

[rohudc]

Would you mind defining ALT? I will assume that it is an aminotransferase. IMO your assumption about alpha-ketoglutarate is not correct: alpha-ketoglutarate will be converted into glutamate by the transamination that converts alanine into pyruvate. When the body has to use amino acids as fuel, something has to happen to the nitrogen. What is it? Your answer to this question should help answer your question.

 

Yup, ALT stands for alanine aminotransferase.

 

Omg, so glutamate dehydrogenase would act on the glutamate produced and give us alpha-ketoglutarate (eventually glucose) and NH₃ enters the urea cycle. Am I right?

Edited March 13, 2017 by rohudc

[BabcockHall]

 

Yup, ALT stands for alanine aminotransferase.

 

Omg, so glutamate dehydrogenase would act on the glutamate produced and give us alpha-ketoglutarate (eventually glucose) and NH₃ enters the urea cycle. Am I right?

 

I agree that glutamate can be dehydrogenated and the ammonia will enter the urea cycle. This allows the alpha-ketoglutarate to pick up additional amino groups from other amino acids to be degraded (although some could also enter into gluconeogenesis). What do you think that the fate of pyruvate (generated from alanine) is?

Edited March 13, 2017 by BabcockHall

[rohudc]

 

I agree that glutamate can be dehydrogenated and the ammonia will enter the urea cycle. This allows the alpha-ketoglutarate to pick up additional amino groups from other amino acids to be degraded (although some could also enter into gluconeogenesis). What do you think that the fate of pyruvate (generated from alanine) is?

 

Pyruvate will enter gluconeogenesis and give us the required glucose during fasting. Isn't it? So yup, now I get it, there clearly is a net gain in using amino acids as a fuel.

[BabcockHall]

Yes, pyruvate can be converted into glucose by gluconeogenesis. Another way to think about alanine and gluconeogenesis is to ponder the similarities of lactate versus alanine. For example both can be converted into pyruvate in one step.

EDT

You might want to look up the glucose-alanine cycle in your textbook.

Edited March 13, 2017 by BabcockHall

[rohudc]

Oh okay!

 

I can't thank you enough for your help!

That question was bothering me for quite some time and many people to whom I asked had no clue.