Aspartate aminotransferase catalyzes this reaction: Alanine aminotransferase cat

Question

Aspartate aminotransferase catalyzes this reaction:

Alanine aminotransferase catalyzes this reaction:

Be sure to look up the structures of these compounds if you don't know them. Two biochemists are investigating the synthesis of glucose from dietary amino acids. Biochemist 1 obtains 4-[14C]aspartate (aspartate that has 14C at the sidechain carboxyl) and feeds it to rats. After sacrificing the rats, he is unable to detect any significant amounts of 14C in glucose. Biochemist 2 obtains 3-[14C]alanine (alanine that is labeled at the sidechain methyl group) and feeds it to rats. After sacrificing the rats, she finds that the glucose isolated from the rats does contain significant amounts of 14C-glucose.  

Consider the result obtained by Biochemist 2 in the experiment described above. Where is the 14C located in the glucose isolated by Biochemist 2?

Explanation / Answer

Answer: Option A is correct

Explanation:

Alanine is converted to pyruvate which enters gluconeogenesis pathway to produce glucose.

The third carbon atom of Ala is labeled which becomes methyl group of pyruvate.

In glycolysis, if we label C1 of glucose, it ends up in the methyl group of pyruvate.

Reciprocally, if we label the methyl group of pyruvate, it ends up as C1 in glucose.

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