How does the aminotransferase, whose activity you have demonstrated in the lab,

Question

How does the aminotransferase, whose activity you have demonstrated in the lab, operate in the process of nitrogen excretion from muscle (See Figure 2 in lab manual)? To answer this question, identify the reactions involved, beginning with the uptake of free ammonium ions in muscle and ending with the uptake of the ammonia in the urea cycle. Your answer should include mention of 3 and 6 carbon backbone cycling and how energy originating in the liver is made available for work to be done in the muscle.

Explanation / Answer

Aminotransferases are the transaminases that catalyze the transfer of ammonia and its incorporation into urea cycle. Glutamate and alpha-ketoglutarate are the two compounds that involve as the donor/acceptor in the transamination reactions. The 3 carbon molecule alanine and pyruvate get converted to glucose. In the muscle the pyruvate molecule is transaminated to alanine, giving an additional route of nitrogen transport from the muscle into the liver. Alanine transaminase is responsible for the transfer of muscle carbon and nitrogen into the liver. In the liver, alanine transaminase transfers the ammonia to alpha-ketoglutarate and generates the pyruvate. The pyruvate molecule gets into gluconeogenesis and releases glucose into the blood. This process is known as the glucose-alanine cycle. The amino group transported from the muscle to liver gets incorporated into alanine and subsequently gets converted to urea in the urea cycle and gets excreted out.The energy that is produced in the muscle is stored in the form of lactate and which enters the liver gets converted to pyruvate and subsequently to urea and gets excreted out.

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