This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of nucleic acids, Subject name: Biochemistry
What supplies ammonia to liver? 
Select and explain. 
A. Arginine, B. Alanine, C. Lactate, D. Pyruvate
B: Alanine
Answer: B: Alanine 
Explanation: Aminotransferases (transaminases) catalyze the general reaction shown above. The most common compounds involved as a donor/acceptor pairs in transamination reactions are glutamate and 2-oxoglutarate (a-ketoglutarate). Alanine transaminase has an impoant function in the delivery of skeletal muscle carbon and nitrogen (in the form of alanine) to the liver. In skeletal muscle, pyruvate is transaminated to alanine, thus affording an additional route of nitrogen transpo from muscle to liver. In the liver, alanine transaminase transfers the ammonia to 2-oxoglutarate and regenerates pyruvate. The pyruvate can then be diveed into glucon Ref: <a href="