This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
A key gluconeogenic amino acid is: 
Select and explain. 
A. Alanine, B. Serine, C. Valine, D. Tyrosine
A: Alanine
Answer: A: Alanine 
Explanation: Alanine is a key gluconeogenic amino acid. The rate of hepatic gluconeogenesis from alanine is far higher than from all other amino acids. The capacity of the liver for gluconeogenesis from alanine does not reach saturation until the alanine concentration reaches 20 to 30 times its normal physiologic level.
Ref: Harper’s illustrated biochemistry. 30th edition page no: 289