This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Proteins and Amino Acids, Subject name: Biochemistry
Branched chain ketoaciduria is a defect of catabolism of all the following aminoacids except- 
Select and explain. 
A. Leucine, B. Isoleucine, C. Valine, D. Methionine
D: Methionine
Answer: D: Methionine 
Explanation: Ans. is 'd' i.e., Methionine * Branched chain ketoaciduria or Maple Syrup Urine Disease (MSUD) is caused by a defect of branched chain keto acid dehydrogenase enzyme complex (BCKD). BCKD catalyses the second step of catabolism of branched chain amino acids - Leucine, Isoleucine and Valine.