This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Fuel in Fed, Fasting and Starvation, Subject name: Biochemistry
Creatinine is the breakdown product of: 
Select and explain. 
A. Adenosine triphosphate, B. Purine nucleotides, C. Pyrimidine nucleotides, D. Creatine phosphate
D: Creatine phosphate
Answer: D: Creatine phosphate 
Explanation: Creatinine is the breakdown product of creatine phosphate This reaction occurs in muscles & does not involve any enzyme.