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
End product of purine metabolism in non-primate mammals is 
Select and explain. 
A. Uric acid, B. Ammonia, C. Urea, D. Allantoin
D: Allantoin
Answer: D: Allantoin 
Explanation: Allantoin is a major metabolic intermediate in most organisms including animals, plants, and bacteria and is produced as a degradation product of purine nucleobases by urate oxidase (or uricase) from uric acid