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
In humans, the end product of purine metabolism is uric acid. 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: Humans conve adenosine and guanosine to uric acid. Adenosine is first conveed to inosine by adenosine deaminase. In mammals other than higher primates, uricase conves uric acid to the water-soluble product allantoin. However, since humans lack uricase, the end product of purine catabolism in humans is uric acid. Ref: Rodwell V.W. (2011). Chapter 33. Metabolism of Purine & Pyrimidine Nucleotides. In D.A. Bender, K.M. Botham, P.A. Weil, P.J. Kennelly, R.K. Murray, V.W. Rodwell (Eds), Harper's Illustrated Biochemistry, 29e.