This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous (Bio-Chemistry), Subject name: Biochemistry
Lack of Homogentisate oxidase enzyme causes 
Select and explain. 
A. Phenylketonuria, B. Alkaptonuria, C. Maple syrup urine disease, D. Homocystinuria
B: Alkaptonuria
Answer: B: Alkaptonuria 
Explanation: (B) Alkaptonuria # ALKAPTONURIA: The defective enzyme in alkaptonuria is homogentisate oxidase in tyrosine metabolism. Homogentisate accumulates in tissues & blood, gets oxidized to the corresponding quinones, which polymerize to give black or brown colour. For this reason, the urine of alkaptonuric patients resembles coke in colour.