This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: miscellaneous, Subject name: Biochemistry
[{'content': 'Ochronosis is \nSelect and explain. \nA. Alkaptonuria, B. Isovaleric aciduria, C. Phenylketonuria, D. Tyrosinemia', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The metabolic defect in alkaptonuria is a defective homogentisate oxidase (EC 1.13.11.5), the enzyme that catalyzes reaction 3 of. The urine darkens on exposure to air due to oxidation of excreted homogentisate. Late in the disease, there is ahritis and connective tissue pigmentation (ochronosis) due to oxidation of homogentisate to benzoquinone acetate, which polymerizes and binds to connective tissue.Reference: Harper biochemistry, 30th edition, page no 304', 'role': 'assistant'}]