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
[{'content': 'A 30 year old female presents with bluish black discoloration of sclera and pinna for last 4 months. Her urine turns black on standing.\xa0Which of the following enzyme is most likely to be deficient? \nSelect and explain. \nA. Phenylalanine hydroxylase, B. Homogentisate oxidase, C. Tryptophan pyrrolase, D. α-keto\xa0acid\xa0decarboxylase\xa0complex', 'role': 'user'}, {'content': "Answer: B \nExplanation: The metabolic defect in alkaptonuria is a defective homogentisate\xa0oxidase.\nClinical Presentation of Alkaptonuria:\n\nNormal life till 3rd or 4th decade.\nUrine darkness on standing is the only manifestation in children.\nIn adults, ochronosis, i.e. Alkaptone body deposited in intervertebral disk, cartilage of nose, pinna, etc. leading to pigmentation.\nArthritis.\xa0\nNo mental retardation.\xa0\xa0\n\nLaboratory Diagnosis:\n\nAlkalanization increase darkening of urine.\nBenedict's test positive in urine, because homogentisic acid is reducing agent.\nFerric chloride test positive.\nSilver nitrate test positive.\n\nReference- Harper’s illustrated biochemistry. 30th edition page -304", 'role': 'assistant'}]