A patient complains of knee pain. Routine investigations are unremarkable and still, the patient is unsatisfied. Urine turns black on standing, what is the enzyme involved?: (A) Homogentisate oxidase, (B) Xanthine oxidase, (C) Methyl malonate oxidase, (D) Phenyl pyruvate oxidase
Answer is A. Alkaptonuria - Due to deficiency of Homogentisate dioxygenase/ oxidase (requires Iron) Fresh urine is normal in colour On standing or on exposure to air - turns Black - Homogentisic acid accumulated - get oxidised - gives rise to Black urine - Homogentisic acid gets polymerized in body forming ALKAPTON BODIES, which gets accumulated in: Cailages - Nose, ear pinna, interveebral disc Connective tissue has bluish black colour. Patient develops ahralgia & ahritis. - This condition is known as Ochronosis. Ahritis is also known as ochronotic ahritis - Benedict 's test is positive due to homogentisic Acid, which is a Reducing substance - Treatment drug is NITISINONE