Which enzyme converts xanthine to uric acid AND hypoxanthine to xanthine in purine catabolism?

• A Guanase (guanine deaminase)
• B Adenosine deaminase
• C Uricase (urate oxidase)
• D Xanthine oxidase ✓

Explanation

Xanthine oxidase (XO) catalyses two consecutive reactions: hypoxanthine → xanthine, and xanthine → uric acid; both reactions produce superoxide radicals as a by-product. XO is the target of allopurinol (irreversible inhibition of oxipurinol) and febuxostat (non-purine selective inhibitor). Uricase, absent in humans, converts uric acid to allantoin and is used therapeutically as rasburicase.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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