The salvage pathway recycles free purine bases using PRPP as the ribose-phosphate donor. Which pair of reactions is catalyzed by hypoxanthine-guanine phosphoribosyltransferase (HGPRT)?
- A Hypoxanthine plus PRPP to IMP, and guanine plus PRPP to GMP ✓
- B Adenine plus PRPP to AMP, and guanine plus PRPP to GMP
- C Xanthine plus PRPP to XMP, and hypoxanthine plus PRPP to IMP
- D Guanine plus PRPP to GMP, and adenine plus PRPP to ATP
Correct answer: A. Hypoxanthine plus PRPP to IMP, and guanine plus PRPP to GMP
Explanation
HGPRT salvages both hypoxanthine to IMP and guanine to GMP. Adenine is salvaged by a separate enzyme, adenine phosphoribosyltransferase (APRT), making options B and D incorrect. Xanthine has no salvage route to XMP via HGPRT; it is simply oxidized further by xanthine oxidase. This division of labor between HGPRT and APRT explains why HGPRT deficiency spares adenine recycling but devastates hypoxanthine and guanine salvage.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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