Which enzyme catalyzes the conversion of hypoxanthine to xanthine in the purine degradation pathway?

Explanation

## Purine Degradation Pathway **Key Point:** Xanthine oxidase is the enzyme responsible for the final two oxidation steps in purine catabolism: conversion of hypoxanthine → xanthine → uric acid. ### Enzyme Function Xanthine oxidase is a molybdenum-containing flavoprotein that catalyzes: 1. Hypoxanthine + O₂ → Xanthine + H₂O₂ 2. Xanthine + O₂ → Uric acid + H₂O₂ ### Clinical Significance - **Allopurinol and febuxostat** are xanthine oxidase inhibitors used to treat gout by reducing uric acid production - Deficiency of xanthine oxidase is rare but leads to xanthinuria (accumulation of xanthine in urine) - The enzyme is the rate-limiting step in uric acid formation **High-Yield:** Xanthine oxidase is the ONLY enzyme that produces uric acid — this is why xanthine oxidase inhibitors are first-line therapy for chronic gout management [cite:KD Tripathi 8e Ch 32] ### Pathway Overview ``` Adenosine/Guanosine ↓ (Deaminase) ↓ Inosine/Guanine ↓ (Phosphorylase) ↓ Hypoxanthine → [Xanthine Oxidase] → Xanthine → [Xanthine Oxidase] → Uric Acid ```