Elaborate on the Fate of Uric Acid in the Degradation of Purine Nucleotides
Uric acid is the final product of purine nucleotide degradation in humans and other primates. Unlike many other mammals, humans lack the enzyme uricase, which converts uric acid into the more soluble allantoin. This makes uric acid excretion crucial in maintaining nitrogen balance and avoiding pathological conditions.
Purine Degradation Pathway Leading to Uric Acid
- Adenosine and guanosine are broken down into hypoxanthine and xanthine respectively.
- These intermediates are further oxidized by the enzyme xanthine oxidase to form uric acid.
Reactions:
- Hypoxanthine → Xanthine → Uric Acid (both steps catalyzed by xanthine oxidase)
Fate and Excretion
- Uric acid is transported to the kidneys and excreted in urine.
- A small amount is also excreted via the intestines.
Clinical Significance
- Hyperuricemia: Excess uric acid in blood due to overproduction or underexcretion.
- Gout: A painful condition caused by uric acid crystal deposition in joints and tissues.
- Kidney Stones: Uric acid crystals may also accumulate in the kidneys, leading to stone formation.
Regulation and Treatment
- Low purine diet and medications like allopurinol (xanthine oxidase inhibitor) are used to control uric acid levels.
- Hydration and avoidance of alcohol and high-fructose foods help manage uric acid levels.
Thus, uric acid plays a critical role in purine metabolism and its mismanagement can lead to metabolic disorders.