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⚗️biological chemistry ii review

Purine nucleoside phosphorylase (pnp)

Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025

Definition

Purine nucleoside phosphorylase (pnp) is an enzyme that catalyzes the conversion of purine nucleosides into their corresponding purine bases and ribose-1-phosphate. This process plays a vital role in purine metabolism, specifically in the catabolism of nucleotides, allowing for the recycling of purines and the maintenance of cellular nucleotide levels.

5 Must Know Facts For Your Next Test

  1. Pnp is crucial for the salvage pathway of purine metabolism, which recycles purines from degraded nucleic acids.
  2. Deficiency in pnp can lead to immunodeficiency diseases due to the accumulation of toxic metabolites.
  3. The enzyme exhibits specificity for purine nucleosides such as adenosine and guanosine but does not act on pyrimidine nucleosides.
  4. Pnp functions by utilizing inorganic phosphate to cleave the glycosidic bond between the sugar and the nitrogenous base.
  5. Inhibitors of pnp have potential therapeutic applications, especially in cancer treatment, by disrupting nucleotide metabolism.

Review Questions

  • How does purine nucleoside phosphorylase contribute to the recycling of purines in cellular metabolism?
    • Purine nucleoside phosphorylase plays a key role in the salvage pathway by breaking down purine nucleosides into free purine bases and ribose-1-phosphate. This recycling process ensures that cells can efficiently reuse purines rather than relying solely on de novo synthesis, which is energy-intensive. By converting nucleosides back into bases, pnp helps maintain adequate levels of nucleotides necessary for various cellular functions.
  • Discuss the potential consequences of a deficiency in purine nucleoside phosphorylase on human health.
    • A deficiency in purine nucleoside phosphorylase can lead to severe immunodeficiency diseases, primarily due to the accumulation of toxic metabolites such as deoxyadenosine. This buildup can inhibit normal lymphocyte development and function, resulting in increased susceptibility to infections and certain types of cancer. The lack of functional pnp disrupts the balance of nucleotide metabolism, highlighting its critical role in maintaining immune health.
  • Evaluate the significance of purine nucleoside phosphorylase in cancer treatment strategies focusing on nucleotide metabolism.
    • Purine nucleoside phosphorylase is significant in cancer treatment because it represents a target for therapeutic intervention aimed at disrupting nucleotide metabolism in rapidly dividing cancer cells. Inhibitors of pnp can lead to an imbalance in nucleotide pools, potentially hindering DNA and RNA synthesis required for tumor growth. This strategic targeting offers a promising avenue for developing novel anticancer therapies, especially considering the reliance of cancer cells on altered metabolic pathways for survival and proliferation.