pyrimidine nucleoside salvage

Definition

Target type: biologicalprocess

Any process that generates a pyrimidine nucleoside, one of a family of organic molecules consisting of a pyrimidine base covalently bonded to a sugar ribose, from derivatives of it, without de novo synthesis. [GOC:jl]

Pyrimidine nucleoside salvage is a crucial metabolic pathway that allows cells to recycle and reuse pre-existing pyrimidine bases and nucleosides, ensuring a continuous supply of these essential building blocks for DNA and RNA synthesis. This process bypasses the de novo synthesis pathway, which is more energy-intensive and requires a greater number of enzymatic steps.

The salvage pathway primarily involves two key enzymes: **uridine phosphorylase (UP) and thymidine phosphorylase (TP)**.

1. **Uridine Phosphorylase (UP):** UP catalyzes the reversible phosphorolysis of uridine, converting it to uracil and ribose 1-phosphate. This reaction can also proceed in the reverse direction, allowing for the synthesis of uridine from uracil and ribose 1-phosphate.

2. **Thymidine Phosphorylase (TP):** TP similarly catalyzes the reversible phosphorolysis of thymidine, yielding thymine and deoxyribose 1-phosphate. This reaction can also be reversed to synthesize thymidine.

**The salvage pathway for pyrimidine nucleosides can be broadly divided into two branches:**

* **Uracil Salvage:** Uracil, obtained from the degradation of RNA or DNA, is salvaged via UP, which converts it to uridine. Uridine is then phosphorylated by uridine kinase to uridine monophosphate (UMP), which serves as a precursor for other pyrimidine nucleotides.

* **Thymine Salvage:** Thymine, another product of DNA degradation, is salvaged through TP, which converts it to thymidine. Thymidine is then phosphorylated by thymidine kinase to thymidine monophosphate (TMP), which can be incorporated into DNA.

**Other Enzymes Involved in the Salvage Pathway:**

* **Deoxycytidine Kinase (dCK):** dCK phosphorylates deoxycytidine to deoxycytidine monophosphate (dCMP), which can be further converted to dCTP, a precursor for DNA synthesis.

* **Cytidine Deaminase:** This enzyme catalyzes the deamination of cytidine to uridine, thereby linking the salvage pathways of cytosine and uracil.

**Importance of Pyrimidine Nucleoside Salvage:**

* **Efficient Utilization of Precursors:** The salvage pathway allows cells to recycle and reuse pre-existing pyrimidine bases and nucleosides, saving energy and resources.

* **Maintaining Nucleotide Pools:** This pathway ensures a constant supply of pyrimidine nucleotides for DNA and RNA synthesis, particularly during periods of rapid cell growth and division.

* **Preventing Accumulation of Toxic Metabolites:** By salvaging pyrimidine bases, the pathway prevents their accumulation, which can be detrimental to cellular functions.

* **Target for Therapeutic Intervention:** Disrupting the pyrimidine nucleoside salvage pathway has shown promise in cancer therapy, as it can inhibit tumor cell proliferation.
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Proteins (2)

Compounds (5)