Uridine phosphorylase

Uridine phosphorylase is an enzyme that plays a crucial role in the metabolism of nucleotides. It is responsible for the breakdown of uridine into uracil and ribose-1-phosphate. This enzyme is found in various organisms, including bacteria, plants, and animals. In humans, uridine phosphorylase is encoded by the UP gene.

Function

Uridine phosphorylase is an essential enzyme in the salvage pathway of nucleotide metabolism. It catalyzes the reversible phosphorolysis of uridine, resulting in the release of uracil and ribose-1-phosphate. This reaction allows the recycling of uridine and the generation of ribose-1-phosphate, which can be utilized in the synthesis of nucleotides.

Structure

Uridine phosphorylase is a homodimeric enzyme, meaning it consists of two identical subunits. Each subunit contains a catalytic site responsible for the enzymatic activity. The active site of uridine phosphorylase contains a conserved histidine residue that acts as a nucleophile during the phosphorolysis reaction.

Role in Nucleotide Metabolism

Uridine phosphorylase is involved in the metabolism of pyrimidine nucleotides. It is responsible for the breakdown of uridine, a pyrimidine nucleoside, into uracil and ribose-1-phosphate. The released uracil can be further metabolized to produce other pyrimidine nucleotides, while ribose-1-phosphate can be utilized in the synthesis of nucleotides or other cellular processes.

Clinical Significance

Uridine phosphorylase has been implicated in various diseases and conditions. For example, deficiencies in this enzyme have been associated with hereditary pyrimidine nucleoside phosphorylase (PNP) deficiency, a rare autosomal recessive disorder characterized by immunodeficiency, neurologic abnormalities, and developmental delay. Additionally, uridine phosphorylase has been explored as a potential target for cancer therapy, as its inhibition can lead to the accumulation of toxic nucleoside analogs in cancer cells.

See Also

• Nucleotide metabolism
• Pyrimidine nucleotides
• Enzyme kinetics