Pyrimidine-nucleoside phosphorylase () is an enzyme that catalyzes several phosphorolysis reactions which convert a pyrimidine nucleoside into the corresponding pyrimidine, by cleavage of the α-D-ribose 1-phosphate sugar unit:Boyer, P.D., Lardy, H. and Myrback, K. (Eds.), The Enzymes, 2nd ed., vol. 5, Academic Press, New York, 1961, p. 237-255.
a pyrimidine nucleoside + phosphate (Pi) α-D-ribose 1-phosphate + a pyrimidine base
For example, uridine gives uracil:
The reaction is reversible, so this is also how the pyrimidine nucleosides uridine, cytidine, 2'-deoxyuridine, and thymidine can be made in the bacterium Bacillus stearothermophilus in which the enzyme was characterised. It has also been described from Enterobacter aerogenes.
This enzyme belongs to the family of glycosyltransferases, specifically the pentosyltransferases. The systematic name of this enzyme class is pyrimidine-nucleoside:phosphate alpha-D-ribosyltransferase. This enzyme is also called Py-NPase.
Structural studies As of late 2007, two structures have been solved for this class of enzymes, with PDB accession codes and .
References