Pyrimidine nucleotidases from human erythrocyte possess phosphotransferase activities specific for pyrimidine nucleotides

Abstract
Two cytoplasmic forms of pyrimidine nucleotidase (PN‐I and PN‐II) have been purified from human erythrocytes to apparent homogeneity and partially characterized. They preferentially hydrolyse pyrimidine 5′‐monophosphates and 3′‐monophosphates respectively. PN‐I and PN‐II operate as interconverting activities, capable of transferring the phosphate from the pyrimidine nucleoside monophosphate donor(s) to various nucleoside acceptors, including important drugs like 3′‐azido‐3′‐deoxy‐thymidine (AZT), cytosine‐β‐d‐arabinofuranoside (AraC) and 5‐fluoro‐2′‐deoxy‐uridine (5FdUrd), pyrimidine analogues widely used in chemotherapy. Kinetic analysis showed linear behaviour for both PN‐I and PN‐II. PN‐I phosphotransferase activity revealed higher affinity for oxy‐nucleosides with respect to deoxy‐nucleosides, whereas the contrary seems to be true for PN‐II. These results show for the first time that soluble pyrimidine nucleotidases are endowed with pyrimidine‐specific phosphotransferase activity.

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