Enhanced Activity of Pyrimidine 5′-Nucleotidase in Rat Red Blood Cells during Erythropoiesis

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Abstract
A nucleotidase that catalyzed selective hydrolysis of pyrimidine 5'-nucleotides was investigated in rat red blood cells (RBCs). The enzyme had similar catalytic properties to human pyrimidine 5'-nucleotidase I (P5N-I). The P5N-I deficiency was known to be closely correlated with the human inherited disease, non-spherocytic hemolytic anemia. Similar to the human P5N-I, the rat enzyme preferentially hydrolyzed 5'-(d)CMP and 5'-UMP but no reactivity was observed with any 3'-nucleotide. Molecular mass of the enzyme was estimated to be approximately 38 kDa by gel filtration and SDS-polyacrylamide gel electrophoresis. Another subclass of pyrimidine 5'-nucleotidase, P5N-II, was also present in rat RBCs. This P5N-II-like enzyme, which resembled a 5'(3')-nucleotidase, preferentially hydrolyzed both 5'- and 3'- of (d)TMP or (d)UMP, but no cytosine nucleotide was hydrolyzed by the enzyme. Results from the reactivity with the antibody against rat 5'(3')-nucleotidase and estimated subunit molecular mass of the enzymes, about 26 kDa, suggested that the P5N-II-like enzyme had a similar structure to the 5'(3')-nucleotidase. The P5N-I-like activity in rat RBCs increased 5 to 6-fold at 4 days after phenylhydrazine injection, and reached a maximum at 6 to 7 days. No change in the activity of P5N-II-like nucleotidase was observed during the experimental period. The increase in rat P5N-I activity coincided with maturation of the erythrocytes.