Expression of pyrimidine 5 '-nucleotidase subclass I during erythrocyte maturation in rats

The subclass I enzyme of rat pyrimidine 5'-nucleotidase (P5N-I), which pref erentially hydrolyzes (deoxy) CMP and UMP, is distributed specifically in r ed blood cells (RBCs), and its activity increases approximately six-fold as compared to the control value after erythropoietic induction by phenylhydr azine administration. In this study, we detected rat P5N-I protein by using antibodies against the chicken P5N-I enzyme. The molecular mass of rat P5N -I was approximately 37 kDa, as estimated by gel filtration chromatography and Western blot analysis. The pI value of the enzyme was approximately 5.7 . This protein band was detected only in RBC lysate extract, i.e., not in c ytosol from the erythropoietic spleen. Protein mass of the P5N-I enzyme, es timated by immunoblot analysis, was increased in proportion to the enzyme a ctivity after erythropoietic induction in rats. No phosphorylation of the e nzyme protein was detected by immunoblot analysis with anti-phosphoserine o r anti-phosphotyrosine antibody. In conclusion, these findings indicate tha t the rat P5N-I enzyme is expressed specifically in reticulocytes and may t herefore be essential in the maturation process of rat erythrocytes.