Rat spleen cytoplasmic nucleotidase: characterization and its physiological significance.

1. A cytoplasmic nucleotidase, which preferably hydrolyzed 5'-dUMP, was investigated in rat spleen. 2. Total activity of the nucleotidase increased about 3-fold in the spleen of anemic rat was caused by phenylhydrazine administration. This increase was repressed by the injection of methotrexate, an inhibitor of DNA synthesis. 3. Activities of heme oxygenase or acid phosphatase did not correlate to the change of the nucleotidase activity. 4. The nucleotidase catalyzed dephosphorylation of 3'(5')-dUMP, 3'(5')-dTMP and 3'-UMP more readily, in the presence of Mg2+. Its optimum pH was around 6.0-6.5. It was stimulated by the addition of deoxyinosine. 5. These catalytic properties and tissue distribution of the enzyme, abundant in the thymus, spleen and intestine, were similar to that of 5'(3')-nucleotidase in rat liver [Fritzson P. (1978) Adv. Enzym. Regul. 16, 43-61]. 6. A possible physiological significance of the nucleotidase is in reutilization of preformed pyrimidine nucleotides.