Uridine diphosphate reductase of Ehrlich ascites tumor is insensitive to hydroxyurea

Uridine diphosphate (UDP) reductase was isolated in the supernatant fraction obtained after the acidification of the cytosol of Ehrlich ascites tumor cells, and was found insensitive to 10 mM hydroxyurea. However, cytidine diphosphate (CDP) reductase, being separated concurrently in the precipitate fraction, was readily inhibited. In the cytosol fraction of either Ehrlich ascites tumor, Yoshida ascites sarcoma or regenerating rat liver after partial hepatectomy, UDP reduction activity, in contrast to CDP reduction activity, is not sensitive to hydroxyurea.