Catalyzes the deamination of cytidine and deoxycytidine into uridine and deoxyuridine, respectively. May play an important role in testicular development and spermatogenesis. 2'-deoxycytidine + H(+) + H2O = 2'-deoxyuridine + NH4(+) cytidine + H(+) + H2O = NH4(+) + uridine Belongs to the cytidine and deoxycytidylate deaminase family.