Recycles cytidine and 2-deoxycytidine for uridine and 2-deoxyuridine synthesis, respectively. Catalyzes the hydrolytic deamination of cytidine and 2-deoxycytidine to form, respectively, uridine and 2-deoxyuridine. cytidine + H(+) + H2O = NH4(+) + uridine 2'-deoxycytidine + H(+) + H2O = 2'-deoxyuridine + NH4(+) Binds 1 Zn(2+) ion per subunit. kcat is 4.8 and 3.5 sec(-1) with cytidine and 2-deoxycytidine as substrate, respectively. Homotetramer. Belongs to the cytidine and deoxycytidylate deaminase family.