This enzyme scavenges exogenous and endogenous cytidine and 2'-deoxycytidine for UMP synthesis. cytidine + H(+) + H2O = NH4(+) + uridine 2'-deoxycytidine + H(+) + H2O = 2'-deoxyuridine + NH4(+) Binds 1 zinc ion. Homodimer. Each monomer is composed of a small N-terminal alpha-helical domain and two larger core domains that have nearly identical tertiary structures and are related by approximate two-fold symmetry, but lack homology. Belongs to the cytidine and deoxycytidylate deaminase family.