DNA deaminase (cytidine deaminase) which may act as an inhibitor of retrovirus replication and retrotransposon mobility via deaminase-dependent and -independent mechanisms. a 2'-deoxycytidine in single-stranded DNA + H(+) + H2O = a 2'-deoxyuridine in single-stranded DNA + NH4(+) APOBEC3H from old world monkeys has retained its antiviral activity, while it is lost in other primates. Belongs to the cytidine and deoxycytidylate deaminase family.