Involved in nucleoside degradation. Phosphorylates cytidine to CMP. Can also act on deoxycytidine and uridine, but is most active with cytidine. ATP is the most preferred phosphate donor, but it can also use GTP, CTP or UTP. ATP + cytidine = ADP + CMP + H(+) Mg(2+) is the preferred cation, followed by Mn(2+) and Co(2+). kcat is 280 sec(-1) with cytidine as substrate. kcat is 226 sec(-1) with deoxycytidine as substrate. kcat is 222 sec(-1) with ATP as substrate. High levels of activity within a broad pH range of 5.0-9.0. Optimum temperature is 90 degrees Celsius. Belongs to the carbohydrate kinase PfkB family.