Deoxycytidine kinase is an enzyme catalyzing the phosphorylation of deoxycytidine in nucleotide salvage biosythesis. It will also phosphorylate deoxyadenosine and deoxyguanosine when these compounds are present at higher concentrations. Deoxycytidine kinase is inhibited by dCTP. Unlike thymidine kinase, whose activity fluctuates over the course of the cell cycle, the activity of deoxycytidine kinase stays relatively constant.