Hydrolase with a preference for pyrimidine substrates. Has high activity with 5-methyl-dCTP, and much lower activity with CTP, dCTP, 5-hydroxy-dCTP, 2-hydroxy-dATP and 8-hydroxy-dGTP. CTP + H2O = CMP + diphosphate + H(+) dCTP + H2O = dCMP + diphosphate + H(+) Divalent metal ions. Mg(2+) or Mn(2+). Optimum pH is 8.5-9. Monomer. Belongs to the Nudix hydrolase family.