text: Wild-type enzymes and variants of << CDA >> (Lys27Gln and Ala70Thr) and DCK (Ile24Val, Ala119Gly, and Pro122Ser) were expressed in and purified from Escherichia coli, and enzyme kinetic parameters were estimated for cytarabine (Ara-C), dFdC, and its metabolite [[ 2',2'-difluorodeoxyuridine ]] (dFdU) as substrates.