Chiral discrimination of 2'-deoxy-L-cytidine and L-nucleotides by mouse deoxycytidine kinase: low stereospecificities for substrates and effectors.

The effects of four kinds of 2'-deoxy-L-nucleoside 5'-triphosphates and L-ATP, which are enantiomers of natural D-dNTPs and D-ATP, on deoxycytidine kinase (dCK) partially purified from mouse leukemic P388 cells were investigated. Only L-dCTP did not act as a phosphate donor while other L-dNTPs and L-ATP showed 15-30% of the activity of the corresponding D-dNTP or D-ATP. L-dCTP inhibited dCK non-competitively with 2'-deoxycytidine (D-dCyd) and competitively with phosphate donor D-ATP. These inhibitory effects of L-dCTP on dCK were similar to the results of earlier studies using D-dCTP. Thus, L-dCTP was shown to be capable of serving as a feedback inhibitor for dCK instead of D-dCTP. Mouse dCK was also able to phosphorylate L-dCyd, as demonstrated in the case of human dCK. The present results suggest that the chirality of not only dCyd as the substrate but also nucleotides as the substrate or effector is not strictly discriminated by dCK.