Inhibition of calf thymus DNA polymerase-alpha by deoxyribonucleoside triphosphates.

Kinetic evaluation of DNA polymerase-α (DNA nucleotidyltransferase, EC [2.7.7.7][1].) was conducted using the enzyme purified from calf thymus and obtained from a commercial source. At saturating levels of template, the reaction was first order with respect to dTTP and, at optimum dTTP, was first order with respect to homopolymer template. At subsaturating levels of template, however, the reaction yielded nonhyperbolic kinetics which were consistent with substrate inhibition by dTTP. This substrate inhibition was competitive with template and independent of Mg2+ concentration. The noncomplementary nucleotides, dCTP, dGTP, and dATP, all inhibited the reaction in a noncompetitive manner with respect to dTTP and in a competitive manner with respect to template. Noncomplementary homopolymer as well as pyrophosphate also inhibited the reaction competitive with template. This study suggests that the deoxyribonucleoside triphosphate precursors of DNA may regulate the replication of cellular DNA through substrate inhibition of DNA polymerase-α. [1]: pending:yes