Kinetic mechanism and end-product regulation of deoxyguanosine kinase from beef liver mitochondria.

Initial-rate kinetic measurements with the affinity purified 2-deoxyguanosine (dGuo) kinase from beef liver mitochondria yielded reciprocal plots which converged on the abscissa, with either dGuo or ATP as the varied substrate. The limiting Km for dGuo was 4.7 microM, and that for ATP was 780 microM. One product, dGMP, was competitive with both substrates, while the other, ADP, was competitive with ATP and non-competitive with dGuo. Qualitatively identical results were obtained with an alternative substrate, dTTP, and with alternative product inhibitors, dIMP and dTDP. These results are consistent with a random Bi Bi kinetic mechanism, judging from the formation of a dead-end complex of the enzyme, dGuo and ADP. dGTP competes very strongly with ATP (Ki = 0.03 microM), but is non-competitive towards dGuo. The more weakly-bound dGDP is competitive with both substrates.