KINETIC MECHANISM AND END-PRODUCT REGULATION OF DEOXYGUANOSINE KINASEFROM BEEF-LIVER MITOCHONDRIA

Initial-rate kinetic measurements with the affinity purified 8-deoxygu anosine (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 K-m, for dGuo was 4.7 mu M, and that fo r ATP was 780 mu M. One product, dGMP, was competitive with both subst rates, while the other, ADP, was competitive with ATP and non-competit ive with dGuo. Qualitatively identical results were obtained with an a lternative substrate, dTTP, and with alternative product inhibitors, d IMP and dTDP. These results are consistent with a random Bi Bi kinetic mechanism, judging from the formation of a dead-end complex of the en zyme, dGuo and ADP, dGTP competes very strongly with ATP (K-1 = 0.03 m u M), but is non-competitive towards dGuo. The more weakly-bound dGDP is competitive with both substrates.