Figure 9. Specific activity for wild-type and mutant forms of E. coli RNR in the presence of different substrate/effector pairs.
Wild-type is shown in black, Gln294Ala in grey, and Arg298Ala in white. Activity was measured by a coupled assay that follows nicotinamide adenine dinucleotide phosphate (NAPDH ) consumption (see Materials and methods) for the following substrate and effector concentrations: 1 mM CDP and 3 mM ATP (far left), 1 mM CDP and 175 μM dATP (second to left), 1 mM ADP and 120 μM dGTP, 1 mM GDP and 250 μM TTP, and 1 mM CDP/UDP and 1 μM dATP (far right). Since dATP at high concentrations (175 μM) inhibits the enzyme, the sets of bars at the far left represent control experiments to show activity levels under active (CDP/ATP) and inactive (CDP/dATP) conditions.