FIGURE 2.

Influence of substrate concentration on the dephosphorylation of ³H-labeled dNTPs by SAMHD1. Upper row, incubations with 50 ng of mouse SAMHD1; lower row, incubations with 150 ng of human SAMHD1. Each enzyme was incubated in separate experiments with ³H-labeled dGTP, dATP, dTTP, or dCTP (200–6000 cpm/nmol) at the varying concentrations shown on the abscissa and with 20 μm effectors (color-coded in the graphs). Other incubation conditions, the quantitation of the deoxynucleosides formed during the reaction, and the calculation of K_m constants are described under “Experimental Procedures.” Ordinates indicate the nmol of deoxynucleoside (NdR) produced in 1 min by 1 mg of protein.