Figure 4.

Inhibition of sGC activity by PPi. The PPi inhibition was measured for the basal (A), SNP-stimulated (B), and YC-1-activated (C) human sGC. The activity was measured at various concentrations of PPi and GTP. The data are represented as Dixon plot (1/velocity vs. concentration of the inhibitor). The K_i for PPi was determined as the projection to the abscissa at the intersection point of the plots. The replotting of the data as 1/velocity vs. 1/[GTP]. (Insets) Indicated competitive type of inhibition by PPi. The concentrations of PPi are indicated for each plot (μM). The plots are representative of three independent measurements for both α^Nβ and α^Cβ enzymes with similar results. The plotted data are means of triplicate value ± SD. Some error bars fall within the symbols.