Figure 5.

Inhibition of the G. intestinalis thymidine kinase activity with dTTP.A, enzyme activity measured with 200 μM thymidine as the substrate in the presence of different dNTPs at 200 μM. B, enzyme activity with 25 μM and 50 μM thymidine and variable concentrations of dTTP as the inhibitor. The curves in (B) were fitted by nonlinear regression to the inhibitor versus response (three parameters) function in GraphPad Prism 9.3.1 (IC₅₀ = 30 ± 3 μM and R² = 0.99 for the 25 μM series; IC₅₀ = 43 ± 1 μM and R² = 0.96 for the 50 μM series). The graphs in (A) and (B) represent the average of three independent experiments with standard errors, except for the 50 μM series in (B) (n = 2).