Figure 1.

Inhibition of human IDO1 enzyme activity by β-lapachone. Dose-response assessment of increasing β-lapachone concentration on the activity of purified recombinant huIDO1. The assay was performed with 100 μM L-Trp substrate and the concentration of the product kynurenine was measured at 15 minutes while the enzyme was still active in the log phase. The data are plotted as percent inhibition of kynurenine production. The IC₅₀ of 440 nM was determined by nonlinear curve fitting.