Fig. 7.
Redox state dependence of heme dissociation from IDO1. IDO1 (1.1 µM) was incubated for 40 min at 37 °C in the presence of 10 µM 2. Heme dissociation from IDO1 was tracked by the loss of absorbance at the IDO1 λmax of the Soret peak: 404 nm for ferric IDO1 and 425 nm for ferrous IDO1. (A) Spectra of ferric IDO1 at various times. Inset shows a comparison of the loss in absorbance for both ferric and ferrous IDO1 as a function of time. (B) Spectra of ferrous IDO1 at various times. IDO1 was reduced using 5 mM sodium dithionite in a nitrogen-flushed sealed cuvette, and the decay of dithionite can be seen by its decreasing absorption below 375 nm. Inset is a scheme showing inhibitor binding to IDO1 in place of heme, causing the observed reduction in absorbance.