Fig. 3.

H₂S binds with low micromolar affinity and slowly reduces the DosS heme iron. (A) Representative changes to the UV–Visible spectra of DosS(Fe³⁺) (3 μM) resulting from the addition of different concentrations of Na₂S, relative to DosS without Na₂S. Inset shows a substrate saturation curve of H₂S binding to DosS(Fe³⁺) generated using UV–Vis absorption data points obtained from the titration DosS with increasing concentrations of Na₂S. UV–Vis spectra are representative of at least 3 independent assays. (B) Representative UV–Visible spectra of recombinant DosS(Fe³⁺) (3 μM) (λ_max = 407 nm, blue curve) 90 min after the addition of 30 μM CO (λ_max = 407 nm, orange curve), 30 μM Na₂S (λ_max = 410 nm, red curve), CO + Na₂S (λ_max = 414 nm, green curve), or Na₂S + CO+0.5 mM DTH (λ_max = 418 nm, magenta curve). Inset shows absorption spectra replotted to highlight the α (570 nm) and β (535 nm) peaks. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)