Figure 8.

Resonance Raman spectra of Fe^III-Ngb treated with sulfide. High-energy region of the spectra monitoring the time-dependent changes in Fe^III-Ngb (400 μm) in 100 mm HEPES buffer, pH 7.4, containing 20% glycerol (v/v) incubated with Na₂S (10 mm) at 25 °C under aerobic. The data were obtained using 413.1-nm excitation with 10–25-milliwatt laser power. Measurements for each sample took ∼10 min (various exposure time and accumulations). Initially, the observed ν₂, ν₃₈, ν₃, and ν₄ vibrations at 1580, 1549, 1507, and 1375 cm⁻¹, respectively, represent a 6-coordinate ferric low-spin heme. With time, the appearance of the ν₃ and ν₄ vibrational frequencies at 1482 and 1362 cm⁻¹, respectively, indicates a 6-coordinate ferrous low-spin heme.