FIGURE 4.

Interaction of Fe^III-Hb with sulfide at low sulfide to heme ratios. A, concentrations of sulfane sulfur and thiosulfate formed after 30 min of incubation of Fe^III-Hb (100 μm heme) in aerobic 100 mm HEPES buffer, pH 7.4, with 100 or 200 μm Na₂S at 25 °C. The data represent the mean ± S.D. (error bars) of 3–4 independent experiments. B, representative spectral changes observed upon incubation of Fe^III-Hb (10 μm heme) with Na₂S (10 μm) under the same conditions as in A. The blue spectrum is of Fe^III-Hb, and the black and red spectra were recorded at 20 min and 24 h, respectively, after the addition of Na₂S.