FIGURE 6.

Formation of red IscS in vitro. A, purified wild-type IscS (100 μm) was incubated with l-alanine (100 mm) and Na₂S (100 mm) in the presence of Tris (120 mm (pH 8.0)) at room temperature. The UV-visible absorption spectra were taken at 0, 1 min, 1 h, 2 h, 3 h, and 4 h. Inset, a photograph of IscS proteins before (1) and after (2) incubation with l-alanine and Na₂S at room temperature for 3 h. B, l-alanine is essential for formation of red IscS in vitro. Purified wild-type IscS (100 μm) was incubated with buffer (spectrum 1), l-alanine (100 mm, spectrum 2), d-alanine (100 mm, spectrum 3), or glycine (100 mm, spectrum 4) in the presence of Na₂S (100 mm) and Tris (120 mm (pH 8.0)) at room temperature. Spectra were taken after incubation at room temperature for 3 h.