Titrations of [4Fe-4S] ScNsrR with NO.
A, absorbance spectra of [4Fe-4S] NsrR following sequential additions of NO up to a [NO]:[FeS] ratio of 10.5 (black lines show spectra recorded at ratios of 0, 2.1, 6.3, and 10.5). B, fluorescence spectra obtained during a titration equivalent to that in A; inset shows changes in more detail. Black lines show spectra recorded at [NO]:[FeS] ratios of 0 (lower) and 3.8 (upper). C and D, CD spectra obtained during a titration equivalent to that in A. Black lines show spectra recorded at [NO]:[FeS] ratios of 0 and 2.2 in C, and 2.2 and 6.2 in D. Arrows indicate the direction of intensity changes. ScNsrR (28 μm) was in 20 mm Tris, 20 mm MES, 20 mm Bistris propane, 100 mm NaCl, 250 μm GSH, 5% (v/v) glycerol, pH 8.0.