FIGURE 9.

Characterization of the active site cysteine adducts formed by TsdA variants. The indicated TsdA variants (A–D) were either left untreated (Native), incubated with equimolar thiosulfate for 3 min in 100 mm ammonium acetate, pH 4.25, or incubated with 50 mm tetrathionate for 1 h in 30 mm Tris-HCl, pH 8.0, 160 mm NaCl. Samples were quenched with 0.1% TFA and analyzed by ESI-MS. Note that the tetrathionate-treated samples contain a duplicated series of peaks at masses 340 Da greater than those of the primary set of peaks arising from proteins in complex with a tetrathionate molecule.