FIGURE 7.

Cytoplasmic sulfur trafficking during sulfur globule oxidation in A. vinosum. A, summary of sulfur transfer reactions detected in vitro. The cysteines responsible for sulfur binding are depicted. B, model of sulfur transfer reactions occurring in vivo. Rhd_2599 and TusA are introduced as sulfur-donating proteins for the Dsr system. Thiol groups and persulfides are shown in the ionized or protonated state according to their supposed pK_a values of around 8.5 (46) and 6.2 (47), respectively. Because persulfides are 1–2 pK_a units more acidic than their thiol equivalents, we calculated the pK_a of the assumed carrier molecule glutathione amide persulfide on the basis of the pK_a for glutathione (48) to be ∼7.2. DsrC-Cys-111 and Cys-100 correspond to Cys_A and Cys_B, respectively (9). See “Discussion” for detailed explanation.