Figure 4.

Kinetic characterization of S. aureus SQR. (A) Wild-type (WT) SQR exhibits sulfide:quinone oxidoreductase activity with the sulfide substrate (Na₂S), while C167S and C344S SQRs exhibit no activity. The duroquinone turnover is plotted as a function of Na₂S concentration for WT SQR (○), C167S SQR (□), and C344S SQR (◇). The dashed lines through empty circles, empty squares, and empty diamonds are fits to the Michaelis–Menten equation (see Table 2). (B) SQR and CstB catalyze the production of thiosulfate from the sulfide substrate (Na₂S), with no activity observed with the C167S and C344S SQRs. Thiosulfate turnover is plotted as a function of concentration of Na₂S for WT SQR (○), C167S SQR (□), and C344S SQR (◇). The dashed lines through the empty circles, empty squares, and empty diamonds are fits to the Michaelis–Menten equation (see Table 2).