Figure 4.

Thermodynamic parameters of hemithioacetal formation. A, extinction coefficients for GSH-MGO and NAC-MGO at 288 nm in PBS were determined in the presence of 50 mm thiols to shift equilibrium toward product formation. B, 4 mm MGO in PBS was incubated with the indicated amounts of GSH at 37 °C to determine the concentration of the resulting hemithioacetal. Nonlinear curve fitting was performed as described in supporting methods and produced an excellent fit for the experimental data (red line), yielding an equilibrium constant of 510 m⁻¹. C, calculated values of free MGO expressed in mm (left axis, black line) or as percentage of total MGO (right axis, blue line) are shown as a function of the concentration of GSH and MGO present in equal amounts. Values on the x axis show the concentrations per reactant (e.g. 5 mm reactants corresponds to 5 mm GSH + 5 mm MGO).