Figure 3

Stability of assay buffers. Redox potentials [mV] (open squares) and pH values (filled circles) were measured for the indicated time intervals. A two-buffer system of citric acid and sodium phosphate was used to adjust the desired pH values while the redox values were adjusted by the addition of L-cysteine. Timepoint [t = 0] reflects the initially adjusted value; the setpoint of the redox potential is given as dashed line. Redox values above the setpoint are considered more oxidizing, whereas changes towards the negative potential are more reducing. Buffers representative for the extracellular space, i.e. mimicking an oxidizing (-150 mV) and neutral (pH 7.2) compartment, were measured in the absence (A) or presence (B) of the substrate Tg. Buffers mimicking the endosomal compartment were characterized by reducing (-220 mV) and slightly acidic (pH 6.0) conditions (C). Buffers representing the lysosomes displayed the same reducing redox-conditions as endosomes (c.f. C), but were more acidic (pH 5.0) (D). Values are given as mean +/- SD.