FIGURE 6.
TR activity of TGRGCUG and TRGCUG analyzed at the hysteresis conditions for GR activity. A, the TR activities of untreated and glutathionylated TGRGCUG were compared using the Trx-coupled assay. B, the GR activities of untreated and glutathionylated TGRGCUG were compared at 100 μm GSSG. In both A and B the enzyme preparations were assayed at 1 nm TGR concentration and 150 μm NADPH. It should be noted that, to calculate the volume of enzyme preparation that ought to be used in the assay, glutathionylated TGR was assumed to be 2-fold diluted following desalting. This approximation could explain the slightly smaller slopes observed for this enzyme in both assays, as compared with the untreated one. C, the TR activity of TRGCUG was evaluated using the Trx-coupled assay both in the absence and presence of high concentration (1 mm) GSSG. The enzyme was assayed at 1 nm final concentration and 150 μm NADPH. The selenoenzyme (TGRGCUG and TRGCUG) concentrations considered were corrected according to their selenium contents.