Upper panel, transient kinetics for NTRC intramolecular electron transfer, after reduction by NADPH, as observed by stopped flow at 456 nm in the absence or presence of 2-Cys Prx or Trx x; kinetic traces of reoxidation could be adjusted to multiexponential fits, as indicated under “Results.” NTRC and NADPH concentrated samples were mixed to obtain final concentrations of 15 μm NTRC and 15 μm NADPH, in the absence or the presence of 50 μm 2-Cys Prx or Trx x, as indicated. For comparative purposes, a similar experiment was carried out with NTRCM. Lower panel, dependence on NADPH concentration of the kobs for the two reoxidation phases. NTRC reactions were followed by mixing 200-μl solutions of NTRC 15 μm with small volumes of concentrated NADPH solutions (0.09–0.3 mm). Other experimental conditions were as described in Fig. 2.