Insight into the Mechanistic Basis of the Hysteretic-Like Kinetic Behavior of Thioredoxin-Glutathione Reductase (TGR)

Figure 2

Product inhibition patterns of T. crassiceps TGR by NADP⁺. Enzyme assays and incubation conditions were as described under Materials and Methods. (a) NADPH as the variable substrate at a constant GSSG concentration (70 μM) and the following fixed concentrations of NADP⁺: (○) 0; (●) 0.5 mM; (□) 1.5 mM; (■) 5 mM. Continuous lines were obtained from the corresponding double-reciprocal form of equation (3) using the parameters resulting from the global fitting of data. (b) GSSG as the variable substrate at a constant NADPH concentration (20 μM) and the following fixed concentrations of NADP⁺: (○) 0; (●) 0.8 mM; (Δ) 1.6 mM; (▲) 5 mM. Continuous lines were obtained from the corresponding double-reciprocal form of equation (4) using the parameters resulting from the global fitting of data. In all of these inhibition experiments, the final concentration of enzyme subunit was 6.1 nM. Each point represents mean ± standard deviation (n=6).

(a)

(b)