Fig. 4. Comparison of the reduction of insulin catalyzed by MaTrxs.

(A) DTT-dependent activity: 9 µM MaTrx2 (triangles), 3 µM MaTrx6ΔSp (squares), and 6 µM MaTrx7 (diamonds) were added to 0.33 mM DTT and 0.13 mM insulin in 100 mM KPO₄ pH 6.8 under anaerobic conditions. The complete reaction without the addition of thioredoxin was included as a negative control (circles). Absorbance at 650 nm at 2 min intervals is shown. The data are the mean ± SD of triplicate reactions and the specific activity (ΔA650/min² × 10⁻³/mg) of each thioredoxin is shown in the inset. (B) Lipoamide-dependent activity: 12 µM MaTrx2 (triangles), 3 µM MaTrx6ΔSp (squares), and 6 µM MaTrx7 (diamonds) were added to 0.33 mM NADH, 4 units lipoamide dehydrogenase, 0.05 mM lipoamide and 0.13 mM insulin in 100 mM KPO₄ pH 6.8 under anaerobic conditions. The complete reaction without the addition of thioredoxin was included as a negative control (circles). Absorbance at 650 nm at 4 min intervals is shown. The data are the mean ± SD of triplicate reactions and the specific activity (ΔA650/min² × 10⁻³/mg) of thioredoxin is shown in the inset.