Fig. 2.

Electrochemical nanoconfinement experiments demonstrating that wild-type IDH1 activity is clearly observed using only IDH1-copurified NADP(H) (no NADP(H) was added). (A) Chronoamperogram showing IDH1 activity as increasing concentrations of DL-isocitrate are titrated into the solution. The injection concentrations shown are the final concentrations of each addition of isocitrate (not cumulative). (B) Cyclic voltammetry showing wild-type IDH1 activity at different concentrations of isocitrate. The gray trace shows IDH1 activity when 10 µM NADP⁺ was added to the solution. Conditions (A and B): (FNR+IDH1)@ITO/PGE electrode, temperature 25 °C, volume 4 mL, pH = 8 (100 mM HEPES, 10 mM MgCl₂), and enzyme loading ratios (molar): FNR/IDH1; 2/1. (A): electrode area 0.06 cm², 1,000 rpm, potential E (vs. standard hydrogen electrode, SHE) = +0.2 V. (B): 0.03 cm² electrode area, scan rate 1 mV/s, stationary electrode. Racemic DL-isocitrate was used for both A and B.