Amperometric Analysis of the Effect of Heavy Metals on the Activity of Isocitric Dehydrogenase

Abstract

The effect of heavy metals on the enzyme isocitrate dehydrogenase (ICDH) was measured by amperometrically monitoring the reduction of the coenzyme NADP⁺ on a three electrode system based on screen‐printing technology. The working electrode was fabricated using rhodinized carbon to facilitate the NADP⁺ conversion at an operating potential of +300 mV vs. Ag/AgCl compared with >+700 mV for bare carbon electrodes. The enzyme inactivation by mercury(II) was linear over the range 20–250 µg L⁻¹, with a detection limit of 10 µg L⁻¹. The limits of detection achieved for other inactivating metals tested were in the low mg L⁻¹ range [(6.4 mg L⁻¹ for Pb(II), 0.09 mg L⁻¹ for Cd(II), and 0.05 mg L⁻¹ for Cu(II))]. Zn(II) was found to produce a slight activation on ICDH at concentrations below 250 µg L⁻¹, higher values yielded inactivation of the enzyme activity. The same effect was also observed for Ca(II), which only produced inhibition at concentrations above 1 mg L⁻¹. Mg(II) can also be determined with a limit of detection of 50 µg L⁻¹ based on the activation effect it has on the enzyme. The developed amperometric assay was suitable for the activity measurement of the enzyme ICDH and was therefore applied to the screening of metals in polluted water and soil samples. However, the inhibition/activation effect of different metals on the enzyme indicates the difficulty of using this enzyme for metal screening.

Keywords:

• Metal ion inhibition/activation
• NADPH
• Isocitrate dehydrogenase
• Soil analysis