The effect of Indium Curcumin and Indium Diacetylcurcumin Complexes on Horseradish Peroxidase Enzyme

Curcumin, the active polyphenol component of the Curcuma longa plant has a wide range of biological activities including antioxidant, anti-inflammatory, antiproliferative, antibacterial and anticancer. Curcumin has a low aqueous solubility and poor stability and therefore it has low systemic bioavailability. Complexation of curcumin with metals improves its stability and bioavailability. Indium curcumin (In(cur)3) and indium diacetylcurcumin (In(DAC)3) was synthesized and characterized in 2005 by Mohammadi et al. Cytotoxicity and antioxidant potential of these complexes were evaluated on mouse lymphoma cells. The result showed that cytotoxicity and antioxidant activity of indium complexes was more than curcumin alone. In the previous investigation, we evaluated the effect of curcumin and it metal complexes on horseradish peroxidase (HRP) enzyme. Here, the effects of Indium curcumin (In(cur)3) and Indium diacetylcurcumin (In(DAC)3) was evaluated on kinetic parameters and oxidative stability of horseradish peroxidase enzyme. The results showed that the complexes increase activity of HRP remarkably. The complexes also enhance remaining activity of HRP at high concentrations of hydrogen peroxide indicating they increase oxidative stability of the enzyme. The complexes decrease affinity of HRP for hydrogen peroxide substrate and increase its affinity for phenol substrate. Activation energy of the enzyme reaction doesn’t change remarkably upon interaction of the enzyme with the complexes. The results of fluorescence spectroscopy implied that intensity of the emission increases after addition of the complexes to the protein solution probably due to an increase the distance between the tryptophan residue and the catalytic center. It can be concluded that In(cur)3 and In(DAC)3have a potential to improve activity of peroxidases and help them to eliminate excess hydrogen peroxide of the cells under normal and stress conditions.