Modulation of antioxidant enzyme by light and heavy rare earth metals: A case study with catalase

The present study highlights the hazardous effect of heavy and light rare earth elements (REEs) on bovine liver catalase (BLC) using a combination of spectroscopic and computational methods. The presence of Praseodymium chloride (PrCl₃) and Gadolinium chloride (GdCl₃) resulted in a substantial reduction in catalytic efficiency of BLC by approximately 1.8 and 2.6 fold, respectively. The compromised activity was further accompanied by conformational rearrangements at the secondary and tertiary levels as evidenced by circular dichroism (CD) and fluorescence spectroscopy. These analyses revealed a significant decrease in α-helical content and a simultaneous increase in random coils, disrupting intramolecular hydrogen bonding. Furthermore, the zeta potential (ζ) of BLC demonstrated a reversal from negative to positive ζ values upon the addition of PrCl₃ and GdCl₃, indicating BLC-lanthanide complex formation. Isothermal titration calorimetry (ITC) supports spontaneous interaction with negative free energy favouring endothermic reaction. This was further supported by docking studies which revealed the binding of PrCl₃ and GdCl₃ within the active site of BLC thus interfering with the catalytic ability to degrade hydrogen peroxide (H₂O₂). Nevertheless, a significant decline in the melting temperature (T_m) of BLC was observed in the presence of lanthanides suggesting the thermal instability of the enzyme. Thus, a similar approach could be applied to evaluate the hazardous effects of lanthanides on structural and functional changes in other proteins or similar biomolecules.