Inhibition mechanism of Tb(III) on horseradish peroxidase activity

The inhibition mechanism of Tb(III) on horseradish peroxidase (HRP) in vitro was discussed. The results from MALDI-TOF/MS and X-ray photoelectron spectroscopy (XPS) showed that Tb(III) mainly interacts with the O-containing groups of the amides in the polypeptide chains of the HRP molecules and forms the complex of Tb(III)-HRP, and, in the complex, the molar ratio Tb(III)/HRP is 2 : 1. The results from CD and atomic force microscopy (AFM) indicated that the coordination effect between Tb(III) and HRP can lead to the conformation change in the HRP molecule, in which the contents of alpha-helix and beta-sheet conformation in the peptide of the HRP molecules is decreased, and the content of the random coil conformation is increased. Meanwhile, the coordination effect also leads to the decrease in the content of inter- and intrapeptide-chain H-bonds in the HRP molecules, resulting in the HRP molecular looseness and/or aggregation. Thus, the conformation change in the HRP molecules can significantly decrease the electrochemical reaction of HRP and its electrocatalytic activity for the reduction of H2O2.