Inhibition mechanism of lanthanum ion on the activity of horseradish peroxidase in vitro

In order to understand the inhibition mechanism of lanthanum ion (La3+) on the activity of horseradish peroxidase (HRP), the effects of La3+ on the activity, electron transfer and conformation of HRP in vitro were investigated by using cyclic voltammetry (CV), atomic force microscopy (AFM), circular dichroism (CD), high performance liquid chromatography (HPLC), matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI-TOF/MS) and inductively coupled plasma mass spectrometry (ICP-MS). It was found that La3+ can combine with the amide groups of the polypeptide chain in HRP molecule, forming the complex of La3+ and HRP (La-HRP). The formation of the La-HRP complex causes the destruction of the native structure of HRP molecule, leading to the decrease in the non-planarity of the porphyrin ring in the heme group of HRP molecule, and then in the exposure extent of active center, Fe(III) of the porphyrin ring of HRP molecule. Thus, the direct electrochemical and catalytic activities of HRP are decreased. It is a possible inhibition mechanism of La3+ on the activity of peroxidase.