Interaction between La 3+ and MP-11 in the physiological solution

Abstract

In this paper, the interaction between La 3+ and microperoxidase-11 (MP-11) in the imitated physiological solution was investigated with the electrochemical method, circular dichroism (CD) and ultraviolet–visible (UV–vis) absorption spectroscopy. It was found that the interaction ways between La 3+ and MP-11 are different with increasing the molar ratio of La 3+ and MP-11. When the molar ratio of La 3+ and MP-11 is less than 2, La 3+ mainly interacts with the metacetonic acid group of the heme group in the MP-11 molecules, causing the increase in the non-planarity of the porphyrin cycle in the heme group and the decrease in the content of the random coil conformation of MP-11. These structural changes would increase the exposure extent of the electrochemical active center of MP-11 and thus, La 3+ can promote the electrochemical reaction of MP-11 and its electrocatalytic activity for the reduction of H 2O 2 at the glassy carbon (GC) electrode. However, when the molar ratio of La 3+ and MP-11 is larger than 3, except binding to the carbonyl oxygen of the metacetonic acid group in the heme group, La 3+ interacts also with the oxygen-containing groups of the amides in the polypeptide chains of the MP-11 molecules, leading to the increase in the contents of the random coil conformation in the peptide of the MP-11 molecule, comparing with that for the molar ratio of less than 2. However, the non-planarity of the porphyrin cycle in the heme group is similar to that for the molar ratio of less than 2. Perhaps, the increase in the contents of the random coil conformation in the peptide of the MP-11 molecule would partially shield the electrochemical active center of MP-11 and is not favorable to the electrochemical and electrocatalytic reaction of MP-11. Thus, the reversibility of the electrochemical reaction of MP-11 and its electrocatalytic activity for the reduction of H 2O 2 are lower than that for the molar ratio of less than 2.