Study on the interaction behavior of lysozyme with lanthanide ions by flow injection chemiluminescence analysis

Abstract

The interaction behavior of lysozyme with trivalent lanthanide ions (Ln^III) was investigated by flow injection chemiluminescence (FI-CL) analysis. It was found that lysozyme with Ln^III could form a 1 : 1 association complex that remarkably quenched CL intensity from the luminol–lysozyme reaction, and the quantitative correlation equation of CL intensity decrements versus the logarithm of the concentration of Ln^III ΔI = A ln C_Ln + B was established. The results showed the sensitive factor A varied as atomic number Z increased monotonically, and A_LL of light lanthanides (LL) from La^III to Eu^III was less than A_HL of heavy lanthanides (HL) from Gd^III to Lu^III. The relationships of A vs. Z plot for LL and HL with a Gd^III break at f⁷ were clearly presented, and the correlations of A with physical parameters (γ_±, ΔH_hyd and E^o) of Ln^III were discussed. Using a homemade FI-CL model, the binding constants (K = 10⁵ to 10⁶ level) and binding sites (n = 1.0) were obtained, and the binding affinity abilities increased with increasing Z along the Ln^III series. The thermodynamic parameters of lysozyme with Ln^III were obtained, and the results showed that the reaction was a spontaneous process by electrostatic interaction. The possible mechanism and application of the luminol–lysozyme–Ln^III CL system were given.