Binding of silver ions to alpha-lactalbumin

Abstract

The process and product of silver ions binding to alpha-lactalbumin (α-LA) were studied and discussed in this paper. The aim of the work was to explain the mechanism of reaction using interdisciplinary research. The kinetic study shows that binding equilibrium of silver to α-LA is achieved after 2 min. Process was fitted to pseudo-zero, zero and Weber-Morris models and can be distinguished by two distinct steps: firstly, graduate decline in silver concentration in solution and second step of silver concentration equilibration. The determined thermodynamic parameters showed that the reaction can occur spontaneously. Complementing the experiments, molecular dynamic simulations and DFT calculations have shown that aspartic and glutamic residues have the most significant contribution in the silver binding process. Spectroscopic (ATR-FT-IR and Raman) methods were used to compare structure of native protein and after binding of silver and they confirmed that the binding occurs with participation of acidic residues of protein. Morphology and information about surface of particles were determined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) (with energy dispersive X-ray spectroscopy - EDX). Such experiments have shown that silver forms nearly homogeneous metallic structure onto protein. Silver has shown to be released from complexes in synthetic intestine physiological fluids in the highest quantity in stomach with comparison to mimicked intestine system. Cytotoxicity study showed better biocompatibility and bioavailability of composite than control.