# Binding of Tetrachloroaurate(III) to Bovine or Human γ-Globulins

## TL;DR

This study explores how gold(III) interacts with γ-globulins in cow and human blood, revealing how it binds and affects protein structure.

## Contribution

The paper provides new insights into the binding stoichiometry and structural effects of gold(III) on γ-globulins using spectroscopic methods.

## Key findings

- 13 to 19 gold atoms bind per γ-globulin molecule depending on the solution and protein source.
- Gold(III) binding reduces β-sheet content in γ-globulins and increases disordered structures.
- Electrolyte concentration does not alter γ-globulin secondary structure as shown by CD spectra.

## Abstract

The interaction of metals with serum γ-globulins is of particular interest, as it can modulate immune system function and lead to unforeseen consequences following the intake of metal ions or their complexes, which are often considered (pro)drugs. This paper focuses on the interactions between gold(III) species and bovine or human serum γ-globulins in aqueous solutions. Using UV-Vis, fluorescence, and CD (circular dichroism) spectroscopy in diluted or 0.1 M NaCl aqueous solutions, we determined the most probable stoichiometry of the gold(III)-protein associates and their conditional binding constants. On average, 13 to 19 gold atoms bind per protein molecule, depending on the medium and protein origin, with apparent binding constants ranging from 3.6 to 4.6 (log K values; hydroxyl-containing complexes exhibit lower binding affinity). CD spectra revealed no changes in protein secondary structure induced by the increase in electrolyte concentration. However, the addition of gold(III) species resulted in a decrease in β-sheet content and a corresponding increase in turns or disordered fragments.