Complexometric titrations of protein-bound metal ions: a method for determining binding constants

Area of Science:

• Biochemistry and Biophysical Chemistry
• Analytical Chemistry
• Metalloprotein Studies

Background:

• Understanding protein-metal ion interactions is crucial for biological function and disease.
• Accurate quantification of binding affinity and stoichiometry is essential for characterizing metalloproteins.
• Existing methods may have limitations in scope or applicability.

Purpose of the Study:

• To develop and validate a novel electrochemical method for quantifying protein-metal ion interactions.
• To determine both the binding constants and stoichiometry of metal ions bound to proteins.
• To assess the applicability of this method to biologically relevant metalloproteins.

Main Methods:

• Development of an electrochemical titration technique.
• Titration of protein-bound metal ions with complexometric reagents.
• Electrochemical monitoring of changes in free metal ion concentration.

Main Results:

• The method successfully quantifies protein-metal ion binding affinity and stoichiometry.
• Demonstrated applicability to Cu(II) and Ag(I) binding to bovine cuprozinc superoxide dismutase apoprotein.
• Identified limitations related to the relative affinities of the protein and complexometric reagent.

Conclusions:

• A robust electrochemical method for studying protein-metal ion interactions has been established.
• This technique provides valuable insights into the binding characteristics of metalloproteins.
• The method offers a new tool for biochemical and biophysical investigations of metal ion coordination in proteins.