Chymotrypsin Adsorption on Montmorillonite: Enzymatic Activity and Kinetic FTIR Structural Analysis

Area of Science:

• Biochemistry
• Soil Science
• Enzyme Kinetics

Background:

• Soils possess large surface areas and high adsorption capacities.
• Enzyme adsorption onto mineral surfaces can alter their activity.
• Understanding these interactions is crucial for soil science and biocatalysis.

Purpose of the Study:

• To investigate structural and solvation changes of alpha-chymotrypsin adsorbed on montmorillonite.
• To correlate these changes with alterations in enzyme activity.
• To elucidate the electrostatic basis of enzyme adsorption and its impact.

Main Methods:

• Transmission FTIR spectroscopy was used to study alpha-chymotrypsin.
• Enzyme adsorption on montmorillonite (a phyllosilicate) was analyzed.
• pH-dependent structural and activity changes were compared between solution and adsorbed states.

Main Results:

• Adsorption perturbed peripheral protein domains, causing minor secondary structure unfolding (15-20 peptide units).
• Inactivation in the pH range 5-7 was attributed to steric hindrance, not major structural changes.
• Specific amino/imino functions (His-40, -57, Ala-149) oriented towards the clay surface caused inactivation.
• Reversible activity recovery occurred when these functions lost their positive charge.

Conclusions:

• Enzyme inactivation upon adsorption to negatively charged clays is primarily due to steric hindrance of active site access.
• Structural changes are less significant than the orientation of charged residues near the catalytic cavity.
• This finding is relevant for applications involving enzyme adsorption and monitoring.