Chymotrypsin Adsorption on Montmorillonite: Enzymatic Activity and Kinetic FTIR Structural Analysis
1999
Baron, M.H., H | Revault, M. | Servagent-Noinville, S. | Abadie, J. | Quiquampoix, H. | Laboratoire de Dynamique Interactions et Réactivité (LADIR) ; Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut de Chimie - CNRS Chimie (INC-CNRS)-Centre National de la Recherche Scientifique (CNRS) | École nationale vétérinaire, agroalimentaire et de l'alimentation Nantes-Atlantique (ONIRIS) | Ecologie fonctionnelle et biogéochimie des sols et des agro-écosystèmes (UMR Eco&Sols) ; Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Institut de Recherche pour le Développement (IRD)-Institut National de la Recherche Agronomique (INRA)-Centre international d'études supérieures en sciences agronomiques (Montpellier SupAgro)-Institut national d’études supérieures agronomiques de Montpellier (Montpellier SupAgro)
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Show more [+] Less [-]English. Soils have a large solid surface area and high adsorptive capacities. To determine if structural and solvation changes induced by adsorption on clays are related to changes in enzyme activity, ␣-chymotrypsin adsorbed on a phyllosilicate with an electroneg-ative surface (montmorillonite) has been studied by transmission FTIR spectroscopy. A comparison of the pH-dependent structural changes for the solution and adsorbed states probes the electro-static origin of the adsorption. In the pD range 4.5-10, adsorption only perturbs some peripheral domains of the protein compared to the solution. Secondary structure unfolding affects about 15-20 peptide units. Parts of these domains become hydrated and others entail some self-association. However, the inactivation of the catalytic activity of the adsorbed enzyme in the 5-7 pD range is due less to these structural changes than to steric hindrance when three essential imino/amino functions, located close to the entrance of the catalytic cavity (His-40 and-57 residues and Ala-149 end chain residue), are oriented toward the negatively charged mineral surface. When these functions lose their positive charge, the orientation of the adsorbed enzyme is changed and an activity similar to that in solution at equivalent pH is recovered. This result is of fundamental interest in all fields of research where enzymatic activity is monitored using reversible adsorption procedures.
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