Adsorption and binding of protein on “clean” (homoionic) and “dirty” (coated with Fe oxyhydroxides) montmorillonite, illite and kaolinite

• Published in: Soil biology & biochemistry 1989, Vol.21 (7), p.911-920
• Main Authors: Fusi, P., Ristori, G.G., Calamai, L., Stotzky, G.
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Biological and medical sciences; Chemical, physicochemical, biochemical and biological properties; Fundamental and applied biological sciences. Psychology; Organic matter; Physics, chemistry, biochemistry and biology of agricultural and forest soils; Soil science
• ISSN: 0038-0717; 1879-3428
• DOI: 10.1016/0038-0717(89)90080-1

The adsorption and binding of two proteins, catalase (CA) and β-lactoglobulin (LG) on clay minerals (montmorillonite, illite and kaolinite) homoionic to Ca 2+ (ldclean” clays) or coated with two types of polymeric oxyhydroxides of Fe(III) (“dirty” clays) were studied. Equilibrium adsorption isotherms were generally of type L (Langmuir). The shapes of the adsorption isotherms for the Ca-clays and the corresponding dirty clays were similar, except for CA adsorbed on Ca-montmorillonite coated with polymeric Fe(OH) 3 (prepared from Fe(NO 3) 3 at pH 2.2). CA and LG intercalated some montmorillonite systems. The shapes of the binding isotherms of CA and LG were similar to those of the equilibrium adsorption isotherms, and the retention of relatively large amounts of protein after washing reflected a strong affinity of these proteins for the clays. Adsorption and binding of proteins occurred in all systems, regardless whether the pH b of the clay suspensions was above or below the isoelectric point of the proteins. The higher external surface area of the dirty clays than of the clean clays did not significantly increase the amounts of CA and LG adsorbed, indicating that the proteins did not penetrate the spaces between the spheres or rods of the polyhydroxides of Fe on the surface of the clays, i.r. Spectra of the protein-clay complexes showed some shifts in the vibration bands of the CO and N—H groups of peptide bonds, suggesting that slight perturbations in protein conformation occurred as a consequence of their adsorption on the clays.