Adsorption of cytochrome c on montmorillonite nanoplates: Protein concentration dependence

Cytochrome c [cytC] is a mitochondrial hemoprotein functioning as electron carrier in the respiratory chain of the biological cells. Being adsorbed on colloid particles cytC can be introduced in the cells by phagocytoses. In the present work we study the adsorption of cytC on montmorillonite (MM) particles combining the electro-optic and electrophoretic techniques. MM particles were chosen as nanoplates having negative pH-independent charge and high ratio surface/mass. The measurements were done at pH 6.5 where cytC globule is positively charged. The main employed method is the electric light scattering based on orientation of colloid particles in sinusoidal electric field. Interfacial electric polarizability was obtained from the degree of orientation at steady-state and the particle size - from the relaxation time after the field switching off. Microelectrophoresis was used to monitor the alteration of the surface charge at protein adsorption. The cytC-concentration dependence of the polarizability and the mobility shows out that the total (net) charge of cytC-MM complex turns its sign from negative to positive, the isoelectric point appears at 5:3 mg/mg (0.135 mol/kg) cytC/MM and saturated protein adsorption is reached at additional twofold increasing of cytC/MM ratio. The suspension is stable at low and high protein concentrations, at intermediate ones aggregation arises. (C) 2015 Elsevier Inc. All rights reserved.