Electrooptical determination of the isoelectric point of globular proteins: Cytochrome c adsorbed on montmorillonite nanoplates

The purpose is to study the capability of the electric light scattering to determine the point of zero charge of native protein macromolecules adsorbed on colloid particles at low ionic strength and without using buffers. The chosen protein and particles are cytochrome c (cytC, globular haemoproteid) and montmorillonite (MM, negatively charged plate-like crystal). The pH-dependence of the electric polarizability gamma(pH) in the range pH 6-11 shows minimum which coincides with the isoelectric point determined by measuring the electrophoretic mobility mu(pH) of the cytC-MM particles.