Conformational changes in protein molecules upon adsorption on ultrafine particles

Abstract

Conformational changes in hemoglobin (a “soft” protein) and catalase (a relatively “soft” protein) upon adsorption on ultrafine silica particles (average diameter 15 nm) have been studied by circular dichroism (CD). Because the light scattering intensity of the ultrafine silica particles is very low, the secondary structure of protein molecules on solid surfaces can be estimated from the CD spectra of the suspension of the ultrafine silica particles on which proteins are adsorbed. The extent of the changes in the secondary structure of both the protein molecules was found to increase with decreasing pH and adsorbed amount. Hemoglobin showed the changes in the secondary structure up to high pH and high adsorbed amount. Therefore, soft proteins are susceptible to conformational changes upon adsorption on solid surfaces. These CD spectrum data give us some quantitative information about the conformational changes in protein molecules upon adsorption on solid surfaces.