Comparison of Adsorption and Conformation of Hemoglobin and Myoglobin on Various Inorganic Ultrafine Particles.

Human hemoglobin and horse myoglobin were adsorbed on the two types of ultrafine silica (silica 1 and 2), titania, and zirconia particles under various conditions. The order of the affinity of the ultrafine particles to these proteins was silica 1 < silica 2 < zirconia = titania under the same adsorption condition. The conformational changes in these proteins upon adsorption and desorption were monitored by both circular dichroism and absorbance spectra. In both spectrum measurements, a similar tendency was observed, indicating that the adsorption of proteins causes the changes not only in the secondary structure but also in the tertiary structure. In all the particles, the extent of conformational changes upon adsorption increased with decreasing pH and adsorption amount. On the other hand, the extent of conformational changes was significantly affected by the particle type (its order was silica 1 < silica 2 < zirconia = titania) under the same adsorption condition. The percentage of desorption and the extent of refolding of desorbed proteins were lower when the extent of conformational changes in the adsorbed states was higher. These results clearly demonstrate that higher affinity between particle surfaces and proteins causes larger conformational changes and consequently leads to higher irreversibility in adsorption and conformational states.