ADSORPTION ACTIVITY AND CONFORMATION OF ALPHA-AMYLASE ON VARIOUS ULTRAFINE SILICA PARTICLES MODIFIED WITH POLYMER SILANE COUPLING AGENTS

Ultrafine silica particles were modified with various polymer-silane c oupling agents. Since the light scattering intensity of these particle s was low, the conformation of adsorbed enzyme can be evaluated by spe ctrophotometric methods, such as circular dichroism (CD). Adsorption i sotherms of Bacillus subtilis alpha-amylase and the activities of adso rbed alpha-amylase were measured under various adsorption conditions. Moreover, to discuss the extent of conformational changes upon adsorpt ion, the alpha-helix content of adsorbed alpha-amylase was elucidated from the CD spectrum measurements. The amount of adsorption was strong ly affected by the type of particles and increased with increasing sur face hydrophobicity. A stronger interaction at more-hydrophobic surfac es was found to cause larger conformational changes and to reduce the activity of adsorbed enzyme. Therefore, the surface properties have a large influence on the molecular states of enzymes on solid surfaces. However, in all the particles, the amount of adsorption decreased with increasing pH and decreasing temperature. Lower affinity between part icles and alpha-amylase at higher pH and/or lower temperature reduces the extent of conformational changes and increases the relative activi ty.