Conformation and stability of three different enzymes adsorbed onto SiO2 nanoparticles

In this study, SiO2 nanoparticles (nano-SiO2, 20nm) and SiO2 microparticles (micro-SiO2, 150µm) were chosen as carriers for three different enzymes: α-Amylase, papain and trypsin to investigate the effect of particle size on the properties of adsorbed enzymes. The adsorbed amount on 100mg SiO2 particles for α-Amylase, papain and trypsin under their optimum adsorption conditions were 70.93%, 92.26% and 82.61%, respectively. The studies performed on enzyme activity pointed out that both nano-SiO2 and micro-SiO2 could greatly improve the pH and thermal stability of enzymes in strongly denaturing environments, and nano-SiO2 were superior to micro-ones. After the treatment of 90 °C for 1h, the relative activity of nano-adsorbed α-Amylase, papain and trypsin had increased by 10.2%, 17.6% and 69.1% compared with their native states under similar conditions, respectively. The results of the surface hydrophobicity of the adsorbed enzymes revealed that enzymes underwent structural changes when they were attached on silica particles of various diameters. Generally, more unfolding was observed for enzyme adsorbed on micro-SiO2 compared with that adsorbed on nano-ones under otherwise similar conditions, and the fraction of activity lost correlated well with the unfolding content of attachment proteins.