Study of the physicochemical interactions between Thermomyces lanuginosus lipase and silica-based supports and their correlation with the biochemical activity of the biocatalysts

Abstract

The interactions between Thermomyces lanuginosus lipase (TLL) and phenyl silica-based supports affect the immobilization mechanisms and their catalytic behavior. The modulation of phenyl groups density on the silica surface and porous characteristics were determined by TGA, FTIR, 29Si NMR and N2 adsorption porosimetry. The correlation of the affinity constant and maximum adsorption capacity with the lixiviation results allowed determine differences in the enzyme adsorption mechanism in function of the immobilization pH and phenyl groups density. In the support with low phenyl groups density, the adsorption of a higher amount of enzyme is promoted. However, the pore confinement and the microenvironment generate decrease expressed activity. This can be due to the stiffness and structural changes of the adsorbed enzymes, which were studied by following the thermal stability at 65°C, protein distribution, kinetic parameters and diffusion restrictions. The biocatalyst prepared on support with low density of phenyl groups at pH6.0, exhibits the best balance between expressed activity, thermal stability and immobilization efficiency. This due to homogeneous distribution of the enzyme in the support with phenyl groups, which increases the affinity of the enzyme by the substrate, even the diffusion restrictions decrease the Vmax. These results contribute to rationalize the effects of the immobilization conditions and supports type on its catalytic behavior.