SAXS and SEM Studies of Supramolecular Aggregation of Enzymes on Carbon Adsorbent Surfaces and the Effect of this Process on the Biocatalytic Properties of Immobilized Lipase

The distribution character and supramolecular aggregation of the enzyme - recombinant lipase (rec-Lip) on the surfaces of carbon adsorbents, such as multiwalled carbon nanotubes (MWCNTs) and pyrocarbon supports (Sibunit^TM, activated carbon) are examined by small angle X-ray scattering (SAXS) and scanning electron microscopy (SEM) techniques. The SAXS studies show that rec-Lip molecules aggregate on the carbon surface with the formation of nanoparticles with sizes from 4 nm (monomers) to 26 nm (aggregates of more than 10 molecules). SEM images demonstrate that not only single round nanoparticles with a size more than 20 nm but also complex branched aggregates formed by short fibrils of single nanoparticles are observed on the surface. It is revealed that the enzyme activity of biocatalysts prepared by rec-Lip adsorption on carbon supports has the minimum value if the enzyme is in the monomeric form. Information about the distribution character of the immobilized enzyme on the adsorbent surfaces and about its supramolecular aggregation is not only of the fundamental value for heterogeneous biocatalysis, but are also of scientific and practical value because these processes govern the properties of biocatalysts, primarily, their enzyme activity.