Abstract
A new strategy to increase the enzyme-loading capacity of porous supports was investigated. Lipase from Pseudomonas fluorescens (PFL) was immobilized on octyl-agarose (OA) beads and treated with polyethyleneimine (PEI). Then, PFL was immobilized on the previous PFL layer. Next, the biocatalyst was coated with PEI and a third layer of PFL was added. Sodium dodecyl sulfate polyacrylamide electrophoresis showed that the amount of PFL proportionally increased with each enzyme layer; however, the effects on biocatalyst activity were not as clear. Hydrolyzing 50 mM of triacetin at 25 degrees C, the activity of the three-layer biocatalyst was even lower than that of the bi-layer one; on the contrary its activity was higher when the activity was measured at 4 degrees C in the presence of 30% acetonitrile (that reduced the activity and thus the relevance of the substrate diffusion limitations). That is, the advantage of the multilayer formation depends on the specific activity of the enzyme and on the diffusion limitations of the substrate. When octyl agarose (OA)-PFL-PEI-PFL preparation was treated with glutaraldehyde, the activity was reduced, although the enzyme stability increased and the immobilization of the last PFL layer offered results similar to the one obtained using the three-layer preparation without glutaraldehyde modification (90%).