High stabilization of immobilized Rhizomucor miehei lipase by additional coating with hydrophilic crosslinked polymers: Poly-allylamine/Aldehyde-dextran

Immobilized enzymes have a very large surface region which is not in contact with the support surface and, thus, have potential as a target for novel stabilization strategies. In this paper, coating the surfaces of such enzymes with a highly hydrophilic and compact cross-linked poly-aminated polymer as a strategy to increase the thermal stability of the immobilized enzymes is proposed. In particular, Rhizomucor miehei lipase (RML) was immobilized by interfacial adsorption onto octyl-agarose and further coated with poly-allylamine (PAA), a polymer that is very rich in primary amino groups. Cross-linking of the PAA layer to coat the immobilized enzyme was carried out, in situ, by reaction with freshly oxidized dextran (aldehyde-dextran). The PAA layer only exerted moderate stabilizing effects (around 4-fold), but further cross-linking with aldehyde-dextran highly increased the stabilizing effects; the new derivative was 440-fold more stable than uncoated derivative at 55 degrees C and pH 7 and exhibited 6-fold more catalytic activity compared to the soluble enzyme used for immobilization. We hypothesize that the hydrophilicity of PAA reduces the exposure of internal hydrophobic pockets to the enzyme surface at high temperatures. Besides, the compactness of the polymer may reduce distortion of the enzyme surface during inactivation.