Preparation and Properties in Organic Solvents of Noncovalent PEG-Enzyme Complexes

Abstract

It is well established that enzymes can be advantageously employed in organic solvents. In fact, there are an enormous number of applications in organic synthesis and numerous examples also in the fields of food-related conversions and analysis. However, enzymes show a lower catalytic efficiency (up to three or four orders of magnitude) when employed in organic solvents rather than in aqueous buffer. It is evident that such behavior represents an obstacle to exploit at industrial level the advantages which come from using enzymes in organic solvents (,). One of the reasons that could be responsible for the lower catalytic activity of enzymes in organic solvents can be ascribed to diffusional limitations (). Generally, when enzymes are employed in organic solvents, they are used as a suspended powder and the dispersion degree of the powder may represent a critical factor for the expression of the catalytic activity. In fact, the activity shown by an enzyme depends on the number of productive encounters that occur between the enzyme molecule and the substrate. Consequently, all methods that may increase the dispersion of the enzyme in organic solvents may be of interest in improving biocatalyst performance in nonaqueous media. Therefore, those methods that allow the dissolution of the enzyme in the organic solvent deserve particular attention because they represent a way to fully disperse the enzyme in the reaction system. Several procedures such as enzyme complexation with ion-pair forming surfactants () or synthetic amphipatic lipids that coat the enzyme molecule () or covalent linking of the protein to amphipatic polymers such as poly(ethylene glycol) (PEG) () have been described. Here, we report on a methodology suitable to prepare subtilisin