Protection of Enzymes Against Heat Inactivation by Enzyme-Polymer Conjugates

Along with the quick advancements in enzyme technology, inactivation has emerged as the key barrier for enzymes to be fully utilized as biocatalysts. Here, a novel strategy is presented for the preservation of the enzymatic activity even after heat treatment by grafting enzymes onto the thermal responsive block copolymer via an activated ester-amine reaction. A new water-soluble activated ester monomer, acrylic polyethylene glycol (PEG) functionalized 3-fluoro-4-hydroxybenzoate is synthesized. This activated ester monomer and 2-methoxyethoxyethyl methacrylate (MEEMA) as copolymer monomers are first used to synthesize water-soluble polymers bearing activated ester for post-polymerization modification with amines. Two model enzymes containing amine residues, urease, and papain, are grafted onto the resulting thermal responsive polymers to obtain PMEEMA-co-Enzyme, respectively. The obtained particles of polymer-enzyme conjugates flocculate above the low critical solution temperature (LCST) and redissolve when cooled below that temperature. The activity of the conjugated enzymes has been studied after high temperatures treatment and compared to that of free enzymes. The enzymatic activity assays show that the thermosensitive polymer can act as a stabilizer under high-temperature conditions after multipoint grafting with the enzyme, thus protecting the enzyme from thermal inactivation.