Manipulation of the bioactivity of glucose oxidase via raft-controlled surface modification

In this article, poly[poly(ethyleneglycol) acrylate] (polyPEG-A) with mercaptothiazoline ester terminal group was synthesized directly by reversible addition fragmentation chain transfer (RAFT) polymerization using a mercaptothiazoline ester functional RAFT agent. The functional polyPEG-A was then conjugated to glucose oxidase (GOx) via surface-tethered amino groups through covalent amide coupling. Sorensenformaltitration assay revealed that GOx retained ∼14 free amino groups available for covalent modification. The conjugation reaction turned out to be efficient and mild. Colorimetric method was applied to evaluate the enzymatic activity of native GOx and its derivatives by introducing another enzyme, horseradish peroxidase. The modified GOx with polymeric chains exhibited reduced enzymatic activity toward the catalytical oxidation of glucose, but with significantly increased thermal stability and elongated lifetime. When GOx was modified with polyPEG-A [molecular weight (MW), 45,000; polydispersity index, 1.12] the enzymatic activity was decreased to 37 U/mg, only 29% left. However, when incubated at 25 °C the modified GOx still retained 9.6% of its original bioactivity after 60 days, whereas the native GOx only lived for 29 days. The more polymer chains or the longer polymer chain attached, the more reduction of the enzymatic activity resulted, however, the longer the lifetime of the enzyme obtained.