LIN HUANG
Department of Chemical and Biomolecular Engineering, National University of Singapore

Abstract

UCST-type polymer-immobilized enzymes use lower temperatures for biocatalyst separation than for homogeneously biocatalytic reactions, so as to ensure prevention of the immobilized enzymes from deactivation as well as achieving high biocatalytic performance. This article highlights the developments of nano-sized UCST-type polymer-immobilized enzymes in biocatalysis. The characteristics of the reported nano-sized UCST-type polymer-immobilized enzymes and their advantages and disadvantages in terms of biocatalytic performance, separation and reusability are summarized with an outlook on the engineering of enzymes with UCST-type polymers for biocatalysis.

INTRODUCTION
Immobilization of enzymes to polymers has become a research hotspot to empower enzymes with more extraordinary properties and broader usage. As compared with free enzymes, polymer-immobilized enzymes can improve operational and thermal stabilities in harsh environments such as extreme pH, concentration and temperature. Polymers possess underlying stimulus-responsive features, which allows them to undergo a conformational change or coil-to-globule transition upon a change in external stimuli such as temperature, counterion, pH, electricity and light (1-5).

Amid stimulus-responsive polymers, thermoresponsive polymers have been extensively studied in academic and applied polymer sciences over the last decades (2-8). A thermoresponsive polymer undergoes a change in solubility in a polymer-solvent system with varying temperature (9,10). As the temperature increases, the polymer dissolves in the solvent through an upper critical solution temperature (UCST) process, and/or precipitates from the solution through a lower critical solution temperature process. In Scheme 1 is shown the representative phase diagram pattern of UCST- ...