Smart biocatalysts: design and applications

Smart materials respond to chemical or physical changes in their environment in a predictable fashion. One class of such materials are smart polymers which can be used to design reversibly soluble-insoluble biocatalysts. One important advantage of such soluble polymer enzyme conjugates is in bioconversion of macromolecular or insoluble substrates. In addition, they share the advantage of reusability with conventional immobilized enzymes. Stimuli that are used to "recover" smart polymer - enzyme conjugates for reuse include changes in pH, temperature, ionic strength and addition of chemical species like calcium. In addition to these, enzymes linked to photoresponsive polymers have also been described in the literature. Both adsorption and covalent coupling have been used to create such polymer conjugates. End-group conjugation and site-specific conjugation are recently described strategies to obtain biocatalysts with better designs for solving mass transfer constraints. Some important applications of such smart biocatalysts are hydrolysis of starch, cellulose and proteins. Work has also been carried out on hydrolysis of pectins and xylans. All the above applications involve hydrolysis and are hence carried out in aqueous media. For synthetic applications such as synthesis of peptides, some photoresponsive polymers linked to proteases have recently been described.