Hyperbranched polymer conjugated lipase with enhanced activity and stability

Hyperbranched aromatic polyamides were synthesized from p-phenylenediamine and trimesic acid, and subjected to the conjugation of lipase using carbodiimide as a coupling reagent. The molecular weights of the conjugates were determined by size exclusion chromatography and gel electrophoresis, which showed that each polymer molecule could be covalently modified with a maximum of five to six lipase molecules. The K. of the conjugate to substrate, p-nitrophenylpalmitate, was equal to native lipase while V-max was increased by 20%, suggesting an enhanced structural transition of lipase during catalysis conducted at the periphery of the polymer. Moreover, the conjugate exhibited a significantly enhanced stability at high temperature or in the presence of organic solvent, as compared to its native counterpart. This might due to the hydrophilic carboxylic groups of polymer that created a suitable microenvironment for lipase. These results indicate that hyperbranched polymer-enzyme conjugate, with the enhanced activity and stability, is promising for industrial biocatalysis. (c) 2007 Published by Elsevier B.V.