Performance evaluation of hyperbranched aramids as potential supports for protein immobilization

Several adducts of alpha-amylase and hyperbranched aramids have been evaluated in terms of their bioactivity performance. Twelve samples of hyperbranched aromatic polyamides, originated from either two AB(2)-type monomers or from five systems formed by reactant pairs (A(1) + B-3 Or A(3) + B-3 or A(2) + B-4) have been synthesized under different reaction conditions and used as protein supports. Through the addition of a suitable coupling agent, the enzyme fixation step has been carried out by joining the carboxylic groups on or near the outer surface of the aramids to the amino groups of the aminoacids present in alpha-amylase. A rather high efficiency of protein immobilization is observed in our aramids, their binding capability being almost an order of magnitude higher as compared to the commonly used insoluble supports. Each preparation of the immobilized enzyme is analyzed in terms of bioactivity retention as a function of time, as well as stability under various experimental conditions. Enzymatic activity has been evaluated both as k(m) (a measure of the enzyme affinity for the substrate) and as k(cat) (used for the determination of catalytic efficiency). Our data show that the linking of the enzyme to the polymeric support leads to the production of three different types of adducts with distinct enzymatic patterns. On the basis of our results it may be inferred that hyperbranched aramids are suitable supports for protein immobilization. The availability of these polymeric structures by simple synthetic preparations can open new perspectives for the development of finely tuned enzyme-based derivatives with pre-defined binding affinity, catalytic capability and structural stability, (C) 2000 Elsevier Science Ltd. All rights reserved.