Performance evaluation of hyperbranched aramids as potential supports for protein immobilization

Several adducts of alpha-amylase and hyperbranched aramids have been evalua ted in terms of their bioactivity performance. Twelve samples of hyperbranc hed 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, th e enzyme fixation step has been carried out by joining the carboxylic group s on or near the outer surface of the aramids to the amino groups of the am inoacids present in alpha-amylase. A rather high efficiency of protein immobilization is observed in our arami ds, their binding capability being almost an order of magnitude higher as c ompared to the commonly used insoluble supports. Each preparation of the im mobilized enzyme is analyzed in terms of bioactivity retention as a functio n of time, as well as stability under various experimental conditions. Enzy matic activity has been evaluated both as k(m) (a measure of the enzyme aff inity for the substrate) and as k(cat) (used for the determination of catal ytic efficiency). Our data show that the linking of the enzyme to the polym eric support leads to the production of three different types of adducts wi th distinct enzymatic patterns. On the basis of our results it may be infer red that hyperbranched aramids are suitable supports for protein immobiliza tion. The availability of these polymeric structures by simple synthetic pr eparations can open new perspectives for the development of finely tuned en zyme-based derivatives with pre-defined binding affinity, catalytic capabil ity and structural stability, (C) 2000 Elsevier Science Ltd. All rights res erved.