Ž . Journal of Molecular Catalysis B: Enzymatic 8 2000 233–244 www.elsevier.comrlocatermolcatb Characterization of the activity of penicillin G acylase immobilized onto nylon membranes grafted with different acrylic monomers by means of g-radiation M.S. Mohy Eldin a,1 , U. Bencivenga a , S. Rossi a , P. Canciglia a,2 , F.S. Gaeta a , J. Tramper c , D.G. Mita a,b, ) a International Institute of Genetics and Biophysics, CNR, Via G. Marconi, 12, 80125 Naples, Italy b Department of Human Physiology and Integrated Biological Functions, II UniÕersity of Naples, Via S.M. di Costantinopoli, 16, 80138 Naples, Italy c Department of Food Technology and Nutritional Sciences, Wageningen Agricultural UniÕersity, P.O. Box 8129, 6700 EV Wageningen, Netherlands Received 12 March 1999; accepted 17 May 1999 Abstract Ž . Ž . Penicillin G acylase PGA has been immobilized onto nylon membranes grafted with methylmethacrylate MMA or Ž . Ž . diethyleneglycoldimethacrylate DGDA monomers by means of g-radiation. Hexamethylenediamine HMDA has been Ž . used as spacer between the grafted membranes and the enzyme. Glutaraldehyde GA was used as crosslinking to couple the enzyme to the HMDA. The catalytic membranes so prepared were studied as a function of pH and temperature of the solution containing the substrate. The membranes showing the best characteristics were the ones grafted with DGDA. The dependence of the behavior of these membranes on several experimental conditions was studied, i.e., the temperature and duration of the aminoalkylation process, spacer concentration, the glutaraldehyde concentration and the enzyme concentra- tion. The experimental conditions giving the best performance of the catalytic membranes have been deduced. The time requested to obtain 50% of substrate conversion, i.e., hydrolysis of cephalexin, has been studied as a function of its initial concentration. q 2000 Elsevier Science B.V. All rights reserved. Keywords: Immobilized enzymes; Biocatalytic membranes; Penicillin G acylase; g-Radiation; Cephalexin 1. Introduction The production of valuable compounds in the chemical, pharmaceutical and food industries ) Corresponding author. Telefax: q 0039-81-2395887; E-mail: mita@iigbna.iigb.na.cnr.it 1 Permanent address: Department of Polymers and Pigments, National Research Center, Dokki, Cairo, Egypt. 2 Permanent address: Department of Physiology, University of Messina, Salita Sperone, 36 Messina, Italy. benefits from the use of enzymes as biocata- lysts. The advantages in using immobilized en- zymes promoted the exploitation of catalytic membranes in industrial processes, notwith- standing that the immobilized biocatalyst wx 1 exhibited lower activity than that of an equivalent amount of the free form. This was essentially due to the interactions between the macromolecule and the supporting matrix. The knowledge of these interactions became relevant 1381-1177r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S1381-1177 99 00061-2