Activation of poly(dimer acid-co-alkyl polyamine) particles for covalent immobilization of a-amylase Nesrin Hasirci a, * , Serpil Aksoy b , Hayrettin Tumturk b a Department of Chemistry, Faculty of Arts and Sciences, Middle East Technical University, Ankara 06531, Turkey b Department of Chemistry, Gazi University, Ankara 06500, Turkey Received 29 July 2005; received in revised form 8 May 2006; accepted 8 May 2006 Available online 27 June 2006 Abstract Poly(dimer acid-co-alkyl polyamine) particles were activated by using various chemicals such as carbodiimide (CDI), ethylene diamine (EDA), and hexamethylene diamine (HMDA) and studied as support materials for covalent immobili- zation of a-amylase. The activities of the immobilized enzymes on these activated particles were investigated. The highest activity of free enzyme was obtained at pH 7.5 while this value was shifted to pH 6.5 for CDI and EDA activated systems and to pH 8.0 for HMDA activated system. The highest activities of immobilized enzymes were obtained at higher tem- perature (55 °C) than that of the free enzyme (40 °C). Kinetic parameters were calculated as 2.51, 3.13, 3.47 and 3.17 g dm À3 for K m and 1.67 · 10 À3 , 6.16 · 10 À4 , 7.34 · 10 À4 and 3.30 · 10 À4 g dm À3 min À1 for V max for the free enzyme, and CDI, EDA and HMDA activated immobilized systems, respectively. Enzyme activities were found to be about 75.0%, 62.5% and 95.0% of the original, for CDI, EDA and HMDA activated systems, respectively, after one month of storage while free enzyme lost its activity completely in 20 days. In repeated batch experiments, after 40 uses in 3 days; 91.3%, 77.6% and 99.1% of the original enzyme activities were retained by CDI, EDA and HMDA activated systems, respectively. Among the systems prepared, HMDA activated poly(dimer acid-co-alkyl polyamine) particles demonstrated the highest stability and efficient reusability for the immobilized a-amylase. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Enzyme immobilization; a-Amylase; Poly(dimer acid-co-alkyl polyamine); Ethylene diamine; Hexamethylene diamine 1. Introduction Stabilization of enzymes upon immobilization is a very important technique for their potential contin- uous or repeated use in the industrial applications especially for biotechnology, biomedicine and food technology areas. Advantages of immobilization include reusability, enhanced stability and rapid sep- aration of the enzyme from the reaction medium. Immobilization can be achieved by various methods such as entrapment, microencapsulation, copoly- merization, crosslinking, physical adsorption, chem- ical attachment and covalent binding. Covalent binding of enzymes on solid supports has some advantages such as increased thermal and storage stability, prevention of the leakage and decreased diffusion problems for the substrates and products in the reaction medium. Immobilization is often 1381-5148/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.reactfunctpolym.2006.05.004 * Corresponding author. Tel.: +90 312 2103193; fax: +90 312 2103200. E-mail address: nhasirci@metu.edu.tr (N. Hasirci). Reactive & Functional Polymers 66 (2006) 1546–1551 www.elsevier.com/locate/react REACTIVE & FUNCTIONAL POLYMERS