Adsorption of a-amylase onto poly(acrylamide/maleic acid) hydrogels H. TuÈmtuÈrk a , T. C ° aykara a , M. S ° en b, *, O. GuÈven b a Department of Chemistry Faculty of Arts and Science, Gazi University, 06500 Ankara, Turkey b Hacettepe University, Department of Chemistry, 06532 Beytepe, Ankara, Turkey Abstract Poly(acrylamide/maleic acid) [P(AAm/MA)] hydrogels were prepared by irradiating the ternary mixtures of AAm/ MA and water by g rays at ambient temperature. The in¯uence of the MA on the adsorption of a-amylase, optimum working conditions and storage stability of enzyme were investigated. The adsorption capacity of hydrogels were found to increase from 0.40 to 0.71 mg a-amylase/g dry gel with increasing amount of MA in the gel system. Maximum enzyme activities were observed at lower pH values and higher temperatures for adsorbed enzyme compared with free enzyme. Kinetic parameters were calculated as 2.51 g/dm 3 for K m and 1.67 Â 10 À3 g/dm 3 min for V max for free enzyme and in the range of 12.3±12.9 g/dm 3 for K m and 1.63 Â 10 À3 ±1.96 Â 10 À3 g/dm 3 min for V max depending on the amount of MA in the hydrogel. While, the enzymatic activity of free enzyme was completely lost after 20 days, adsorbed enzyme retained 47±59% of its original activity after 20 days, depending on the amount of MA in the hydrogels. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: Hydrogel; Poly(acrylamide/maleic acid); Adsorption; a-Amylase 1. Introduction The possibilities of using various polymeric and copolymeric matrices for immobilization of enzymes have been widely described in the literature. General operational advantages of immobilized enzymes are reusability, possibility of batch or continuos oper- ational modes, rapid termination of reactions, con- trolled product formation and easy separation of the product, great variety of engineering design for con- tinuous process and possible greater eciency in con- secutive multistep reactions. Amylase belongs to an enzyme group, very commonly used in food and fer- mentation industry. There have been many studies on the immobilization of a-amylase used for the hydroly- sis of starch and production of maltose. Each immobil- ization method has it is own advantages and disadvantages since immobilization is generally ac- companied by changes in enzymatic activity, optimum pH, temperature and stability. Depending on the type of support and immobilization process, these changes vary to a large extent (Arasaratman and Balasubramin, 1993). In this study, hydrogels of P(AAm/MA) were pre- pared at varying compositions by g-irradiation of their aqueous solutions. Hydrogels prepared from polyacryl- amide (PAAm) comprise the commonly used and investigated system in the separation purposes Radiation Physics and Chemistry 55 (1999) 713±716 0969-806X/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S0969-806X(99)00217-0 www.elsevier.com/locate/radphyschem * Corresponding author. Fax: +90 312 2977989. E-mail address: msen@eti.cc.hun.edu.tr (M. S ° en)