Ž . Synthetic Metals 104 1999 45–50 Immobilization of invertase in conducting polypyrrolerpolytetrahydrofuran graft polymer matrices a a a, ) ¨ b c N. Kizilyar , U. Akbulut , L. Toppare , M.Y. Ozden , Y. Yagci ˘ a Department of Chemistry, Middle East Technical UniÕersity, 06531, Ankara, Turkey b Department of Science Education, Middle East Technical UniÕersity, 06531, Ankara, Turkey c Department of Chemistry, Istanbul Technical UniÕersity, 80626, Istanbul, Turkey Received 31 July 1998; received in revised form 7 January 1999; accepted 15 January 1999 Abstract Four different polypyrrolerpolytetrahydrofuranrinvertase electrodes were constructed by the entrapment of invertase in conducting polymer matrices via electropolymerization. Immobilization of the enzyme was achieved by the application of a 1.1 V constant potential to a platinum electrode for 30 min in a solution containing 0.01 M pyrrole, 0.4 mgrml invertase and 0.4 mgrml sodium dodecyl sulphate. Performance of each electrode was optimized by examining the effects of pH and temperature on the properties of the electrodes. The changes in the maximum velocity of the reaction and variation of Michaelis–Menten constant upon immobilization were investigated. The enzyme immobilized in those matrices retained its activity for several months. q 1999 Elsevier Science S.A. All rights reserved. Keywords: Immobilization; Polypyrrole; Polytetrahydrofuran; Invertase; Electropolymerization 1. Introduction Invertase catalyses the hydrolytic breakdown of sucrose to glucose and fructose. The resulting mixture crystallizes out less readily than the household sugar and its use in confectionery thus ensures that products remain fresh and soft even when kept for longer periods of time. Soluble invertase is employed in the sweet industry in the produc- tion of noncrystallizing creams and for softening marzipan. It is also used in the production of artificial honey. Immobilization of enzymes into an inert matrix enables easy recovery and repeated use, so it is a solution to the problem of using soluble enzymes for once. Additional advantages include easy analyte determination in complex mixtures and the use of small sample volumes. Immobi- wx wx lization of invertase on corn grits 1 , gelatin 2 , carbo- wx wx hydrate moieties 3 , and polyelectrolytes 4 has been achieved. Recently, incorporation of the enzyme into conducting polymer matrices or by electropolymerization were re- ) Corresponding author. Tel.: q90-312-210-10-00; Fax: q90-312- 210-12-80; e-mail: toppare@rorqual.cc.metu.edu.tr w x ported 5–8 . Electropolymerization has merits that new properties can be easily obtained by the use of various supporting electrolytes or monomers, and the film thick- ness also can be easily controlled by regulating the amount of charge passed. Furthermore, enzyme molecules are en- trapped during electropolymerization in one step, and also that the polymer film covers the surface of the substrate w x electrode with any shape and any size 9–13 . In addition electropolymerization is simple, speedy, reliable and inex- pensive. In this study, we examined the immobilization of inver- tase in four different polypyrrolerpolytetrahydrofuran Ž . PPyrPTHF matrices, coded as PPyrMT1, PPyrMT2, PPyrTA1, and PPyrTA2. The preparation of the copoly- w x mers was described in earlier studies 14,15 . MT stands for one end pyrrole capped PTHF, and TA stands for PTHF capped with pyrrole at two ends. MT2 has longer THF segments compared to MT1, TA1 has longer THF w x segments compared to TA2 14,15 . For enzyme electrodes optimum parameters such as pH, temperature, electrolysis time, sucrose concentration; ki- netic parameters and shelf life were examined by spectro- scopic studies. 0379-6779r99r$ - see front matter q 1999 Elsevier Science S.A. All rights reserved. Ž . PII: S0379-6779 99 00033-8