This work describes the immobilization of pullulanase onto two different polymers; agarose activated with epichlorohydrin and trichlorotriazine and casein activated with epichlorohydrin, in addition to a synthetic copolymer, butylacrylate±acrylic acid (BuA/AAc). Immobilization by covalent binding yields stable enzyme activity. The operational stability of the free and immobilized enzymes showed that the enzyme immobilized by a crosslinking technique using glutaric dialdehyde (GA) showed poor durability and the relative activity decreased sharply due to leakage after repeated washing, while the enzymes immobilized by covalent bonds resulted in a slight decrease in most cases in the relative activity (around 20%) after being used 10 times. Storage for 4±6 months showed that the free enzyme lost most of its activity, while the immobilized enzyme showed the opposite behavior. Subjecting the immobilized enzymes to doses of g-radiation (0.5±10 Mrad) resulted in complete loss in the activity of the free enzyme at a dose of 5 Mrad, while the immobilized enzymes showed relatively high resistance to g-radiation up to a dose of 5 Mrad. Nuclear Magnetic Resonance ( 1 H NMR) and FTIR measurements were carried out to con®rm the structure of the polymer as well as the immobilization process of the enzyme onto the polymeric carrier. The unique biochemical characteristics, mode of action and utility of the environmentally compatible pullulanase in starch conversion are well known. Using pullulanase with b-amylase in starch sacchari®cation processes can increase maltose yield by 20±25%.

In the present study adenosine deaminase (ADA) was immobilized onto two different polymeric materials, agarose and casein. The factors affecting the amount of enzyme attachment onto the polymeric supports such as incubation time were investigated. The maximum amount of enzyme immobilized onto different polymeric supports occurred at incubation pH value 7.5 and ADA concentration 42 units/g and the incubation time needed for the maximum amount of enzyme attachment to the polymeric supports was found to be 8 h. Some phsicochemical properties of the free and immobilized ADA such as operational stability, optimum temperature and thermal stability, pH optimum and stability, storage stability, and the effect of gamma-radiation were studied. The operational stability of the free and immobilized enzyme showed that the enzyme immobilized by a cross-linking technique using gultaric dialdehyde showed poor durability and the relative activity decreased sharply due to the leakage after repeated washing, while the enzymes immobilized by covalent bonds to the carriers showed a slight decrease in most cases in the relative activity (around 20%) after being used 10 times. Storage for 4-6 months, showed that the free enzyme lost its activity, while the immobilized enzyme showed the opposite behavior. Subjecting the immobilized enzyme to a dose of gamma radiation of 0.5-10 Mrad showed complete loss in the activity of the free enzyme at a dose of 5 Mrad, while the immobilized enzymes showed relatively high resistance to gamma radiation up to a dose of 5 Mrad.

Barley β-amlyase was immobilized on two polymeric materials; poly(acrylamide-acrylic acid) resin [P(AM-AAc)] and poly(acrylamide-acrylic acid-diallylamine-HCl) resin [P(P(AM-AAc-DAAHCl) using two different methods: covalent and cross-linking immobilization. Thionyl chloride, used to activate the polymers for covalent immobilization, has the advantage that it is able to react with a number of surface groups of protein under very mild conditions. Cross-linking with glutaraldehyde gave a higher coupling yield (approximately 70%) than covalent immobilization (approximately 20%). The activity and stability of the resulting biopolymers have been compared with those of free β-amylase. The specific activity of the immobilized enzyme was significantly influenced by the amount of enzyme loaded onto the polymers, the optimal level being 3.5 mg g −1 polymer. It was found that the immobilized β-amylase stored at 4• C retained approximately 90% of its original activity after 30 days, whereas free β-amylase stored in solution at 4• C retained only 47% of its activity after same period. The difference in long term stability was more significant when the enzyme was stored at room temperature; the immobilized enzyme maintained 40% of its activity after 30 days, whereas the residual activity of free enzyme was only 10%.

No abstract

Glucose oxidase (EC 1.1.3.4) was immobilized on different polymeric materials using different immobilization techniques (entrapping by γ -irradiation, and covalent binding using epichlorohydrin). Studies were carried out to increase the thermal stability of glucose oxidase (GOD) for different applications. The activity and stability of the resulting biopolymers have been compared with those of free GOD. The effect of different polyvinyl alcohol/polyacrylamide (PVA/PAAm) compositions of the copolymer carrier on the enzymatic activity of the immobilized GOD was studied. The maximum enzymatic activity was obtained with the composition ratio of PVA/PAAm of 60:40. The behaviour of the free and immobilized enzyme was analysed as a function of pH. A broadening in the pH profile (5.5-8) was observed for immobilized preparations. The activity and stability of the resulting biopolymers produced by immobilization of GOD onto different carriers have been compared, in both aqueous and organic media, with those of the free GOD. The enzyme's tolerance toward both heat and organic solvent was enhanced by immobilization onto polymers. The addition of different concentrations of organic solvents (10-50%, v/v) to the enzyme at higher temperature (60 • C) was found to stabilize the enzyme molecule. The strongest stabilizing effect on the enzymatic activity was achieved at a concentration of 10%.