Lipase was partially purified from the culture supernatant of Mucor racemosus NRRL 3631. In an attempt to increase the enzyme stability, the enzyme was immobilized on poly (vinyl alcohol) PVA, radiation cross liked poly (vinyl alcohol/ vinyl pyrrolidone) PVA / PVP and poly (vinyl alcohol/ hydroxyethylmethacrylate) PVA/ HEMA hydrogels. The maximum immobilization yield (31.74 %) was obtained using PVA/ HEMA copolymer. The effect of the immobilization parameters on the enzyme such as the hydrogel

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... omposition, irradiation dose and the immobilization technique was performed. An optimum radiation dose of 15 kGy and hydrogel composition of 10 % PVA/ HEMA (9.6: 0.4 v/v) increased the immobilization yield to 60.3 %. Diffusion phenomena can be markedly increased the enzyme immobilization on the surface of the hydrogel. In this case the retained activity was approximately 81.5 % of that of the free enzyme. The profiles of immobilized enzyme activities at various pH values (4-9) and temperatures (30-80 °C) showed an overall higher stability for the immobilized enzyme than that for the free one. The half life values of the immobilized and free enzymes at 60 °C were 3.3 h and 1.73 h, respectively. The immobilized enzyme retained 69.2 % of its initial activity after three cycles.