Comparison of Free and Immobilized L-asparaginase Synthesized by Gamma-Irradiated Penicillium cyclopium
Journal Title: Polish Journal of Microbiology - Year 2016, Vol 65, Issue 1
Abstract
Gamma irradiation is used on [i]Penicillium cyclopium[/i] in order to obtain mutant cells of high L-asparaginase productivity. Using gamma irradiation dose of 4 KGy, [i]P. cyclopium[/i] cells yielded L-asparaginase with extracellular enzyme activity of 210.8 ± 3 U/ml, and specific activity of 752.5 ± 1.5 U/mg protein, which are 1.75 and 1.53 times, respectively, the activity of the wild strain. The enzyme was partially purified by 40–60% acetone precipitation. L-asparaginase was immobilized onto Amberlite IR-120 by ionic binding. Both free and immobilized enzymes exhibited maximum activity at pH 8 and 40°C. The immobilization process improved the enzyme thermal stability significantly. The immobilized enzyme remained 100% active at temperatures up to 60°C, while the free asparaginase was less tolerant to high temperatures. The immobilized enzyme was more stable at pH 9.0 for 50 min, retaining 70% of its relative activity. The maximum reaction rate (V[sub]max[/sub]) and Michaelis-Menten constant (K[sub]m[/sub]) of the free form were significantly changed after immobilization. The K[sub]m[/sub] value for immobilized L-asparaginase was about 1.3 times higher than that of free enzyme. The ions K[sup]+[/sup], Ba[sup]2+[/sup] and Na[sup]+[/sup] showed stimulatory effect on enzyme activity with percentages of 110%, 109% and 106% respectively.
Authors and Affiliations
Heba El-Refai, Mona Shafei, Hanan Mostafa, Abdel-Monem El-Refai, Eman Araby, Fawkia El-Beih, Saadia Easa, Sanaa Gomaa
Keywords
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