Thermostability conditions and catalytic characterization of isocitrate dehydrogenase from Bacillus licheniformis
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The NADP+ - dependent isocitrate dehydrogenase (IDH) from Bacillus licheniformis was partially purified using ammonium sulphate fractionation and gel filtration on Sephadex G-200 column. The enzyme preparation had specific activity of 1.52 U mg-1. The temperature optimum for the IDH activity was about 59C. The Arrthenius activation energy was determined to be 65.3 kJ/mol below 47C, and 18.3 kJ/mol above this temperature. The IDH activity at 65C was much protected by isocitrate and magnesium, but no NADP+. Manganese ions were more efficient activators of the enzyme than Mg2+. Calcium ions rather inhibited the IDH. The Km values for DL-isocitrate and NADP+ in phosphate buffer (pH 7.4) at 20C were 85.5 and 4.9 muM, respectively; at 58C the corresponding values were 181.5 and 69.3 muM.
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P. Zabielski, Instytut Biologii, Uniwersytet w Bialymstoku, ul. Swierkowa 20B, 15-950 Bialystok, Poland