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|Title:||Isolation and characterization of NADP+ -linked isocitrate dehydrogenase of germinating pea seeds (Pisum sativum)|
|Authors:||Srivastava, P K|
Singh, D S
|Abstract:||NADP+- linked isocitrate dehydrogenase (E.C.184.108.40.206) has been purified to homogeneity from germinating pea seeds. The enzyme is a tetrameric protein (mol wt. about 146,000) made up of apparently identical monomers (subunit mol wt, about 36,000). Thermal in activation of purified enzyme at 45° and 50°C shows simple first order kinetics. The enzyme shows optimum activity at pH range 7.5-8. Effect of substrate [S] on enzyme activity at different pH (6.5-8) suggests that the proton behaves formally as an "uncompetitive inhibitor". A basic group of the enzyme (site) is protonated in this pH range in the presence of substrate only, with a pKa equal to 6.78. On successive dialysis against EDTA and phosphate Buffer, pH 7.8 at O°C, yields an enzymatically inactive protein showing kinetics of thermal inactivation identical to the untreated (native) enzyme. Maximum enzyme activity is observed in presence of Mn2+ and Mg2+ ions (3.75 mM). Addition of Zn2+, Cd2+, C02+ and Ca2+ ions brings about partial recovery. Other metal ions Fe2+, Cu2+ and Ni2+ are ineffective.|
|ISSN:||0975-0959 (Online); 0301-1208 (Print)|
|Appears in Collections:||IJBB Vol.38(5) [October 2001]|
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