Effect of metal ions on the cytosolic nadp⁺- dependent isocitrate dehydrogenase from germinating blackgram, Vigna mungo (L.) Hepper

The cytosolic NADP⁺-dependent isocitrate dehydrogenase from germinating blackgram shows an absolute requirement of a divalent metal ion such as Mn²⁺ or Mg²⁺ for expression of its full activity. Other metal ions like Co²⁺, Zn²⁺ and Cu²⁺ could also activate the enzyme, though the degree of activation was lower than that of either Mn²⁺ or Mg²⁺ at the same concentration. In contrast, three metal ions Sn²⁺, Ba²⁺ and Ca²⁺ were found to be inhibitory. The kinetics analysis with ²⁺ shows sigmoidal response suggestive of a positive co-operativity in metal ion binding. The A_0.5 was 3.3 μM as deduced from a Hill plot with a Hill coefficient value of 2.1.