Isolation and properties of an isocitrate dehydrogenase from Anacystis nidulans

A NADP+-specific isocitrate dehydrogenase (EC 1.1.1.42) was isolated and purified over 400-fold from Anacystis nidulans. The enzyme activity responded slowly to rapid changes in ligand (NADP+, isocitrate, Mg2+-ions) or enzyme concentration as well as to rapid changes in temperature. These are properties characteristic of the hysteretic enzymes. In addition, the enzyme activity was subject to product (alpha-ketoglutarate) inhibition. ATP, ADP and CDP also inhibited the enzyme. Unlike several other cyanobacterial enzymes, the isocitrate dehydrogenase of Anacystis is not under redox control.