Cytosolic Isocitrate Dehydrogenase (EC 1.1.1.42) is widely distributed in animals, plants, microorganisms, and cultured cells. It catalyzes the oxidative decarboxylation of isocitrate to produce α-ketoglutarate while simultaneously reducing NADP⁺ to NADPH. ICDHc serves as another important source of NADPH in the cytoplasm, in addition to the pentose phosphate pathway, and its activity typically undergoes significant changes under stress conditions.
Assay Principle: The activity is determined by measuring the increase in NADPH concentration at 340 nm, which results from the ICDHc-catalyzed reduction of NADP⁺.