The isomer of isocitrate involved is (1R,2S)-1-hydroxypropane- -1,2,3-tricarboxylate, formerly termed threo-Ds-isocitrate.

Does not decarboxylate added oxalosuccinate.

Isocitrate dehydrogenase (IDH) is an important enzyme of carbohydrate metabolism which catalyzes the oxidative decarboxylation of isocitrate into a-ketoglutarate. IDH is either dependent on NAD+ (EC 1.1.1.41) or on NADP+(EC 1.1.1.42).

In eukaryotes there are at least three isozymes of IDH: two are located in the mitochondrial matrix (one NAD+-dependent, the other NADP+- dependent), while the third one (also NADP+-dependent) is cytoplasmic. In Escherichia coli the activity of a NADP+-dependent form of the enzyme is controlled by the phosphorylation of a serine residue; the phosphorylated form of IDH is completely inactivated.

The best conserved region of these enzymes is a glycine-rich stretch of residues located in the C-terminal section (and it's been used as a signature pattern). Two wnzymes are structurally related to IDH: 3-isopropylmalate dehydrogenase (EC 1.1.1.85) - that catalyzes the third step in the biosynthesis of leucine in bacteria and fungi; and Tartrate dehydrogenase (EC 1.1.1.93), that catalyzes the reduction of tartrate to oxaloglycolate.
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