NADP-specific isocitrate dehydrogenase from Escherichia coli. V. Multiple forms of the enzyme

Two forms of NADP-specific isocitrate dehydrogenase (threo-DS-isocitrate: NADP+ oxidoreductase (decarboxylating), EC 1.1.1.42) in Escherichia coli have been resolved by polyacrylamide gel isoelectric focusing and electrophoresis. Incubation of the enzyme with Mn2+ plus isocitrate prior to focusing resulted in the formation of an additional form of the enzyme, presumably the enzyme-manganese-isocitrate complex. Glycerol, a cryoprotectant used to stabilize the enzyme during purification and storage, also stabilized in during focusing, but was not necessary during electrophoresis. Thin-layer gel filtration did not reveal any differences in molecular weight between the different species of isocitrate dehydrogenase.