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

Abstract

Two forms of NADP-specific isocitrate dehydrogenase ( threo-D S-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 Mn 2+ 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 it 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.