Purification and subunit structure of nicotinamide adenine dinucleotide specific isocitrate dehydrogenase from Neurospora crassa.

Neurospora crassa nicotinamide adenine dinucleotide specific isocitrate dehydrogenase (EC 1.1.1.41) has been purified to homogeneity by the criteria of disc gel electrophoresis and sedimentation equilibrium. Purification of the enzyme is facilitated by the presence of phenylmethanesulfonyl fluoride and by the use of a ribose-linked adenosine 5'-monophosphate affinity column. The enzyme appears to be composed of nonidentical subunits of molecular weights 42 800 and 38 300 as estimated by polyacrylamide gel electrophoresis in 0.1% sodium dodecyl sulfate. From the intensity of each band and the native molecular weight, it is concluded that the enzyme is composed of either six or eight subunits, three or four of each type, respectively. The availability of pure enzyme will allow clarification of the structure of the enzyme by ligand binding studies.