Resolution of mitochondrial NADH dehydrogenase and isolation of two iron-sulfur proteins

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Abstract
The low MW [bovine heart] NADH dehydrogenase which can be solubilized from the mitochondrial NADH-ubiquinone oxidoreductase complex [EC 1.6.5.3] with chaotropic agents consists of 3 subunits in equimolar ratio. The largest subunit (subunit I) can be completely separated from the other 2 (subunits II + III) by treatment with sodium trichloroacetate and ammonium sulfate fractionation. Both the subunit I and subunit II + III fractions contain Fe and acid-labile S. From visible and EPR spectroscopy and the FE and acid-labile sulfide content, it is proposed that the subunit II + III fraction contains a binuclear cluster. The cluster structure present in subunit I is as yet unclear. On separation of the subunits of NADH dehydrogenase, the FMN is lost.