ABSTRACT
The mitochondrial system of oxidative phosphorylation is contained in the inner membrane in the form of four discrete enzyme complexes. They are the NADH:ubiquinone oxidoreductase (NADH:Q reductase), the ubiquinol:ferricytochrome c oxidoreductase (cytochrome reductase), the ferrocytochrome c:oxygen oxidoreductase (cytochrome oxidase), and the ATP-synthase. The two most remarkable features of the proton translocating enzymes of mitochondria are their enormous subunit complexity and the dual genetic origin of subunits. NADH:Q reductase was isolated from Neurospora crassa mitochondria by fractional extraction of the membrane protein with Triton X-100, followed by chromatography on DEAE-Sepharose and size exclusion HPLC performed in solutions containing 0.05% Triton X-100. The growth of membrane crystals was systematically attempted with the NADH:Q reductase, the cytochrome reductase, and the bc1-subcomplex. In order to divide the stain excluding density of the crystal to a single NADH:Q reductase molecule, the map was separated at the narrow regions between the large projecting domains.
