An Ubiquinone-Binding Protein, A Constituent of Iron-Sulfur Fragment Isolated from Mitochondrial NADH-Ubiquinone Reductase (Complex I)
An ubiquinone-binding protein (QP) was purified from mitochondrial NADH-ubiquinone reductase (Complex I). Complex I was separated into 3 fragments: a fraction of hydrophobic proteins, that of soluble ironsulfur protein (IP) and soluble NADH dehydrogenase of flavoprotein by a procedure involving the resolution with DOC and cholate, followed by ethanol and ammonium acetate fractionations. 41% of the total ubiquinone was recovered in the IP fragment which consisted of 12 polypeptides. The QP was purified from the IP fragment with a hydrophobic affinity chromatography. SDS-polyacrylamide gel electrophoresis and immunoblotting showed that the purified QP corresponded to 14-kDa polypeptide of the IP fragment and was a different protein from the QP (12.4kDa) in Complex III. The purified QP (14 kDa) contained one mol ubiquinone per mol. The ubiquinone-depleted IP fragment could rebind ubiquinone. These results indicate that an ubiquinone-binding site in Complex I is on the 14-kDa polypeptide of the IP fragment.
KeywordsSodium Dodecyl Sulfate Ammonium Acetate Quinol Oxidase Beef Heart Mitochondrion Millimolar Extinction Coefficient
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