Isolation of a physiologically active and a physiologically inactive mitochondrial NADH-ubiquinone reductase (complex...

The method described for the isolation of mitochondrial complex I (NADH-ubiquinone reductase) from bovine hearts could not be applied to donkey hearts as unacceptably large losses in enzyme activity occurred. This method was modified for the isolation of complex I using donkey hearts and two complexes were obtained: complex IA which was physiologically inactive and complex IB which was physiologically active as it catalyzed the reaction from NADH to ubiquinone. Both complexes had relatively low enzyme activity with artificial electron acceptors, except with potassium ferricyanide, and had more or less the same amount of acid-labile sulfur and nonheme iron although the polypeptide composition differed to a great extent.