Mammalian dihydroorotate – ubiquinone reductase complex. II. Correlation with cytochrome oxidase, mode of linkage with the cytochrome chain, and general properties

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Abstract
Evidence is presented showing that a dihydroorotate-oxidizing system sediments with mitochondrial enzymes of beef liver in a sucrose gradient. Spectrophotometric experiments now indicate that dihydroorotate is as effective as succinate in reducing the cytochrome b content of whole and sonically disrupted mitochondria. The pyrimidine precursor also reduces the entire cytochrome chain under anaerobic conditions. Additional characterization of the dihydroorotate – ubiquinone reductase complex was carried out with regard to pH and temperature stability, and optima, metal inhibition, and behavior in gel filtration chromatography.