Functional Characterization and Partial Purification of the Ubiquinol-Cytochrome c Oxidoreductase from Higher Plant Mitochondria (Helianthus tuberosus)

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Abstract
The functional and thermodynamic characteristics of the ubiquinol-cytochrome (Cyt) c oxidoreductase in a Cyt b/c1-enriched fraction (defined S-1) isolated from Jerusalem artichoke mitochondria (JAM) (H. tuberosus), were analyzed. Fraction S-1, obtained through deoxycholate-KCl fractionation procedure, contained 1 Cyt of c type (formally c1 with Em7.0 [midpoint redox potential] of +240 mV), 2 .beta. type Cyt with Em7.0 values of +100 and -25 mV, ferredoxin-like centers presumably linked to succinic- and NADH-dehydrogenases, and a Rieske-type iron sulfur center (gy = 1.89). The ubiquinol-dependent Cyt c reduction by fraction S-1 showed sensitivity to antimycin A, myxothiazol and n-hepthyl-1-hydroxyquinoline N-oxide with I50 of 12 nM, 30 nM and 0.1 mM, respectively. Oxidation-induced extra b type reduction, a widespread phenomenon of bacteria and mitochondrial respiratory systems, was also observed in both intact mitochondria and S-1 fraction. The data seem to blur previous experiments in which both spectral and functional differences between higher plant and mammalian mitochondria were underlined.