title: The reactions of the oxidase and reductases of Paracoccus denitrificans with cytochromes c.
abstract: Electron transport in the Paracoccus denitrificans respiratory chain system is considerably more rapid when it includes the membrane-bound cytochrome c552 than with either soluble Paracoccus c550 or bovine cytochrome c; a pool function for cytochrome c is not necessary. Low concentrations of Paracoccus or bovine cytochrome c stimulate the oxidase activity. This observation could explain the multiphasic Scatchard plots which are obtained. A negatively charged area on the "back side" of Paracoccus c which is not present in mitochondrial c could be a control mechanism for Paracoccus reactions. Paracoccus oxidase and reductase reactions with bovine c show the same properties as mammalian systems; and this is true of Paracoccus oxidase reactions with its own soluble cytochrome c if added polycation masks the negatively charged area. Evidence for different oxidase and reductase reaction sites on cytochrome c include: (1) stimulation of the oxidase but not reductase by a polycation; (2) differences in the inhibition of the oxidase and reductases by monoclonal antibodies to Paracoccus cytochrome c; and (3) reaction of another bacterial cytochrome c with Paracoccus reductases but not oxidase. Rapid electron transport occurs in cytochrome c-less mutants of Paracoccus, suggesting that the reactions result from collision of diffusing complexes.
authors.affiliation: Department of Biochemistry, Dartmouth Medical School, Hanover, New Hampshire 03577.
authors.forename: L
authors.initials: L
authors.lastname: Smith
authors.forename: H C
authors.initials: HC
authors.lastname: Davies
mesh_terms: D003574:Cytochrome c Group / Q000378:metabolism; D003576:Electron Transport Complex IV / Q000378:metabolism*; D009245:NADH Dehydrogenase / Q000378:metabolism*; D010231:Paracoccus denitrificans / Q000201:enzymology*
chemical_list: D003574:Cytochrome c Group; C031732:cytochrome C-550; D009245:NADH Dehydrogenase; D003576:Electron Transport Complex IV