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Slow electrogenic events in the cytochromebc1-complex ofRhodobacter sphaeroidesThe electron transfer between cytochromebhemes can be non-electrogenic

Authors
Journal
FEBS Letters
0014-5793
Publisher
Wiley Blackwell (John Wiley & Sons)
Publication Date
Volume
284
Issue
2
Identifiers
DOI: 10.1016/0014-5793(91)80691-u
Keywords
  • Cytochromebc1Complex
  • Ubiquinone
  • Electrogenesis
  • Electron Transfer
  • Rhodobacter Sphaeroides

Abstract

Abstract The flash-induced formation of transmembrane electric potential differences (measured by carotenoid bandshift) and redox changes of cytochrome b h ( b 561) were monitored spectrophotometrically in Rb. sphaeroides chromatophores in a pH range from 7.5 to 10.0. It is shown that in the presence of antimycin A and at pH < 8.3 the myxothiazol-sensitive, antimycin-insensitive component of the carotenoid bandshift is kinetically coupled to cytochrome b h reduction. The kinetics of both processes can be described by a single exponent with a rise time of about 10 ms. Alkalization of the medium (8.3 ≤ pH ≤ 9.2) causes the appearance of an additional constituent in this phase of the carotenoid response with the rise time varying in the range of 100–300 ms. With a further pH increase (pH > 9.2), the electrogenic constituent, kinetically linked to cytochrome b h reduction, diminishes. The obtained data are discussed within the framework of the scheme, assuming that the electron transfer between b l and b h hemes in the bc 1 complex is, under certain conditions, accompanied by proton transfer in the same direction.

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