SLOW ELECTROGENIC EVENTS IN THE CYTOCHROME-BC1-COMPLEX OF RHODOBACTER-SPHAEROIDES - THE ELECTRON-TRANSFER BETWEEN CYTOCHROME-B HEMES CAN BE NON-ELECTROGENICстатья
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Аннотация:The flash-induced formation of transmembrane electric potential differences (measured by carotenoid bandshift) and redox changes of cytochrome b(h) (b561) 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 less-than-or-equal-to pH less-than-or-equal-to 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 b1 and b(h) hemes in the bc1 complex is, under certain conditions, accompanied by proton transfer in the same direction.