[Role of cofactors in membrane potential generation by Rhodospirillum rubrum chromatophores incorporated in a teflon filter].

The chromatophores of the bacterium Rhodospirillum rubrum were incorporated into a Teflon filter impregnated with a decane solution of phospholipids and the light-induced electric potential difference (delta psi) between the aqueous phases separated by the filter was measured. The generation of delta psi in such a system at continuous light requires the presence of cofactors, i. e. artificial electron donors and acceptors. These cofactors provide for a steady-state flow of e by regenerating the reduced form of the photo-oxidized reaction center bacteriochlorophyll and by reoxidizing the photo-reduced quinone acceptor of the reaction center. The most efficient donors are the reduced forms of nitrogen-containing redox mediators, e. g. TMPD, DAD, PMS, DCPIP and methylene blue, while p-benzoquinones with E07' approximately greater than 150 mV are practically inactive. The oxidized forms of nitrogen-containing mediators and a wide variety of p-quinones with E07' down to -220 mV can be used as electron acceptors. Using inhibitor analysis and compounds with different E0' it is shown that the cofactors donate electrons immediately to the reaction center bacteriochlorophyll and accept them from a low potential deprotonated form of the primary acceptor QI, substituting the secondary acceptor QII. The inability of hydrophilic sulfonate-substituted quinones to act as acceptors suggests that QI cannot be localized on the outer surface of the chromatophores.