Exogenous cytochrome c-dependent light-induced membrane potential generation in Rhodospirillum rubrum chromatophores

Abstract

Rhodospirillum rubrum chromatophores associated with a planar phospholipid macromembrane by bivalent cations in the presence of quinone, N, N, N′, N′-tetramethyl- p-phenylenediamine (TMPD) and ascorbate generate a transmembrane electrical potential difference in the light. Photoelectrical activity is also observed if chromatophores are preincubated with cytochrome c; the maximum values of responses are reached upon subsequent addition of ascorbate and menadion in the absence of bivalent cations and TMPD. The cytochrome c-dependent responses of the illuminated chromatophores are inhibited by Ca 2+ and prevented by quinones. The possibility of cytochrome c ( c 2) translocation across the chromatophore membrane and the mechanism of charge transfer across the planar phospholipid membrane are discussed.