Gramicidin in chromatophores of Rhodobacter sphaeroides

Althoff, Gerd; Schönknecht, Gerald; Junge, Wolfgang

doi:10.1007/bf00196347

Cited by 5 publications

(1 citation statement)

References 20 publications

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“…The values determined in the present work for the size and the capacitance of the electric units are thus within the range of values characterizing a single chromatophore vesicle. Furthermore, the decay time of the membrane potential in the presence of gramicidin determined in this work is very similar to the decay time of the electrochromic absorption changes obtained by gramicidin titration of chromatophores from R. sphaeroides in solution [21]. From these good agreements it can be concluded that the surface of the support is covered by independent blisters formed by fusion of single chromatophores.…”

Section: Resultssupporting

confidence: 84%

Fusion of chromatophores from photosynthetic bacteria with a supported lipid layer: characterization of the electric units

Keller¹,

Riou²,

Laval³

et al. 2000

FEBS Letters

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Direct electrometric measurements of membrane potential changes are a valuable tool for study of vectorial transfer of electrons, protons, and ions. Commonly model membrane systems are created by fusion of lipid/protein vesicles with lipid-coated thin films. We characterized the electric units resulting from this process using chromatophores from the purple bacterium Rhodobacter sphaeroides and either a Mylar film or a planar modified gold electrode as support. Investigation of the shunting activity of the ionophore gramicidin on the flashinduced potential change demonstrates fusion of individual chromatophores to form independent`blisters', which preserve an interior aqueous compartment. Under current^clamp conditions the photovoltage follows the change of the membrane potential of the individual blisters. ß

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Section: Resultssupporting

confidence: 84%

Fusion of chromatophores from photosynthetic bacteria with a supported lipid layer: characterization of the electric units

Keller¹,

Riou²,

Laval³

et al. 2000

FEBS Letters

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The Electrochemical Relaxation at Thylakoid Membranes

Junge

Polle

Jahns

et al. 1992

Electrified Interfaces in Physics, Chemistry and Biology

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Connectivity of the intracytoplasmic membrane of Rhodobacter sphaeroides: a functional approach

2014

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The photosynthetic apparatus in the bacterium Rhodobacter sphaeroides is mostly present in intracytoplasmic membrane invaginations. It has long been debated whether these invaginations remain in topological continuity with the cytoplasmic membrane, or form isolated chromatophore vesicles. This issue is revisited here by functional approaches. The ionophore gramicidin was used as a probe of the relative size of the electro-osmotic units in isolated chromatophores, spheroplasts, or intact cells. The decay of the membrane potential was monitored from the electrochromic shift of carotenoids. The half-time of the decay induced by a single channel in intact cells was about 6 ms, thus three orders of magnitude slower than in isolated chromatophores. In spheroplasts obtained by lysis of the cell wall, the single channel decay was still slower (~23 ms) and the sensitivity toward the gramicidin concentration was enhanced 1,000-fold with respect to isolated chromatophores. These results indicate that the area of the functional membrane in cells or spheroplasts is about three orders of magnitude larger than that of isolated chromatophores. Intracytoplasmic vesicles, if present, could contribute to at most 10% of the photosynthetic apparatus in intact cells of Rba. sphaeroides. Similar conclusions were obtained from the effect of a ∆pH-induced diffusion potential in intact cells. This caused a large electrochromic response of carotenoids, of similar amplitude as the light-induced change, indicating that most of the system is sensitive to a pH change of the external medium. A single internal membrane and periplasmic space may offer significant advantages concerning renewal of the photosynthetic apparatus and reallocation of the components shared with other bioenergetic pathways.

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Gramicidin in chromatophores of Rhodobacter sphaeroides

Cited by 5 publications

References 20 publications

Fusion of chromatophores from photosynthetic bacteria with a supported lipid layer: characterization of the electric units

Fusion of chromatophores from photosynthetic bacteria with a supported lipid layer: characterization of the electric units

The Electrochemical Relaxation at Thylakoid Membranes

Connectivity of the intracytoplasmic membrane of Rhodobacter sphaeroides: a functional approach

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