Abstract
Chromatophores isolated from cells of Rhodobacter sphaeroides exposed to hypertonic solutions were enriched in cardiolipin (CL). Because CL levels are raised by increasing the incubation time of R. sphaeroides in hypertonic solutions, it was possible to isolate chromatophores containing different CL amounts by starting from cells incubated in hypertonic solutions for different times. The functionality and stability of the photosynthetic proteins in chromatophore membranes having different CL levels were investigated. Reaction center (RC) stabilization with respect to thermal denaturation and photoxidative damage was observed by flash photolysis and fluorescence emission experiments in CL-enriched chromatophores. To gain detailed information about the structures of endogenous CLs, this lipid family was isolated and purified by preparative TLC, and characterized by high-resolution mass spectrometry. We conclude that osmotic shock can be used as a tool to modulate CL levels in isolated chromatophores and to change the composition of the RC lipid annulus, avoiding membrane artifacts introduced by the use of detergents.
Highlights
Chromatophores isolated from cells of Rhodobacter sphaeroides exposed to hypertonic solutions were enriched in cardiolipin (CL)
We show that it is possible to isolate CL-enriched chromatophore membranes from R. sphaeroides exposed to high-salt-containing media, and we describe the effects of increased levels of CL on the Reaction center (RC) functionality and stability in native membranes, avoiding artifacts introduced by the use of detergents
In this study we have thoroughly examined the effects of hyperosmotic stress on the membrane lipid composition of R. sphaeroides wild-type strain and, in particular, on the CL content
Summary
Chromatophores isolated from cells of Rhodobacter sphaeroides exposed to hypertonic solutions were enriched in cardiolipin (CL). We show that it is possible to isolate CL-enriched chromatophore membranes from R. sphaeroides exposed to high-salt-containing media, and we describe the effects of increased levels of CL on the RC functionality and stability in native membranes, avoiding artifacts introduced by the use of detergents.
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